Predation by Gambusia holbrooki - The Plague Minnow
Predation by Gambusia holbrooki - The Plague Minnow
Predation by Gambusia holbrooki - The Plague Minnow
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Approved NSW Threat Abatement Plan<br />
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
- <strong>The</strong> <strong>Plague</strong> <strong>Minnow</strong><br />
August 2003<br />
N S W<br />
NATIONAL<br />
PARKS AND<br />
WILDLIFE<br />
SERVICE
© NSW National Parks and Wildlife Service, 2003.<br />
This work is copyright. However, material presented in this plan may be copied for personal<br />
use or published for educational purposes, providing that any extracts are fully acknowledged.<br />
Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced<br />
without prior written permission from NPWS.<br />
NSW National Parks and Wildlife Service<br />
43 Bridge Street<br />
(PO Box 1967)<br />
Hurstville NSW 2220<br />
Tel: (02) 95856444<br />
www.nationalparks.nsw.gov.au<br />
For further information contact<br />
Biodiversity Management Unit<br />
Biodiversity Research and Management Division<br />
NSW National Parks and Wildlife Service<br />
PO Box 1967<br />
Hurstville NSW 2220<br />
Tel: (02) 9585-6426<br />
Email <br />
Cover illustrations: <strong>Gambusia</strong> <strong>holbrooki</strong> – <strong>The</strong> plague minnow<br />
Illustrator: Judy Den<strong>by</strong><br />
This plan should be cited as follows:<br />
NSW National Parks and Wildlife Service (2003). NSW Threat Abatement Plan. <strong>Predation</strong> <strong>by</strong><br />
<strong>Gambusia</strong> <strong>holbrooki</strong> – <strong>The</strong> <strong>Plague</strong> <strong>Minnow</strong>. NPWS. Hurstville, NSW.<br />
ISBN 0 7313 6671 9
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Executive Summary<br />
This document constitutes the NSW National Parks and Wildlife Service (NPWS), threat<br />
abatement plan for the listed key threatening process <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> – the<br />
<strong>Plague</strong> <strong>Minnow</strong>, and as such considers the known impacts and management actions necessary<br />
to abate this threat on native fauna, in particular threatened frogs.<br />
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong>, hereafter referred to as gambusia, was listed in January<br />
1999 as a key threatening process on Schedule 3 of the NSW Threatened Species<br />
Conservation Act 1995 (TSC Act). <strong>The</strong> NSW Scientific Committee determined that predation<br />
<strong>by</strong> gambusia is a serious threat to the survival of threatened species such as the green and<br />
golden bell frog (Litoria aurea) and New England bell frog (Litoria castanea) and could<br />
cause other native frog species to become threatened. <strong>The</strong> NPWS is required to prepare a<br />
Threat Abatement Plan (TAP) to manage this key threatening process, so as to abate,<br />
ameliorate or eliminate the adverse impacts of gambusia predation.<br />
Since their introduction into Australia in 1925 for the purpose of mosquito control, gambusia<br />
have become widespread in NSW, especially modified waterways, and are considered to be a<br />
contributing factor to the decline of frogs (threatened or otherwise) as well as other native<br />
species such as freshwater fishes and macro-invertebrates.<br />
This threat abatement plan provides a strategy for the management of gambusia in NSW.<br />
Given the widespread distribution of gambusia and the difficulties posed <strong>by</strong> removing the<br />
species from the environment, this plan identifies those frog species considered most at risk<br />
from predation <strong>by</strong> gambusia in order to make the most effective use of management<br />
resources.<br />
<strong>The</strong> plan seeks to minimise ongoing human dispersal of gambusia through a program of<br />
education and awareness of the risks associated with introducing the species into the<br />
environment, particularly habitats of key threatened frog species.<br />
In addition, the plan seeks to reduce the impacts of gambusia at sites where control is most<br />
critical. <strong>The</strong> plan proposes to achieve this <strong>by</strong> undertaking a program of gambusia control at<br />
key habitats for high priority threatened frog species. At sites where gambusia removal is not<br />
considered feasible, opportunities for the creation of gambusia-free supplementary habitat<br />
will be evaluated. Sites will be monitored on an ongoing basis to assess the effectiveness of<br />
the gambusia control program.<br />
A number of research actions are recommended in order to clarify aspects of the ecology of<br />
gambusia and its impacts on frog species. Additional information is also required on the<br />
efficacy of proposed control methods and their impact on non-target species. Outcomes from<br />
this research will assist in the future management of gambusia.<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Although this threat abatement plan targets the impact of gambusia on threatened frogs. It<br />
also documents the potential effects of this on non-threatened frog species, freshwater fishes<br />
and other aquatic organisms such as macro-invertebrates. <strong>The</strong> plan recognises that effective<br />
long-term control of gambusia across the landscape will only be achieved in partnership with<br />
programs that endeavour to restore aquatic ecosystems. This plan therefore links with other<br />
broad-scale water reform processes that seek to address aspects of habitat modification<br />
favoured <strong>by</strong> gambusia.<br />
<strong>The</strong> NPWS will coordinate the implementation of this plan over a five-year period.<br />
Brian Gilligan Bob Debus<br />
Director-General Minister for the Environment<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Acknowledgements<br />
This threat abatement plan has been prepared <strong>by</strong> Ron Haering (NPWS). Background material<br />
(sections 1 to 8 of this plan) has been sourced from a review of the literature prepared <strong>by</strong> the<br />
Arthur Rylah Institute for Environmental Research under contract to the NPWS (McKay et al.<br />
2001).<br />
Ross Wellington, Nick Sheppard, (both NPWS) John Pursey, David Pollard and Jamie Knight<br />
(NSW Fisheries), Roger Dekeyzer (Environment Protection Authority), Michael Mahony<br />
(University of Newcastle) and Tony Miskiewiez (Wollongong City Council) assisted with the<br />
preparation of this plan. Thanks to Angela Arthington (Griffith University), Jack Baker,<br />
Andrew Leys, Rodney James, Melanie Bannerman, Paul Downey, Paul Mahon, and Joanne<br />
Edney (all NPWS) and Marion Anstis for their comment and/or editorial input.<br />
Special thanks are due to Michael Mahony and Marion Anstis whose expertise enabled the<br />
preparation of Appendix 3.<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
TABLE OF CONTENTS<br />
1. INTRODUCTION .........................................................................................................................1<br />
2. LEGISLATIVE FRAMEWORK .................................................................................................1<br />
2.1 COMMONWEALTH LEGISLATION ..................................................................................................1<br />
2.2 NSW LEGISLATION......................................................................................................................2<br />
3. INDUSTRY FRAMEWORK........................................................................................................6<br />
4. DESCRIPTION..............................................................................................................................6<br />
4.1 TAXONOMY AND MORPHOLOGY ..................................................................................................6<br />
4.2 DISTINGUISHING CHARACTERISTICS ............................................................................................7<br />
5. HISTORY OF INTRODUCTION................................................................................................9<br />
5.1 SPECIES ORIGIN AND ENTRY INTO AUSTRALIA ............................................................................9<br />
5.2 MOSQUITO CONTROL – SUCCESS OR FAILURE? ..........................................................................9<br />
5.3 DISPERSAL OF GAMBUSIA ...........................................................................................................10<br />
6. BIOLOGY AND ECOLOGY OF GAMBUSIA.........................................................................11<br />
6.1 DISTRIBUTION ............................................................................................................................11<br />
6.1.1 Factors influencing distribution .......................................................................................12<br />
6.2 HABITAT PREFERENCES .............................................................................................................13<br />
6.2.1 Use of modified habitats <strong>by</strong> <strong>Gambusia</strong> .............................................................................14<br />
6.3 BREEDING BIOLOGY, SOCIAL ORGANISATION AND DISPERSAL IN NATURE ...............................15<br />
Social organisation including behavioural characteristics ...........................................................16<br />
6.4 DIET AND FACTORS INFLUENCING DIETARY PREFERENCES .......................................................16<br />
6.5 KNOWN AND POTENTIAL DISEASES, PREDATORS AND COMPETITORS........................................16<br />
7. IMPACTS OF GAMBUSIA ON NATIVE PLANTS AND ANIMALS ...................................17<br />
7.1 IMPACTS ON NATIVE VEGETATION AND RIVER HEALTH............................................................17<br />
7.2 IMPACTS ON MACRO-INVERTEBRATES .......................................................................................18<br />
7.3 IMPACTS ON NATIVE FISH ..........................................................................................................18<br />
7.4 IMPACTS ON NATIVE FROGS.......................................................................................................21<br />
7.5 BENEFITS TO NATIVE PLANTS AND ANIMALS.............................................................................27<br />
8. CONTROL OF GAMBUSIA......................................................................................................27<br />
9. PROPOSED MANAGEMENT OF GAMBUSIA ......................................................................29<br />
9.1 INTRODUCTION...........................................................................................................................29<br />
9.2 THREAT ABATEMENT ACTIONS..................................................................................................29<br />
10. ECONOMIC AND SOCIAL IMPACTS OF THE PLAN ...................................................36<br />
11. REVIEW DATE ......................................................................................................................36<br />
12. REFERENCES AND PERSONAL COMMUNICATIONS ................................................37<br />
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APPENDIX 1: NSW SCIENTIFIC COMMITTEE FINAL DETERMINATION .........................50<br />
APPENDIX 2: NSW RIVERS SURVEY RECORDS OF GAMBUSIA...........................................51<br />
APPENDIX 3: DEVELOPMENT OF A RANK SCORING SYSTEM TO PREDICT<br />
GAMBUSIA IMPACT ON NATIVE FROG SPECIES....................................................................53<br />
APPENDIX 4: THREAT ABATEMENT PLAN COST TABLE.....................................................62<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Introduction<br />
<strong>Gambusia</strong> has been colloquially described as the ‘animal weed’ of our aquatic environment, because of its<br />
ability to rapidly reproduce, disperse widely and occupy diverse habitats, to the detriment of native<br />
species. This small, introduced fish is also highly aggressive and predatory.<br />
Originally introduced in 1925 from the USA into the Royal Botanic Gardens Sydney, for the purpose of<br />
mosquito control. <strong>Gambusia</strong> are now common and widespread, occurring in most freshwater habitats in<br />
south-eastern Australia, as well as the coastal drainages of Queensland, and some parts of the Northern<br />
Territory and Western Australia. It has been an extremely successful invader assisted <strong>by</strong> human dispersal<br />
and facilitated <strong>by</strong> its high reproductive potential, fast maturation rate, flexible behaviour and broad<br />
environmental tolerances. In five months, a population of gambusia can increase to over 100,000 fish<br />
after natural mortalities.<br />
<strong>The</strong> effectiveness of gambusia to control mosquitoes has generally failed internationally and the World<br />
Health Organisation no longer recommends its use for malaria control programs primarily due to its<br />
harmful impact on native fish. What remains however, is the legacy of another introduced species<br />
establishing itself in Australia and impacting on native species including frogs, fish and macroinvertebrates.<br />
<strong>Predation</strong> <strong>by</strong> gambusia is now listed as a key threatening process in NSW.<br />
<strong>The</strong>re are presently no effective and specific methods to control gambusia. Once introduced, it is almost<br />
impossible to eradicate from the environment, particularly from connected waterways such as creeks,<br />
rivers and streams, and large permanent water bodies. A number of physical, chemical and biological<br />
approaches have been trialled with varying degrees of success and inherent risks. An integrated targeted<br />
strategy is proposed in this plan, which combines public education, gambusia control (where feasible) and<br />
ecological rehabilitation. Actions identified in the plan are targeted predominantly towards ameliorating<br />
the impacts of gambusia on frogs, particularly threatened frog species.<br />
1. Legislative Framework<br />
2.1 Commonwealth Legislation<br />
Wildlife Protection (Regulation of Exports and Imports) Act 1982<br />
Regulations concerning the import of exotic species and export of native species are provided under the<br />
Wildlife Protection (Regulation of Exports and Imports) Act 1982. Schedule 6 of the Act includes a list of<br />
fish, which can be imported into Australia. <strong>Gambusia</strong> are not included on this list. Persons wishing to<br />
import gambusia would need to have the species approved for inclusion on this Schedule.<br />
Given the widespread availability of the species in Australian waterways and its lack of value as an<br />
ornamental fish (see section 3), it is unlikely that gambusia would knowingly be imported into Australia.<br />
Environment Protection and Biodiversity Conservation Act 1999<br />
<strong>The</strong> impacts of gambusia are not listed as a key threatening process under this Act.<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
2.2 NSW Legislation<br />
Threatened Species Conservation Act 1995<br />
<strong>The</strong> NSW Threatened Species Conservation Act 1995 (TSC Act) aims to conserve biological diversity,<br />
prevent extinction and promote the recovery of listed species, populations and ecological communities.<br />
<strong>The</strong> ultimate goal of the TSC Act is to recover threatened species, populations and ecological<br />
communities, so that their long-term survival in nature can be assured. This involves eliminating or<br />
managing processes that threaten the survival or evolutionary development of such species. <strong>The</strong> key<br />
mechanisms provided in the TSC Act to achieve this goal are the preparation and implementation of<br />
recovery plans and threat abatement plans.<br />
<strong>The</strong> TSC Act provides for the listing of key threatening processes. A threatening process is eligible to be<br />
listed if, in the opinion of the Scientific Committee it:<br />
a) adversely affects two or more threatened species, populations or ecological communities, or<br />
b) could cause species, populations or ecological communities that are not threatened to become<br />
threatened<br />
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> the <strong>Plague</strong> <strong>Minnow</strong> was gazetted as a key threatening process under the<br />
TSC Act in January 1999. <strong>The</strong> final determination of the NSW Scientific Committee is provided in<br />
Appendix 1. <strong>The</strong> rationale for this determination is based on the view that predation <strong>by</strong> gambusia is a<br />
serious threat to the survival of threatened species such as the green and golden bell frog (L. aurea) and<br />
New England bell frog (L. castanea) and other native frog species. <strong>The</strong> NPWS is therefore required to<br />
prepare a TAP to manage this key threatening process, so as to abate, ameliorate or eliminate the adverse<br />
impacts of gambusia predation on threatened species.<br />
This plan constitutes the final approved TAP for this listed key threatening process. <strong>The</strong> TSC Act requires<br />
Ministers and public authorities to take any appropriate action available to them to implement the<br />
measures included in the plan for which they are responsible. Furthermore, they must not make decisions<br />
that are inconsistent with the provisions of the plan. A public authority identified in a plan as responsible<br />
for the implementation of particular measures must report to Parliament on actions taken to implement<br />
those measures. <strong>The</strong> NPWS has been identified as the implementation authority for this TAP.<br />
<strong>The</strong> TSC Act requires the final approved recovery plan to include a summary of advice given in the NSW<br />
Scientific Committee submission to the draft plan and a reason for any departure from that advice. In<br />
regard to this plan, the NSW Scientific Committee commented that overall, the plan is logical and well<br />
focused. <strong>The</strong> Scientific Committee also noted that the frog ranking system provided in Appendix 3,<br />
should be periodically updated as ongoing research clarifies the uncertainty about which native frog<br />
species are most at risk from predation <strong>by</strong> gambusia.<br />
Fisheries Management Act 1994<br />
<strong>The</strong> Fisheries Management Act 1994 (FM Act) aims to conserve, develop and share the fishery resources<br />
of NSW for the benefit of present and future generations. <strong>The</strong> objectives of this Act relate to conserving<br />
fish stocks and protecting key habitats, conserving threatened species, populations and communities,<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
promoting ecologically sustainable development, promoting viable commercial fishing and aquaculture<br />
industries, promoting quality recreational fishing opportunities and sharing fisheries resources between<br />
users.<br />
NSW Fisheries are responsible for the management of fish resources in NSW and has management<br />
responsibility for all aquatic animals (with the exception of aquatic mammals, birds, reptiles and<br />
amphibians which are managed <strong>by</strong> NSW NPWS) including fish and their habitat in all waters of the State<br />
(including private and public waters and all permanent and intermittent waters). Through amendments to<br />
the FM Act, NSW Fisheries are responsible for threatened fish species, populations and ecological<br />
communities and for the conservation of biodiversity of all fish and marine vegetation.<br />
Like the TSC Act, the FM Act includes provision for the listing of threatened species, populations and<br />
ecological communities and key threatening processes and includes provisions for the preparation of<br />
recovery plans and threat abatement plans. <strong>The</strong> NSW Fisheries Scientific Committee has made a final<br />
recommendation to list the “Introduction of fish to fresh waters within a river catchment outside their<br />
natural range” as a key threatening process. This listing cites the impacts of gambusia as part of this<br />
threatening process.<br />
Noxious fish and noxious marine vegetation<br />
<strong>The</strong> FM Act, Part 7, Division 6 (Sections 209 to 213) provides for the declaration of different categories<br />
of noxious fish (which represent the different levels of threat they pose to the aquatic environment) and<br />
includes penalties for their sale and possession. It is a defence against prosecution under Section 211 if a<br />
person neither introduced nor maintained a noxious fish in those waters. Conditions may be included in<br />
aquaculture permits for the destruction or control of noxious fish. Section 213 enables the destruction of<br />
noxious fish.<br />
<strong>Gambusia</strong> is not currently declared a noxious fish in NSW.<br />
Clarke et al. (2000) reviewed the status of gambusia in other Australian states. It is classified as a pest in<br />
Queensland under the Fisheries Act 1994, where the species may not be released into waters or held in<br />
captivity. In Western Australia gambusia must not be returned to the water. In Victoria, it is listed as a<br />
noxious species under the Fisheries Act 1995.<br />
Release or importation of fish<br />
Part 7, Division 7 (Section 216) of the FM Act prohibits the release of any live fish (except under a<br />
permit) into any waters. Section 217 prohibits any person bringing live fish into NSW not taken from<br />
NSW waters except under permit. A person who sells or buys or has possession of a fish knowing it has<br />
been brought into the State is guilty of an offence.<br />
This section of the FM Act applies only to the release of fish into the sea, river, creek or other naturally<br />
flowing stream or water or into a lake. This excludes other waterbodies such as farm dams, outdoor ponds<br />
or other forms of aquaria.<br />
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NSW Fisheries – Introduction and Translocation Policy<br />
This policy provides background on the introduction of native and non-native fish species, translocations,<br />
aquaculture, impact of introductions/translocations and legislation. <strong>The</strong> policy states:<br />
7.1 All stockings of fish into NSW waters require a permit from NSW Fisheries.<br />
7.2 NSW Fisheries will not permit any further introductions or translocations of native or nonnative<br />
species into NSW waters, except as permitted elsewhere in this policy.<br />
NSW Fisheries distinguishes between exotic, alien, introduced and translocated species. <strong>Gambusia</strong> are<br />
classified as alien, ie a species which was brought into Australia from a foreign country and has<br />
established wild populations. This policy notes that species such as gambusia have been introduced into<br />
the State either accidentally or deliberately.<br />
Environmental Planning and Assessment Act 1979<br />
Land use within NSW is primarily regulated <strong>by</strong> the Environmental Planning and Assessment Act 1979<br />
(EP&A Act). <strong>The</strong> EP&A Act seeks to encourage, inter alia, ecologically sustainable development <strong>by</strong><br />
managing the development process and the effects of development on the environment.<br />
When evaluating a proposed development or activity, consideration <strong>by</strong> a consent or determining authority<br />
should be given to the potential of that proposed development or activity, resulting in the introduction of<br />
gambusia into the natural environment, including its effects on threatened species (Section 79C and<br />
Section 111 of the EP&A Act).<br />
In addition, Section 5A of the EP&A Act sets out eight factors to be considered when deciding whether<br />
there is likely to be a significant effect on threatened species, populations and ecological communities and<br />
hence, if a Species Impact Statement (SIS) is required. Part (g) of this ‘eight part test’ includes the<br />
following factor for consideration - whether the development or activity proposed is of a class of<br />
development or activity that is recognised as a threatening process. This part would be relevant if, for<br />
example, a proposed development was likely to result in the introduction of gambusia into an area.<br />
It is a requirement of the NPWS that all proposed activities (including pest control) on NPWS land are<br />
assessed under Part 5 of the EP&A Act. This involves an examination of whether the activity is likely to<br />
significantly affect the environment, including threatened species, populations and ecological<br />
communities and their habitats. <strong>The</strong> mechanism to undertake this assessment is generally regarded as a<br />
Review of Environmental Factors. Where a significant effect is likely, the EP&A Act requires the<br />
preparation of an environmental impact statement, and in the case of a significant effect on threatened<br />
species, populations or ecological communities, a SIS.<br />
Pesticides Act 1999<br />
<strong>The</strong> Pesticides Act regulates and controls the use of pesticides within NSW. Under the Act, it is illegal to<br />
possess, prepare for use, or use a pesticide in NSW unless it is registered <strong>by</strong> the National Registration<br />
Authority for agricultural and veterinary chemicals (NRA) or covered <strong>by</strong> an NRA permit issued under the<br />
Commonwealth Agricultural and Veterinary Chemical Code Act 1994. <strong>The</strong> Pesticides Act requires strict<br />
adherence to label instructions, as set out <strong>by</strong> the NRA, when using a registered pesticide.<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
<strong>The</strong> Pesticides Act also makes it an offence to use a pesticide in a way that harms any non-target animal<br />
or plant. A defence against prosecution is provided where a person takes all reasonable precautions and<br />
exercises all due diligence when using the pesticide and the offence was due to causes beyond the<br />
person’s control.<br />
Rotenone for example, is a registered pesticide commonly used in various formulations such as ‘Derris<br />
Dust’ for agricultural pest control purposes. Rotenone is also an effective broad- spectrum piscicide that<br />
is toxic to most fish and has been used to kill pest fish species such as carp and gambusia (Hall 1988;<br />
Sanger and Koehn 1997; Koehn et al 2000; Willis and Ling 2000). Its application has generally been<br />
limited to small closed water bodies such as ponds or farm dams.<br />
Rotenone is not currently registered as a piscicide in Australia. <strong>The</strong> application of Rotenone to remove<br />
gambusia would therefore require its registration as a piscicide with the NRA and approval for its use<br />
from the NSW Environment Protection Authority and NSW Fisheries. Before registering any product, the<br />
NRA is required to conduct a rigorous assessment of its potential impacts on the environment, human<br />
health and trade and of its likely effectiveness for its proposed uses. Alternatively, the NRA can consider<br />
issuing either an ‘off-label’ permit for unregistered/registered products for minor or emergency uses, or a<br />
trial permit for research purposes to determine its efficacy data and assess non target impacts.<br />
Water Management Act 2000<br />
<strong>The</strong> Water Management Act 2000 (WM Act) is the principal piece of legislation controlling water<br />
management across NSW and is administered <strong>by</strong> the NSW Department of Land and Water Conservation<br />
(DLWC). <strong>The</strong> WM Act provides for the development of water sharing plans and water management plans<br />
<strong>by</strong> community based Water Management Committees (which includes NPWS representation). <strong>The</strong> WM<br />
Act may allocate the volume of water to be used for various purposes, including irrigation and<br />
environmental flows, identify the timing of water extraction for various purposes and discuss the natural<br />
flow regimes of a catchment or subcatchment.<br />
Water plans must be consistent with government advice and policy, including the Interim State Water<br />
Management Operating Plan, which sets the overarching policy context, targets and strategic outcomes<br />
for the States’s water resources.<br />
Catchment Management Amendment Bill 2001 (not yet passed) and the Catchment Management<br />
Act 1989<br />
<strong>The</strong> amendments to the Catchment Management Act 1989 (CM Act) will provide that certain plans<br />
prepared under the WM Act must be consistent with any relevant catchment management plan. <strong>The</strong><br />
Catchment Management Plans (also called "blueprints") are expected to drive regional investment<br />
priorities under the National Action Plan for Salinity and Water Quality and the Natural Heritage Trust<br />
Mark 2. <strong>The</strong> establishment of Catchment Management Boards on which NPWS is represented will drive<br />
the development of these catchment management plans.<br />
NSW Weirs Policy (1995)<br />
<strong>The</strong> NSW Weirs Policy is a component of the State Rivers and Estuaries Policy (1991) being<br />
implemented <strong>by</strong> DLWC. <strong>The</strong> goal of the State Weirs Policy is to halt and where possible reduce and<br />
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remediate the environmental impacts of weirs. <strong>The</strong> review of weirs will assist with the development of<br />
operational and structural changes needed to achieve river flow and water quality objectives.<br />
NSW Wetlands Management Policy (1996)<br />
<strong>The</strong> NSW Wetlands Management Policy adopts nine principles that aim to minimise any further loss or<br />
degradation of wetlands and, where possible, restore degraded wetlands. Principle six states that “Natural<br />
wetlands should not be destroyed, but when social or economic imperatives require it, the rehabilitation or<br />
construction of a wetland should be required”. This policy is consistent with the objectives of the WM<br />
Act. This policy is also being implemented <strong>by</strong> DLWC.<br />
3. Industry Framework<br />
<strong>Gambusia</strong> are unlikely to play an important role in the aquarium industry and due, to its ubiquitous<br />
distribution is unlikely to be imported specifically as an ornamental fish for the aquarium trade. In NSW,<br />
aquarium retail outlets are currently permitted to trade in gambusia supplied from local sources. It is<br />
principally traded as a fish to be fed to other aquarium fish, being readily available from local sources<br />
(Jared Patrick pers. comm.). <strong>The</strong> number of gambusia traded in this manner is difficult to estimate. As<br />
they are sourced locally and are relatively inexpensive, it is unlikely that any significant numbers are sold.<br />
4. Description<br />
4.1 Taxonomy and Morphology<br />
<strong>Gambusia</strong> <strong>holbrooki</strong> (Girard 1859)<br />
Order: Cyprinodontiformes<br />
Family: Poeciliidae<br />
Common name: Eastern <strong>Gambusia</strong>, Mosquito Fish, <strong>Plague</strong> <strong>Minnow</strong><br />
<strong>The</strong> history of introduction(s) and subsequent spread of gambusia are poorly documented and confusion<br />
exists regarding which subspecies is actually present in Australia (Lloyd and Tomasov 1985). <strong>The</strong>re is<br />
confusion about the correct species name in Australia (Howe 1995). <strong>The</strong> following summary of taxonomy<br />
should clarify this.<br />
<strong>The</strong>re are approximately 30 species within the genus gambusia most of which are rare and restricted in<br />
range (Rivas 1963; Rosen and Bailey 1963). Prior to studies <strong>by</strong> Lloyd and Tomasov (1985), authors<br />
named the Australian introduction as <strong>Gambusia</strong> affinis, which is originally distributed from across southeastern<br />
USA to Texas (Lloyd and Tomasov 1985). Two subspecies of G. affinis were subsequently<br />
identified in south-eastern USA: the eastern form G. affinis <strong>holbrooki</strong> (Krumholz 1948) and the western<br />
form, G. affinis affinis (Baird and Girard 1853). Lloyd and Tomasov (1985) confirmed Wilson’s (1960)<br />
interpretation that the subspecies G. a. <strong>holbrooki</strong> is the taxon introduced into Australia. Wooten et al.<br />
(1988) later reinstated the original species G. <strong>holbrooki</strong> (Girard 1859) and G. affinis (Baird and Girard<br />
1853) into two species. <strong>The</strong> species found in Australia is presently named G. <strong>holbrooki</strong> (Lloyd and<br />
Tomasov 1985; Arthington et al. 1999).<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
In about 1905, “mosquitofish” was adopted as the common name for gambusia (Lloyd 1990a), replacing<br />
the previous (American) name “topminnow” (Krumholz 1948; Lloyd 1990). <strong>The</strong> name mosquitofish<br />
implied that gambusia was as an effective mosquito control agent, making it the “logical” choice for the<br />
solution to mosquito control problems without first considering the use of native fish as potential control<br />
agents (Lloyd 1990a). <strong>Gambusia</strong> is now commonly referred to as the plague minnow, in light of its<br />
proliferation in Australian waters.<br />
<strong>The</strong> following description of the morphology of gambusia is adapted from McDowall (1996) and<br />
Cadwallader and Backhouse (1983):<br />
Body: A tiny, stout fish with a deep rounded belly and a flattened upper surface, especially the head<br />
Eyes: large, positioned near dorsal profile<br />
Mouth: small, upturned and protrusible, lower jaw a little longer than upper. Bands of minute teeth on<br />
both jaws<br />
Scales: head and body covered with large cycloid scales (28-32, usually 30-31 laterally)<br />
Dorsal fin: single, soft rayed (6-8 rays, usually 7), short based, high, rounded, and situated posteriorly<br />
Anal fin: (9-11 rays, usually 10) rounded or elongate, pointed<br />
Pectoral fins: short, rounded, positioned high on sides near top of gill openings<br />
Pelvic fins: abdominal, tiny rounded; bases close together. Caudal fin large, rounded<br />
Lateral Line: no lateral line<br />
Vertebrae: 31-33<br />
Gill rakers: 13-15 stout gill rakers of moderate length<br />
<strong>Gambusia</strong> is sexually dimorphic, with females much larger bodied than males (maximum standard<br />
lengths of 35 mm and 60 mm respectively) (McDowall 1996; Cadwallader and Backhouse 1983). Males<br />
cease growing when they reach maturity, but females continue to grow until they die (Cadwallader and<br />
Backhouse 1983; Vargas and de Sostoa 1996).<br />
<strong>Gambusia</strong> are generally green olive to brown on the back, the sides are grey with a bluish sheen, and the<br />
belly is silvery-white (Cadwallader and Backhouse 1983; McDowall 1996). <strong>The</strong> lower jaw is steel blue<br />
and often has a dark, diagonal stripe below the eye. Fins are colourless, except for the dorsal and caudal<br />
fins, which may bear numerous fine black spots, sometimes forming indistinct rows. Individuals of some<br />
populations of gambusia have brownish-black spots on the sides (Cadwallader and Backhouse 1983).<br />
Females have a distinct black blotch surrounded <strong>by</strong> a golden patch just above the vent. Males have a<br />
highly modified anal fin, the third, fourth and fifth rays of which are elongated and thickened with very<br />
small hooks at the tip. <strong>The</strong>se form the gonopodium or intromittent organ, used to facilitate internal<br />
fertilisation of eggs in the female (Cadwallader and Backhouse 1983; McDowall 1996).<br />
4.2 Distinguishing Characteristics<br />
<strong>The</strong>re are no other species of gambusia present in NSW. However, there are several native and introduced<br />
species, which may potentially be confused with gambusia (Table 1).<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Table 1. Fish species occurring in NSW, which could potentially be confused with gambusia<br />
Common name and scientific name Distinguishing features Distribution Habitat conditions<br />
Darling River Hardyhead<br />
Protrusible mouth and thin lips. Scales almost Upper tributaries of Darling Gently flowing, shallow, clear water<br />
Craterocephalus amniculus<br />
circular and barely overlapping.<br />
River<br />
or in aquatic vegetation at the edges of<br />
(Small individuals can be confused with gambusia)<br />
such waters.<br />
Murray Hardyhead<br />
Mouth restricted <strong>by</strong> a labial ligament from 1/3 too Once abundant in southern A highly mobile schooling fish that<br />
Craterocephalus fluviatilis<br />
halfway along the thin lips. Scales on top of head waters of inland NSW. No often found over very sandy shallow<br />
robust and large, with a single large interorbital records in the past 10 years flats.<br />
(Small individuals can be confused with gambusia)<br />
scale reaching as far as the anterior margin.<br />
Marjorie’s Hardyhead<br />
Craterocephalus marjoriae<br />
(Small individuals can be confused with gambusia)<br />
Flyspecked Hardyhead<br />
Craterocephalus stercusmuscarum fulvus<br />
(Small individuals can be confused with gambusia)<br />
Pacific blue-eye<br />
Pseudomugil signifer<br />
(Small individuals can be confused with gambusia)<br />
Guppy<br />
Poecilia reticulata*<br />
(Small individuals can be confused with gambusia)<br />
Swordtail<br />
Xiphophorus helleri*<br />
(Small individuals can be confused with gambusia)<br />
Platy<br />
Xiphophorus maculatus*<br />
(Small females may be confused with female gambusia)<br />
8<br />
Head usually blunt, slightly flattened and sloping<br />
towards snout. Mouth protrusible, with small,<br />
sharp, inwardly pointing teeth<br />
Small fish, more slender than most hardyheads;<br />
head in larger specimens tending to slope<br />
downwards toward snout. Lips moderately thick; a<br />
small protrusible mouth.<br />
Small fish, semi-transparent body which can vary<br />
in colour from pale olive, yellow and blueish. <strong>The</strong><br />
iris of the pacific blue eye is blue. <strong>The</strong>re is often a<br />
line of pearly spots along the side of the body.<br />
Males can grow to 88 mm, females to 63 mm in<br />
length.<br />
Single dorsal fin a little behind middle of body.<br />
Males brightly coloured with irregular markings of<br />
green, turquoise, blue, red, orange and yellow.<br />
Modest size, dorsal fin high on arching back. Tail<br />
truncated, lower margin elongated to form a long<br />
sword in male. Aquarium fish are bright orange on<br />
body and fins; wild populations olive brown with<br />
orange-red midlateral stripe.<br />
Very deep bodied and much compressed, with<br />
dorsal fin high on arching back.<br />
Clarence River in northeastern<br />
NSW<br />
Previously present in most<br />
parts of the Murray-Darling<br />
drainage system in NSW<br />
East coast of Australia, from<br />
Cooktown in Queensland to<br />
Narooma in NSW.<br />
Occurring in coastal<br />
drainages of northern NSW<br />
Occurring in coastal<br />
drainages of northern NSW<br />
Occurring in coastal<br />
drainages of northern NSW<br />
(Ivantsoff and Crowley 1996; Arthington and McKenzie 1997; Allen 1989; McDowall 1996; Australian Museum 2002). * Introduced species.<br />
Often found in large schools in<br />
shallow water with a gravelly or<br />
sandy bottom though also frequents<br />
weedy sections of streams.<br />
Usually schools in still or gently<br />
flowing water over sand, gravel or<br />
mud.<br />
Prefers clear fast flowing streams and<br />
mangrove regions of estuaries.<br />
Still or gently flowing waters. Around<br />
margins and edges of aquatic<br />
vegetation. Prefers water above 15C.<br />
Gently flowing streams with sparse<br />
vegetation over gravelly substrates.<br />
Prefers still warm water above 20C.
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
5. History of Introduction<br />
5.1 Species Origin and Entry into Australia<br />
<strong>Gambusia</strong> are native to southern USA and Northern Mexico (Lloyd and Tomasov 1985;<br />
Clarke et al. 2000). <strong>The</strong> native range of gambusia is the area from central Alabama, east into<br />
Florida and throughout the Atlantic coastal drainages northwards to New Jersey (Rivas 1963;<br />
Wooten et al. 1988).<br />
<strong>Gambusia</strong> was introduced into Australia in 1925 from Georgia (USA) (Wilson 1960; Myers<br />
1965; Bayly and Williams 1973; McKay 1984), to control mosquitoes, and was first released<br />
into the Botanical Gardens in Sydney (Bayly and Williams 1973; McKay 1984). In 1926, the<br />
Chief Health Inspector of the City of Sydney established wild populations from specimens<br />
imported from another introduced location, Italy (Wilson 1960; Clarke et al. 2000). <strong>Gambusia</strong><br />
was introduced to other parts of NSW from 1927 onwards until World War II, when it was<br />
widely established in the state. Until about 1930, city and Municipal Councils distributed fish<br />
in the Newcastle and northern coastal regions (Wilson 1960). In 1940, gambusia were flown<br />
to Darwin. During World War II they were spread through military camps in many parts of<br />
Australia (Myers 1965; Boulton and Brock 1999). <strong>Gambusia</strong> are reported to have been<br />
released into some parts of NSW for the purpose of mosquito control, eg in the Illawarra and<br />
Central Coast areas as late as the 1960s (Ross Wellington pers. comm.).<br />
5.2 Mosquito Control – Success or Failure?<br />
During the early 1900s, after it was discovered that mosquitoes transmit both malaria and the<br />
deadly yellow fever, public health officials and doctors worldwide began to show an interest<br />
in reducing or eradicating those diseases <strong>by</strong> attacking mosquito at their larval stages (Myers<br />
1965; Boulton and Brock 1999). Many attempts have been made to reduce the problems<br />
caused <strong>by</strong> mosquitoes, with many mosquito control options suggested, including physical and<br />
chemical methods. <strong>The</strong> search for a natural control method for mosquitoes led to the concept<br />
of biological control (Lloyd 1990a).<br />
<strong>Gambusia</strong> was first used in 1905 as a mosquito control agent, when specimens from Texas<br />
were released in Hawaii (Krumholz 1948; Wilson 1960). Public health authorities were<br />
delighted <strong>by</strong> the hardiness of the so-called ‘mosquitofish’ and the ease with which it spread<br />
(Boulton and Brock 1999). American research on mosquito-destroying fishes was thus<br />
concentrated mostly on the mosquitofish, which gradually became known throughout the<br />
world as THE fish to introduce in the fight against mosquito-transmitted diseases (Myers<br />
1965).<br />
Wilson (1960) emphasises the general opinion of many people at the time in Australia that<br />
gambusia was successful in controlling mosquitoes. He stated that gambusia was of distinct<br />
value as a mosquito control agent, which exerts good control of mosquitoes in permanent<br />
pond habitats. However, Wilson (1960) also considered that the use of gambusia in Newcastle<br />
and the north coast of NSW was unsuccessful.<br />
9
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Since 1982, the World Health Organisation (WHO) has no longer recommended the use of<br />
gambusia for malaria control programs and indicates that it should not be introduced into new<br />
areas, primarily because of its apparent harmful impact on native fish species (Legner 1996).<br />
Views on the effectiveness of gambusia as a mosquito control agent vary. Lake (1971), for<br />
instance, stated "I believe their effect on mosquitoes has been negligible". Grant (1978) noted<br />
that it was arguable whether gambusia offers better mosquito control than some native fish.<br />
Studies in Australia indicate that gambusia is not an effective mosquito predator, with<br />
mosquitoes only making up a small part of its diet (Lloyd 1984; Lloyd 1986). In another study<br />
in the lower River Murray, only 10% of the diet of gambusia consisted of mosquito larvae,<br />
whereas four endemic fish species consumed more mosquitoes (Lloyd 1986; Arthington and<br />
Lloyd 1989). Reddy and Pandian (1972) found heavy mortalities of gambusia reared on a diet<br />
restricted to mosquito larvae, and the few survivors showed poor growth and delayed<br />
maturation.<br />
Several authors have observed that gambusia may actually encourage mosquito populations<br />
<strong>by</strong> preying on their invertebrate predators (Stephanides 1964; Hoy et al. 1972; Hurlbert et al.<br />
1972; Hurlbert and Mulla 1981). <strong>Gambusia</strong> are inappropriate for mosquito control in certain<br />
habitats such as temporary ponds, waters with dense vegetation and running waters. It is also<br />
unlikely to be effective as a predator on cool cloudy days, where drops in temperature and<br />
oxygen occur (Lloyd 1986). Where good mosquito larvae control has been reported, the<br />
evidence was largely anecdotal or derived from poorly designed experiments (Courtenay and<br />
Meffe 1989; Rupp 1996).<br />
5.3 Dispersal of <strong>Gambusia</strong><br />
<strong>Gambusia</strong> can be spread either directly or indirectly <strong>by</strong> humans, naturally through floods, or<br />
perhaps <strong>by</strong> other animals such as birds feeding on and regurgitating small fish, dropping them<br />
in flight, or transporting fish on mud adhered to their plumage and feet. Lloyd (1987) states<br />
that humans were the major dispersal agents of gambusia. McKay (1984) also observed that<br />
past records of gambusia around Alice Springs were probably a result of the release of<br />
aquarium fish.<br />
<strong>The</strong> NPWS is not aware of any local councils or health authorities in NSW currently<br />
advocating the introduction of gambusia as a mosquito control agent. However, individuals<br />
from the public, without realising the impact that the species has on the environment, may<br />
still move these fish around, believing that gambusia are efficient at removing mosquito<br />
larvae from waterways or simply to dispose of unwanted fish. Some argue that gambusia are<br />
safe when used in the “contained” and artificial environments in which they are often stocked,<br />
and will not escape to the wild (Meffe 1996). It is also likely that some people move<br />
gambusia around believing them to be native species (Ross Wellington pers. comm.).<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Flooding of waterways is another potential mechanism for the dispersal of gambusia. One<br />
example, is the Brisbane flood of January 1974, which caused widespread flooding of<br />
suburban creeks and a number of outdoor ponds and indoor aquaria, which resulted in fish<br />
being liberated (McKay 1984). Most outdoor ponds, which are thought to be secure<br />
environments, are not fitted with an outlet screen to prevent the discharge of aquarium fish<br />
into storm water drains (McKay 1984). Down-stream ponds in particular are prone to<br />
reinfection <strong>by</strong> gambusia sourced upstream during flooding events.<br />
<strong>Gambusia</strong> has been known to spread from overcrowded pools into wheel ruts or puddles after<br />
heavy rainfall (Serventy and Raymond 1980; Wager 1995a). In one reported case a number of<br />
fish were found 275 m from the parent lake, swimming along the tiny stream formed <strong>by</strong> a<br />
wheel rut (Serventy and Raymond 1980).<br />
Lloyd (1987) observed that the distribution of gambusia in isolated waterbodies in central<br />
Australia was almost certainly a result of flooding. <strong>Gambusia</strong> are known to be present in<br />
artificial water bodies on the Nullabor Plain (Serventy and Raymond 1980; Boulton and<br />
Brock 1999). Irrigation channels could be a potential source of infestation of gambusia into<br />
near<strong>by</strong> creeks and rivers. Wager (1995a) found gambusia to be common in artificial habitats<br />
such as bore drains and the wetlands associated with some flowing bores in the Diamantina<br />
River Catchment in western Queensland. <strong>The</strong>se artificial habitats probably act as point<br />
sources for the ongoing infestation of surrounding water bodies (Wager 1995a). <strong>Gambusia</strong><br />
has been recorded in several floodplain waterholes in the Cooper Creek drainage (Angela<br />
Arthington, pers. obs.).<br />
Lloyd (1984) indicated that adults do not move beyond their home range although they can<br />
undertake small scale thermal migrations within this area, while it has been noted that<br />
juveniles tend to migrate away from adult populations (Lloyd 1986).<br />
6. Biology and Ecology of <strong>Gambusia</strong><br />
6.1 Distribution<br />
In Australia, gambusia are found in at least eight of the eleven major drainage divisions<br />
(Merrick and Schmida, 1984). <strong>The</strong> species is considered to be widespread and common<br />
throughout NSW, South Australia and Victoria in both inland and coastal drainages. It is<br />
common in coastal drainages of Queensland, is present in rivers draining into Lake Eyre, in<br />
parts of the Northern Territory and Western Australia, but has not been recorded from<br />
Tasmania (Allen 1989; McDowall 1996; Arthington et al. 1999). Arthington et al. (1999)<br />
observed that the species occurs in most aquatic habitat types in south-eastern Australia.<br />
Although there have been no systematic targeted surveys for gambusia in NSW, there have<br />
been a number of surveys, which have identified its presence. <strong>The</strong> most comprehensive fish<br />
survey undertaken has been the NSW Rivers Survey, during which 80 sites were surveyed<br />
over four periods from 1994 to 1996. <strong>Gambusia</strong> were recorded at 27 sites (see Appendix 2)<br />
11
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
with six sites having captures or observations of more than 50 individuals (Faragher and<br />
Lintermans 1997). <strong>The</strong>y were most widely distributed in the Darling and North Coast regions.<br />
<strong>Gambusia</strong> were also recorded at four sites in the South Coast and two sites in the Murray<br />
regions (Faragher and Lintermans 1997). <strong>The</strong>y were also found at altitudes of 20 to 1120m,<br />
although the majority of sites were below 300 m (Faragher and Lintermans 1997).<br />
Other surveys of fish in NSW include records of gambusia, at the Darling River anabranch<br />
(Callanan 1984) and in the Darling River (Callanan 1985), Wingecarribee River (Burchmore<br />
et al. 1990), Pindari Dam enlargement, Severn and Macintyre Rivers (Swales and Curran<br />
1995), the Macquarie River and its tributaries in the area of the Macquarie Marshes (Swales<br />
and Curran 1995a), the Cudgegong River (Swales et al. 1993), Gol Gol Swamp (Brown<br />
1994), the Hawkesbury-Nepean River system (Gehrke et al. 1999) and lower Balonne<br />
floodplain and Narran River (Mottell 1995). Lewis and Goldingay (1999) recorded gambusia<br />
at nine of fifteen coastal sites surveyed between Red Rock (40 km north of Coffs Harbour)<br />
and Ocean Shores (15 km north of Byron Bay). <strong>Gambusia</strong> has also been observed in<br />
numerous areas at Lake Macquarie on the Central Coast and in the Illawarra catchment and<br />
Sydney basin (Ross Wellington pers. comm.; Arthur White pers. comm.; Goldingay and<br />
Lewis 1999).<br />
While records of gambusia in the south coast area of NSW are limited, this does not<br />
necessarily mean that the species does not occur there. <strong>The</strong> presence of gambusia in the<br />
Snowy River catchment in Victoria was recorded during a survey of the lower Snowy River<br />
(Raadik et al. 2001). Recent surveys <strong>by</strong> Daly and Senior (2001) for the green and golden bell<br />
frog on the far south coast of NSW, between Batemans Bay and Eden, detected gambusia at<br />
15 of the 115 sites surveyed.<br />
6.1.1 Factors influencing distribution<br />
Factors influencing the distribution of gambusia in NSW include those directly and indirectly<br />
associated with humans, and also natural events such as dispersal through floods, via other<br />
animals, and those biological features of the species, which assist its dispersal in nature.<br />
Courtenay and Meffe (1989) suggested that gambusia fit seven of the criteria of a successful<br />
invader (identified <strong>by</strong> Ehrlich 1986) as follows:<br />
are abundant in original range<br />
are polyphagous<br />
have a short generation time<br />
a single female can colonise a new site<br />
have a broad physical tolerance<br />
are closely associated with humans, and<br />
have high genetic variability<br />
12
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Courtenay and Meffe (1989) proposed two additional criteria for success:<br />
specialised reproduction (ie high fecundity, highly developed young, reproduce numerous<br />
times per year, young are independent of adults after birth, the species is tolerant of broad<br />
range of temperature and day-lengths)<br />
females are extremely aggressive often causing the death of other species (Meffe 1985)<br />
6.2 Habitat Preferences<br />
<strong>Gambusia</strong> inhabit rivers, creeks, lakes, swamps and drains and occurs in both clear and<br />
muddy water (Cadwallader and Backhouse 1983). It has been able to invade a wide range of<br />
habitats including turbid, silty lower reaches of rivers, swamps, lakes, (including salt lakes<br />
and dystrophic systems of very low productivity in coastal dunes), billabongs, thermal<br />
springs, farm dams, the cooling pondage of a power station and ornamental ponds in many<br />
urban parks (Lloyd 1984; Lloyd et al. 1986; Arthington and Marshall 1999).<br />
Undisturbed lotic (ie flowing systems) with naturally variable discharge regimes are not<br />
favoured <strong>by</strong> gambusia. High river discharges almost eliminate populations (Meffe 1984;<br />
Arthington et al. 1990; Galat and Robertson 1992), perhaps because predatory efficiency is<br />
low, and long-term survival impossible (Reddy and Pandian 1974; Mees 1977; Lloyd et al.<br />
1986). Reddy and Pandian (1974) for example observed gambusia to be less efficient at<br />
preying on mosquito larvae in flowing waters.<br />
<strong>Gambusia</strong> has an ability to withstand adverse conditions, sometimes far beyond their normal<br />
tolerances. Lloyd (1984) noted that this enables gambusia to persist (though perhaps without<br />
breeding) in an unfavourable habitat before colonising other habitats. In laboratory<br />
experiments using gambusia, calm water was found to be the most important habitat variable,<br />
followed <strong>by</strong> submerged vegetation cover, which provides concealment from predators. Dense<br />
surface vegetation appears less favourable as it obstructs access to surface water where it<br />
forages. <strong>The</strong>se laboratory preferences indicate that gambusia actively seeks a suitable habitat<br />
in which it can compete successfully and be protected from predatory birds and fishes<br />
(Casterlin and Reynolds 1977; Lloyd et al. 1986).<br />
<strong>Gambusia</strong> are abundant in warm slow-flowing or still waters amongst aquatic vegetation at<br />
the edge of waterbodies in water depths of 10 cm or less (Merrick and Schmida 1984;<br />
McDowall 1996; Faragher and Lintermans 1997; Arthington et al. 1999). <strong>The</strong>y generally<br />
prefer warm water temperatures (>25C) (Lloyd 1984; Clarke et al. 2000), showing a thermal<br />
preference for water of 31C and thermoregulate during the day <strong>by</strong> moving from deep to<br />
shallow water (Winkler 1979). Populations are able to withstand wide temperature ranges<br />
from just above freezing (0.5C), to a critical thermal maximum of 38 (Lloyd 1984; Lloyd et<br />
al. 1986; Clarke et al. 2000). Populations have been known to survive for short periods of<br />
time in water temperatures as high as 44C (Lloyd 1984). Young gambusia are more resistant<br />
than adults to high temperature allowing them to colonise and exploit warm patches in the<br />
environment (Lloyd 1984). Females also appear to show more resistance to high water<br />
temperatures than males (Winkler 1975 cited in Lloyd et al. 1986).<br />
13
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Luna (2001) noted that the species tolerated a pH range of between 6.0 and 8.8, whereas<br />
Swanson et al. (1996) noted that a broader pH range of between 4.46 to at least 10.2 is<br />
tolerated based on both laboratory tolerance experiments and field observations. Additionally,<br />
Knight (2000) has observed gambusia occupying waters of pH 3.93.<br />
6.2.1 Use of modified habitats <strong>by</strong> <strong>Gambusia</strong><br />
Lloyd (1984) suggested that modified habitats are particularly susceptible to invasion <strong>by</strong><br />
gambusia due to these areas having relatively abundant sources of food, and low species<br />
richness because of harsh physical conditions. Arthington et al. (1990) developed this idea<br />
with examples from around Australia. <strong>The</strong> following summary identifies those aspects of<br />
habitat modification likely to be favoured <strong>by</strong> gambusia.<br />
River Impoundment<br />
Impoundment of water <strong>by</strong> dams or weirs can lead to reduced water discharge and slower<br />
flows. <strong>The</strong> subsequent development of shallow littoral zones, pools and areas of lentic habitat<br />
can facilitate growth of fringing vegetation. Such areas can provide very favourable habitat<br />
for gambusia. Arthington et al. (1983) observed that the proliferation of gambusia in the<br />
waterways of urban Brisbane corresponded to human induced changes, including construction<br />
of water-supply dams and flood retention basins, diversion of stream channels for flood<br />
mitigation, excavation of sand and gravel to form lentic habitat.<br />
Bank, riparian and channel alterations<br />
Degradation of riparian areas through agricultural and pastoral practices may lead to loss of<br />
riparian vegetation, bank erosion and collapse, sedimentation and river-bed alterations. <strong>The</strong>se<br />
are conditions which gambusia can tolerate to the disadvantage of native species (Arthington<br />
et al. 1990).<br />
Water quality and pollution<br />
Arthington et al. (1990) argue that the ability of gambusia to tolerate low dissolved oxygen<br />
concentrations has probably enabled the species to survive in areas such as stagnant urban<br />
drains, enriched ponds and eutrophic impoundments. <strong>Gambusia</strong> are able to utilise oxygen-rich<br />
surface layers of water, enabling them to survive in anoxic situations due to their dorsallyoriented<br />
mouth and flattened head (Lloyd 1984).<br />
Lloyd (1987) reviewed the tolerance of gambusia to pollutants and observed that the species<br />
was resistant to a wide range of pollutants, including organic wastes, phenols, pesticides,<br />
heavy metals and radiation. He observed that the species tolerance and resistance to pesticides<br />
is well known as it had been used in combination with pesticides to control mosquito larvae in<br />
rice fields in the United States.<br />
<strong>Gambusia</strong> are tolerant of a wide range of salinities, from very low salinity fresh water to<br />
marine conditions (McDowall 1996; Arthington and Lloyd 1989). <strong>Gambusia</strong> generally<br />
tolerate salinities of 25g/L in the field in the United States, but have been recorded in<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Australian salt lakes with salinities of 30g/L. Under laboratory conditions, most gambusia can<br />
tolerate salinities of 50g/L and some can survive 80g/L salinity conditions for short periods<br />
(seawater has a salinity of 35g/L) (Lloyd 1984).<br />
6.3 Breeding Biology, Social Organisation and Dispersal in Nature<br />
Sexual maturity<br />
<strong>Gambusia</strong> grow rapidly, becoming sexually mature in less than two months (McDowall<br />
1996). Immature male gambusia are sexually active well before their copulatory organ<br />
(gonopodium) has completely developed and before they are able to transfer sperm (Bisazza<br />
et al 1996).<br />
Fecundity<br />
Sexually mature females have been recorded as having up to nine broods a year from about<br />
August to April (Milton and Arthington 1983; McDowall 1996). On average, females have<br />
two or three broods per season, and store sperm between breeding seasons (Howe 1995; Lund<br />
1999a). Female gambusia may store sperm for up to eight broods or eight months and may<br />
nourish the live sperm within their reproductive tracts (Constantz 1989). Peak reproductive<br />
activity occurred in October in a population of gambusia studied near Brisbane, with 94% of<br />
females being pregnant at that time (Milton and Arthington 1983). <strong>The</strong> reproductive cycle is<br />
primarily governed <strong>by</strong> photoperiod, with reproduction ceasing once day length falls below<br />
12.5-13 hours, even when water temperature remains favourable (Lloyd 1986; Milton and<br />
Arthington, 1983; Pen and Potter 1991). <strong>Gambusia</strong> are live bearers (i.e viviparous), with<br />
fertilisation occurring internally and the embryos developing within the female (Cadwallader<br />
and Backhouse 1983; McDowall 1996). <strong>The</strong> gestation period is between 21 and 28 days, with<br />
about 50 young being produced on average, though broods may often exceed 100, with more<br />
than 300 having been reported in a single brood (Cadwallader and Backhouse 1983; Milton<br />
and Arthington 1983; McDowall 1996).<br />
Survivorship<br />
While the approximate sex ratio of young gambusia is initially 1:1, the subsequent higher<br />
mortality in males results in females usually dominating the adult population (Cadwallader<br />
and Backhouse 1983; Vargas and de Sostoa 1996). Males tend to disappear from populations,<br />
which may be due to their reproductive efforts and male fish being more susceptible to<br />
overcrowding and temperature stress than the females (Krumholz 1948 cited in Vargas and de<br />
Sostoa 1996). When female gambusia are pregnant their morphology changes and slower<br />
movements may render them more visible and therefore more susceptible to predators,<br />
skewing the sex-ratio in favour of males at this time (Vargas and de Sostoa 1996). <strong>The</strong><br />
maximum life span of up to two years occurs in females that do not mature until their second<br />
summer (Cadwallader and Backhouse 1983), although most will perish during winter (Lund<br />
1999a).<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Social organisation including behavioural characteristics<br />
<strong>Gambusia</strong> display a wide range of behaviours which enable them to adapt to a variety of<br />
situations (Lloyd 1984). In a study of the impacts of gambusia on the southern blue-eye<br />
(Pseudomugil signifer), no documented evidence of territoriality was found for gambusia.<br />
Territorial behaviour has not been observed in the family Poeciliidae of which gambusia is a<br />
member (Howe 1995). However, gambusia is known to show aggressive behaviour towards<br />
other fish species such as the southern blue-eye (P. signifer) (Howe 1995). Bisazza et al.<br />
(1996) found in experimental trials that adult males showed aggressive behaviour towards<br />
another male attempting copulation, irrespective of the maturity of the latter. <strong>The</strong> aggressive<br />
behaviour of gambusia toward fish species is discussed in detail in section 7.3.<br />
6.4 Diet and Factors Influencing Dietary Preferences<br />
<strong>Gambusia</strong> is an opportunistic omnivore with a preference for animal food (Rosen and<br />
Mendelson 1960; Al-Daham et al. 1977; Farley 1980 cited in Lloyd et al. 1986). <strong>Gambusia</strong><br />
select their prey according to size, colour, movement (Bence and Murdoch 1986; Lloyd et al.<br />
1986) position in the water column (Arthington and Marshall 1999) and availability (Lloyd<br />
1984). Arthington (1989) found that gambusia preferred small prey, a finding consistent with<br />
that of Bence and Murdoch (1986) who investigated size-selective predation <strong>by</strong> gambusia.<br />
<strong>The</strong>se two studies conflict with field studies <strong>by</strong> Wurtsbaugh et al. (1980) who suggested that<br />
gambusia generally select the largest prey they can successfully capture.<br />
<strong>Gambusia</strong> feeds on a diverse range of terrestrial insects such as ants and flies that fall onto the<br />
water’s surface, as well as aquatic invertebrates including bugs, beetles, fly larvae and also<br />
zooplankton (Lloyd et al. 1986; Arthington 1989; McDowall 1996). It is an adaptable<br />
generalist predator, able to vary its diet according to prey availability (Arthington 1989;<br />
McDowall 1996). <strong>Gambusia</strong> are diurnal visual feeders that feed during daylight hours and<br />
rely on sight to detect, track and attack prey (Swanson et al. 1996). In a study <strong>by</strong> Arthington<br />
and Marshall (1999) they found the diet of gambusia was composed of aquatic invertebrates,<br />
filamentous algae, terrestrial insects, arachnids, fragments of fruit and other plant tissues.<br />
More than 50% of the diet comprised items found at the water’s surface, such as chironomid<br />
pupae (midges), arachnids and terrestrial insects.<br />
<strong>The</strong>re is no direct evidence that frog eggs or tadpoles form a natural component of the diet of<br />
gambusia (Reynolds 1995), although the impact of gambusia on native frogs has been studied<br />
(eg Reynolds 1995; Morgan and Buttemer 1996; Webb and Joss 1997; Healey 1998; Gillespie<br />
and Hero 1999; Komak and Crossland 2000; Pyke and White 2000). Refer to section 7.4 for<br />
more information regarding the impacts of gambusia on frogs.<br />
6.5 Known and Potential Diseases, Predators and Competitors<br />
Disease and Parasites<br />
<strong>Gambusia</strong> has relatively few parasites in Australia when compared to North America (Lloyd<br />
1990). Swanson et al. (1996) has prepared a list of 23 of the most common and important<br />
parasites and pathogens of gambusia in the U.S.A. <strong>The</strong> only parasite observed on gambusia in<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
the lower Murray River (South Australia) is an exotic parasitic copepod, Lernaea cyprinacea<br />
(Lloyd 1984; Arthington and Lloyd 1989; Lloyd 1990). Another introduced parasite found in<br />
gambusia is a protozoan, Goussia piekarskii (Lom and Dykova 1995). Dove (1998) noted that<br />
11 parasites have been recorded in gambusia in Queensland.<br />
Predators<br />
In North America, predatory fish, wading birds, snakes and invertebrates have been found to<br />
prey on gambusia (Meffe and Snelson 1989). Swanson et al. (1996) list major predators of<br />
gambusia in the USA, as migratory and resident birds (herons, egrets, bitterns, grebes, ducks,<br />
kingfishers, terns, crows and blackbirds), piscivorous fishes (sunfish, catfish, bass), bullfrogs,<br />
and some aquatic insects including notonectids (backswimmers), corixids (water boatmen),<br />
dytiscids (predaceous diving beetles), and larval anisopterans (dragon flies).<br />
Predators of gambusia in Australia probably include birds, fish and even spiders (Lloyd<br />
1984). Many of the major predators of gambusia in the USA listed in Swanson et al. (1996)<br />
are also possible predators in Australia. Lloyd et al. (1986) noted important fish predators to<br />
include species of Anguilla, Mogurnda, Gobiomorphus, Leiopotherapon and Glossamia,<br />
although their impacts on gambusia are not known. Lloyd (1987) noted that water rats<br />
Hydromys chrysogaster and the fish eating bat Myotis adversus also apparently fed on<br />
gambusia. <strong>The</strong>re have been very few studies of predators of gambusia in Australia, but there<br />
have been suggestions as to the likely cause of low predation levels (Lloyd 1984). Both native<br />
and exotic fish predators avoid gambusia as prey when given a choice (Lloyd 1984; Lloyd<br />
1990). Reports suggest gambusia are considered unpalatable and that native predators may<br />
not have evolved behaviours appropriate to the capture of gambusia (Lloyd 1984). In inland<br />
lakes of NSW, little black cormorants (Phalacrocorax sulcirostris) feed mainly on exotic<br />
fishes such as carp and gambusia (Boulton and Brock 1999). Lloyd (1984) noted that, when<br />
exposed to predators, gambusia can rapidly develop complex escape and avoidance<br />
behaviours.<br />
Competitors<br />
Native fish species may compete with gambusia for food or other resources. Section 7.3<br />
includes discussion of the theory of competition in relation to gambusia and other species.<br />
Extensive dietary overlap occurs between gambusia and a number of native species.<br />
7. Impacts of <strong>Gambusia</strong> on Native Plants and Animals<br />
7.1 Impacts on Native Vegetation and River Health<br />
No forms of direct physical disturbance to aquatic environments, including to aquatic<br />
vegetation, appear to have been attributed to gambusia. <strong>The</strong> species does not exhibit obvious<br />
behaviours (such as carp disturbing aquatic vegetation while feeding), which may lead to<br />
habitat degradation.<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
7.2 Impacts on Macro-invertebrates<br />
Few studies have been undertaken concerning the impact of gambusia on invertebrates and<br />
the impact on threatened Australian invertebrates is not currently known. <strong>The</strong>re is some<br />
evidence that gambusia can cause reductions in populations of invertebrates such as rotifers,<br />
cladocerans, ostracods, copepods, mayflies, beetles, dragonflies and molluscs (Hurlbert et al.<br />
1972; Lloyd 1990a; Lund 1999b; Anstis 2002).<br />
Declines in some invertebrates may cause an increase in phytoplankton populations (Lloyd<br />
1990a). Stephanides (1964 cited in Hurlbert et al. 1972) observed a dramatic top-down effect<br />
of introducing gambusia to a small lake where fish had previously been absent; the<br />
elimination of zooplankton <strong>by</strong> gambusia caused a tenfold increase in phytoplankton<br />
populations. <strong>Gambusia</strong> may change invertebrate assemblages of ponds <strong>by</strong> differential<br />
predation, which can make a system unstable (Lloyd 1984). Lund (1999b) argued that these<br />
fish could potentially reduce water quality and could also increase the amount of algae in the<br />
water through excretion of nutrients. He suggested that in more pristine environments<br />
gambusia may eliminate rare taxa. In relation to mosquito control, Lloyd et al. (1986) argued<br />
that at low densities gambusia may actually encourage mosquito larvae <strong>by</strong> eating their<br />
invertebrate predators in preference to mosquitoes.<br />
Ecological attributes of macroinvertebrates that would make them susceptible to population<br />
level impacts from gambusia may include their method of reproduction, dispersal and<br />
migratory habits. Aquatic insects that have a terrestrial stage may be susceptible to predation<br />
<strong>by</strong> gambusia when undergoing the emergence stage of their life cycle (eg chironomid pupae -<br />
Arthington and Marshall 1999). Insects that deposit eggs on the water's surface may be<br />
susceptible to predation <strong>by</strong> gambusia if this occurs during times of the year when gambusia<br />
are at peak abundances.<br />
7.3 Impacts on Native Fish<br />
Worldwide Impacts<br />
Some thirty-five fish species worldwide have declined in abundance or range as a result of<br />
interactions with gambusia (Lloyd 1990). Lloyd (1987) provides a list of these species.<br />
Arthington and Lloyd (1989) considered that gambusia have been implicated in the extinction<br />
of small fish species in the USA, Asia and Africa and in the reduction in range or abundance<br />
of twenty-five species in the worldwide. In the USA, the replacement of a native fish species,<br />
the Sonoran topminnow (Poeciliopsis occidentalis) <strong>by</strong> gambusia is well documented (Galat<br />
and Robertson 1992). This native species was once widespread and abundant in desert areas<br />
and is now considered threatened due to habitat loss and predation <strong>by</strong> gambusia.<br />
Impacts on Australian Species<br />
While no local extinctions of fish species have been attributed to gambusia in Australia, this<br />
species may influence the distribution and abundance of particular native fish in areas where<br />
they co-occur (Arthington and Lloyd 1989). Howe et al. (1997) concluded that the ubiquity of<br />
gambusia has major implications for the conservation of several smaller species of fish in<br />
18
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Australia. In association with a range of environmental alterations, gambusia are thought to<br />
have played a role in the decline of fish species from six genera in Australia: Mogurnda,<br />
Ambassis, Melanotaenia, Pseudomugil, Craterocephalus and Retropinna (Arthington et al.<br />
1983; Lloyd 1990). However, Lloyd (1990) cautioned that much of the evidence was<br />
circumstantial and patchy.<br />
Lloyd (1984) argued that there is extensive overlap in requirements for food and space where<br />
populations of native fish and gambusia co-occur, and Arthington et al. (1983) demonstrated<br />
this in streams. Extensive dietary overlap has been documented between gambusia and at least<br />
seven native fish species, while two native species also show shifts in feeding niches, through<br />
expanding their feeding preferences, when living in association with gambusia (Lloyd 1990).<br />
Arthington and Marshall (1999) observed high dietary overlap between gambusia and the<br />
native ornate rainbowfish (Rhadinocentrus ornatus), and moderate dietary overlap with the<br />
native fire-tailed gudgeon (Hypseleotris galii). At some times of the year, gambusia switched<br />
its diet to feed on aquatic invertebrates usually eaten <strong>by</strong> these gudgeons, which increased the<br />
dietary overlap between the two species.<br />
In some areas of eastern Queensland, gambusia can dominate fish assemblages and may<br />
reduce the abundance and diversity of native species. McKay (1984) observed that in<br />
Queensland coastal streams where gambusia, guppies and swordtails occurred, native surface<br />
feeding or mosquito eating fish such as Melanotaenia, Pseudomugil, Craterocephalus and<br />
Retropinna were usually rare or absent. He noted the example of a significant decline in the<br />
southern blue-eye (P. signifer) at a site in the Brisbane River five years after gambusia and<br />
guppies had invaded.<br />
In creeks in the Brisbane area, Arthington et al. (1983) observed that large numbers of<br />
gambusia were correlated with small numbers of the native fire-tailed gudgeon (H. galii) and<br />
crimson-spotted rainbowfish (Melanotaenia fluviatilis), and that where they occurred together<br />
encounters were very likely. Arthington et al. (1983) noted that while the small populations of<br />
crimson-spotted rainbowfish (M. fluviatilis) may have been caused <strong>by</strong> habitat disturbance, the<br />
relationship between gambusia and fire-tailed gudgeon (H. galii) may have been due to<br />
interactions between these two species. <strong>The</strong>y suggested that the importance of interactions<br />
such as competition and predation may vary with the size structure of populations.<br />
<strong>The</strong>re is some evidence of predation and aggression <strong>by</strong> gambusia on native species.<br />
Investigation of gut contents of wild gambusia in NSW identified juveniles of Australian<br />
smelt, Duboulay's rainbowfish (Melanotaenia duboulayi), ornate rainbowfish (R. ornatus),<br />
southern blue-eye (P. signifer) and fire-tailed gudgeon (H. galii) (Ivantsoff and Aarn 1999).<br />
Fish remains were only identifiable up to 4 hours after feeding, which suggests that gut<br />
analyses may often underestimate many food items. Ivantsoff and Aarn (1999) noted that their<br />
study could not identify the significance of predation on native species <strong>by</strong> gambusia as newly<br />
hatched fish may be an important food source for fish species. In tank experiments, Howe<br />
(1995) observed gambusia to actively hunt and eat the young of southern blue-eye. Aarn<br />
(1998) suggested that in marginal eutrophic habitats where gambusia breed during the warmer<br />
19
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
months, high levels of predation of eggs and larvae may lead to the extinction of<br />
melanotaeniids (rainbow fishes). During monitoring of populations in January, in springs in<br />
central western Queensland, Wager (1995) suggested that the absence of juvenile red-finned<br />
blue-eyes (Scaturiginichthys vermeilipinnis) was probably due to predation of their eggs or<br />
fry <strong>by</strong> gambusia.<br />
<strong>Gambusia</strong> can exhibit aggressive behaviour towards other fish, including those much larger<br />
than themselves. This behaviour includes harassment such as chasing and fin-nipping, which<br />
may be so severe that fins are entirely removed (McKay 1984; Unmack and Brumley 1991;<br />
Steve Saddlier pers. obs.). In some instances, aggressive behaviour may also lead to<br />
secondary bacterial or fungal infections and eventual death (Faragher and Lintermans 1997;<br />
Knight 1999). Stress caused <strong>by</strong> aggression may also reduce breeding success as well as<br />
feeding and metabolic processes (Howe et al. 1997).<br />
Howe et al. (1997) argued that fin nipping may only occur in crowded conditions, such as<br />
with receding tides or prolonged drought conditions, where large numbers of fish occur in<br />
small ponds and waterholes. Howe et al. (1997) also suggested that the aggressive<br />
interactions observed may be a form of interspecific competition for space. Knight (1999)<br />
investigated interference competition between southern blue-eye (P. signifer) and gambusia.<br />
He found that under captive conditions, interference competition was density dependent and<br />
that gambusia inflicted stress and physical damage to the blue-eyes. Variations in aggressive<br />
behaviour were observed between individual fish, and males tended to attack more often than<br />
females. Further experiments under captive conditions have shown gambusia to exhibit<br />
aggressive behaviour towards ornate rainbowfish, (R. ornatus) Duboulay’s rainbowfish (M.<br />
duboulayi) and firetailed gudgeon (H. galii) (Jamie Knight pers. comm.).<br />
Lloyd (1990) indicated that there was some evidence that gambusia could affect growth rates<br />
of native fish species. In tank experiments, gambusia significantly affected both the growth<br />
and reproductive characteristics of southern blue-eye (P. signifer)(Howe et al. 1997). <strong>The</strong>y<br />
found that fish did not gain weight or grow in total length, their ovarian weight and fecundity<br />
were greatly reduced, and their ovaries were morphologically undeveloped. <strong>The</strong>se results<br />
clearly indicate that gambusia has the potential to significantly affect reproductive success as<br />
well as survival of this native species in confined habitats (Howe et al. 1997).<br />
Koster (1997) undertook tank experiments to determine whether gambusia affected the<br />
growth of native southern pygmy perch. His results indicated that under controlled conditions<br />
where food was not a limiting factor, gambusia did not affect the growth of the native species.<br />
In these tanks, gambusia nipped the fins of the southern pygmy perch as well as those of<br />
dwarf galaxias. However, this did not result in any infections or deaths of the native fish.<br />
Breen et al. (1989) also noted a total overlap in the diets of gambusia and dwarf galaxias.<br />
In some countries, hybridisation has occurred between gambusia species (Lloyd 1986). Howe<br />
(1995) points out that hybridisation between gambusia and native fish species is not possible<br />
as gambusia are live-bearers rather than egg laying fish.<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Impacts on Threatened Fish Species in NSW<br />
<strong>The</strong> NSW Fisheries Scientific Committee has identified gambusia as a possible cause of<br />
decline for the following threatened fish:<br />
Oxleyan pygmy perch (Nannoperca oxleyana) (Endangered species)<br />
Murray hardyhead (Craterocephalus fluviatilis) (Endangered species)<br />
Silver perch (Bidyanus bidyanus) (Vulnerable species)<br />
Western population of southern purple-spotted gudgeon (Mogurnda adspersa)<br />
(Endangered population)<br />
Western population of olive perchlet (Ambassis agassizii) (Endangered population)<br />
7.4 Impacts on Native Frogs<br />
<strong>Predation</strong> is generally recognised as a major factor regulating the distribution of amphibian<br />
tadpoles (eg Calef 1973; Heyer et al. 1975; Duellman 1978; Scott and Limerick 1983; Smith<br />
1983; Woodward 1983; Wilbur 1984; Hayes and Jennings 1986; Kats et al. 1988; Gillespie<br />
2001). Predatory fish are important determinants of tadpole species-composition (ie<br />
proportions of species present) and tadpole species richness (ie total number of species<br />
present) in both temperate (Hecnar and M’Closkey 1997) and tropical systems (reviewed <strong>by</strong><br />
Gillespie and Hero 1999). Many frog species avoid predation from fish <strong>by</strong> reproducing in<br />
habitats inaccessible to them, such as ephemeral pools or terrestrial microhabitats. Amphibian<br />
species that do reproduce in habitats naturally containing predatory fish invariably possess<br />
one or a combination of survival strategies to evade predation (Kats et al. 1988), such as<br />
cryptic colouration (Wasserug 1971), behavioural responses such as use of refugia (Sih et al.<br />
1988), schooling (Waldman 1982; Kruse and Stone 1984) and chemical defences (Liem 1961;<br />
Wasserug 1971; Brodie et al. 1978; Kruse and Stone 1984; Kats et al. 1988; Werner and<br />
McPeek 1994).<br />
Survival strategies tend to be predator specific and are unlikely to be effective against all<br />
predators. Palatability of a species of tadpole is not constant, varying according to the<br />
predatory fish species (Hero 1991; Holomuzki 1995; Gillespie 2001). <strong>The</strong>refore, the<br />
distribution of each tadpole species is related to the survival strategies it possesses and is<br />
strongly influenced <strong>by</strong> the distribution of predatory fish (Gillespie and Hero 1999).<br />
Tadpoles of native species may be able to evade predators with which they naturally coexist<br />
but may be unable to evade an introduced or new predator. <strong>The</strong>se species may not identify<br />
such fish as predators and hence fail to use the appropriate survival strategies (temporal or<br />
spatial isolation), or may not have the necessary anti-predator defences (eg cryptic<br />
colouration, behavioural responses such as refugia, schooling and chemical defences) that<br />
allow them to coexist with introduced fish species (Gillespie and Hero 1999; Gillespie 2001;<br />
Hamer et al. 2002). <strong>The</strong> introduction of a predatory fish species may result in the local or total<br />
extinction of some native prey species and a shift in the species composition of native frogs to<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
those species, which have the survival-strategies that allow them to coexist with the<br />
introduced predator (Gillespie and Hero 1999).<br />
<strong>The</strong> consequences of introducing fish into breeding habitats for frogs have been well<br />
documented overseas. A number of studies in Europe, North and South America have<br />
implicated or demonstrated that introductions of predatory fish are responsible for the decline<br />
or extinction of some frog species (see Gillespie and Hero 1999).<br />
Several studies in USA have demonstrated predatory impacts of gambusia on amphibians.<br />
Gamradt and Kats (1996) found that gambusia contributed to localised population declines of<br />
California newts (Taricha torosa) through predation on their larvae. Goodsell and Kats (1999)<br />
found that gambusia preyed heavily on tadpoles of Pacific tree frogs (Hyla regilla), both in<br />
natural streams and laboratory experiments, despite the presence of high densities of mosquito<br />
larvae as alternative prey.<br />
<strong>Gambusia</strong> may impact upon amphibian populations directly and indirectly <strong>by</strong>:<br />
predation of eggs and hatchlings<br />
predation of tadpoles<br />
aggressive behaviour causing tadpole tail damage or loss, which can result in increased<br />
risk of disease, increased risk of predation <strong>by</strong> other predators because of loss of mobility<br />
and reduced energy reserves and growth rates resulting in poorer post-metamorphic<br />
fitness<br />
aggressive behaviour causing changes in microhabitat use and activity patterns of tadpole,<br />
resulting in increased risk of predation <strong>by</strong> other predators or reduced growth rates<br />
<strong>The</strong> broad distribution and wide range of habitats occupied <strong>by</strong> gambusia in Australia means<br />
that this species may potentially impact upon many lentic and lotic frog populations over a<br />
large region. Gillespie and Hero (1999) reviewed the literature on interactions between<br />
gambusia and Australian amphibians. <strong>The</strong> following discussion is taken from this review,<br />
with the addition of more recently published information:<br />
A number of studies have identified negative associations between the presence of gambusia<br />
and frog species. Dankers (1977) found that tadpole numbers of several species were<br />
drastically reduced in ponds containing gambusia after early December in NSW, coinciding<br />
with a seasonal increase in fish biomass. McGilp (1994) found a negative correlation between<br />
the occurrence of the brown tree frog (Litoria ewingii) and that of gambusia in waterbodies<br />
along the Yarra River in Melbourne, Victoria.<br />
Reynolds (1995) found eggs of the sign-bearing froglet (Crinia insignifera) and Glauert's<br />
froglet (Crinia glauerti) to be unpalatable to gambusia. Preliminary trials also suggested that<br />
eggs of the slender tree frog (Litoria adelaidensis), Moore's frog (Litoria moorei) and<br />
Tschudi's froglet (Crinia georgiana) may also be unpalatable (Reynolds 1995). However,<br />
several studies have shown experimentally that gambusia are capable of preying on hatchlings<br />
22
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
and small tadpoles of a number of Australian frog species, such as the spotted grass frog<br />
(Limnodynastes tasmaniensis), Leseuer's frog (Litoria leseueuri) and bleating tree frog<br />
(Litoria dentata) (Harris 1995), sign-bearing froglet (C. insignifera) and Glauert's froglet (C.<br />
glaureti) (Reynolds 1995), green and golden bell frog (L. aurea) and bleating tree frog (L.<br />
dentata) (Morgan and Buttemer 1996), striped marsh frog Limnodynastes peronii and signbearing<br />
froglet (C. insignifera) (Webb and Joss 1997).<br />
Blyth (1994) compared survival and recruitment of tadpoles of three species of Western<br />
Australian frogs, Glauert's froglet (C. glaureti), sign-bearing froglet (C. insignifera) and<br />
moaning frog (Heleioporus eyrei), in the presence and absence of gambusia in experimental<br />
field enclosures. Tadpole survival of all species was significantly lower in the presence of<br />
gambusia at the end of the experimental period. However, the design of the enclosures<br />
allowed access for breeding <strong>by</strong> frogs from local frog populations, as evidenced <strong>by</strong> increases in<br />
numbers of frogs in some enclosures. Other potential predators of tadpoles also had access,<br />
such as invertebrates and birds. Furthermore, no species/fish treatments were replicated.<br />
<strong>The</strong>se factors limit interpretation of the results of this study.<br />
Webb and Joss (1997) examined frog species richness and abundance in relation to gambusia<br />
density and cover of emergent aquatic vegetation in ten ponds near Sydney. <strong>The</strong>y found a<br />
significant negative relationship between fish density and frog abundance but no relationship<br />
with frog species richness. <strong>The</strong> descriptions provided for each waterbody indicate high<br />
variability in habitat among pond sites. Unfortunately, additional factors such as pool size and<br />
native vegetation cover, which may strongly affect frog abundance, were not considered in<br />
their analyses. Tadpole density is easier to sample systematically than adult frog density in<br />
pond habitats (Heyer et al. 1994). Given that tadpoles are one of the life stages upon which<br />
gambusia potentially preys, a measure of the relative abundance of tadpoles, rather than that<br />
of frogs, may have provided a more reliable indicator of the impact of gambusia.<br />
Reynolds (1995) examined the occurrence of six frog species with gambusia in water bodies<br />
near Perth, Western Australia. In contrast to the above studies, he found no relationship<br />
between the presence/absence of gambusia and individual frog species, with one exception,<br />
the sign-bearing froglet (C. insignifera), which was found only infrequently together with<br />
gambusia. However, he observed that most of the sites used <strong>by</strong> the sign-bearing froglet (C.<br />
insignifera) were ephemeral and unsuitable for gambusia. Frog species richness was generally<br />
lower at sites occupied <strong>by</strong> gambusia, but many of these sites were also degraded, contributing<br />
to their unsuitability as frog breeding habitats.<br />
Reynolds (1995) also experimentally examined predation <strong>by</strong> gambusia on several tadpole<br />
species in Western Australia. Trials with tadpoles indicated that gambusia were able to attack<br />
and kill tadpoles of the slender tree frog (L. adelaidensis), Tschudi's froglet (C. georgiana)<br />
and moaning frog (H. eyrei). Controlled palatability experiments showed that survival of<br />
Moore's frog tadpoles was significantly reduced in the presence of gambusia. However,<br />
gambusia showed a strong preference for invertebrate prey (Daphnia sp. or mosquito larvae).<br />
Both groups were consistently consumed completely before tadpoles in all trials. In a field<br />
23
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
enclosure experiment, in which tadpoles were also exposed to invertebrate predators,<br />
Reynolds (1995) found no significant difference in survival in the presence or absence of<br />
gambusia. <strong>The</strong>se results, in conjunction with his field survey data, suggest that the impact of<br />
gambusia upon populations of these frog species is influenced <strong>by</strong> several factors, and under<br />
natural conditions may be limited.<br />
Webb and Joss (1997) conducted predation experiments examining the impact upon survival<br />
of different size classes of sign-bearing froglet (C. insignifera) and striped marsh frog (L.<br />
peronii) tadpoles <strong>by</strong> hungry and pre-fed gambusia. <strong>The</strong>y found significant differences<br />
between predation rates related to tadpole size class and hunger status of fish. Tadpoles of<br />
species which are able to rapidly attain moderate to large sizes, may therefore be less predated<br />
upon than tadpoles of other species (Caldwell et al. 1980; Crump 1984).<br />
Several studies have reported damage to the tails of larger tadpoles from gambusia attack<br />
(Dankers 1977; Blyth 1994; Harris 1995). This damage could result in reduced survival of<br />
larger tadpoles due to reduced mobility and feeding, inability to escape other predators, or<br />
reduced metamorphic fitness. However, some tadpole species have been found to survive tail<br />
loss (Harris 1995). Wilbur and Semlitsch (1990) reported tail regeneration <strong>by</strong> tadpoles of the<br />
American bullfrog (Rana catesbeiana) even after considerable loss, and suggest that this may<br />
be a general mechanism to reduce the impact of predation.<br />
Concerns for the role of gambusia in the decline of some frog species, particularly members<br />
of the bell-frog complex, have been expressed <strong>by</strong> several authors (Mahony 1993, 1999; Daly<br />
1995; Morgan and Buttemer 1996; White and Pyke 1996; White and Ehmann 1997; van de<br />
Mortel and Goldingay 1998; Goldingay and Lewis 1999; Lewis and Goldingay 1999;<br />
Biosphere Consultants Pty Ltd 2001; Daly and Senior 2001; Hamer et al. 2002). However,<br />
direct evidence linking gambusia to declines of frog populations in the ‘bell frogs’ is limited,<br />
due in part to conflicting findings and methodological limitations of some studies. For<br />
example, Morgan and Buttemer (1996) conducted controlled predation experiments<br />
examining the impact upon survival of tadpoles of green and golden bell frog (L. aurea) and<br />
bleating tree frog (L. dentata) <strong>by</strong> gambusia. <strong>The</strong> influence of aquatic vegetation on the<br />
predatory impact of gambusia was also examined. <strong>The</strong>y found that in the absence of aquatic<br />
vegetation, gambusia were able to significantly reduce tadpole survival of both species within<br />
24 hours. In the presence of aquatic vegetation, the effect was substantially reduced, and no<br />
significant impact of gambusia could be detected on the green and golden bell frog (L. aurea)<br />
after three days. However, survival of the bleating tree frog (L. dentata) was still significantly<br />
reduced after two days. <strong>The</strong>se findings indicate that presence of gambusia may significantly<br />
influence the survival of tadpoles, but that this is likely to be strongly influenced <strong>by</strong> habitat<br />
structure and tadpole behaviour. Green and golden bell frog (L. aurea) tadpoles have also<br />
been found occurring with native predatory fish (Graeme Gillespie pers. obs). In the absence<br />
of comparative data on the impact of these natural predators upon larval survival, it is difficult<br />
to assess the relative ecological significance of gambusia predation.<br />
24
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Pyke and White (1996) surveyed waterbodies in the Sydney region for green and golden bell<br />
frogs (L. aurea), and examined associations between evidence of breeding, occurrence of<br />
introduced fish, and habitat. <strong>The</strong>y found that breeding was most strongly associated with<br />
ephemeral rather than permanent or ‘fluctuating’ ponds, followed <strong>by</strong> the absence of<br />
introduced fish, primarily gambusia, and speculated that this fish was a major cause of decline<br />
of green and golden bell frogs. However, examination of their data reveals that pond<br />
permanency and occurrence of gambusia were highly correlated and so the results could also<br />
be explained in terms of unmeasured features of pond permanency and also abundance of<br />
other predators.<br />
Hamer et al (2002) however, has experimentally demonstrated that the growth of green and<br />
golden bell frog tadpoles is more favourable in permanent, rather than ephemeral water bodies<br />
and found that tadpoles did not respond to the presence of gambusia, making them more<br />
vulnerable to predation. <strong>The</strong> authors conclude that predation from gambusia may have<br />
reduced the suitability of permanent water bodies as optimal breeding habitat for green and<br />
golden bell frogs and that the long-term use of less favourable ephemeral habitats may have<br />
contributed to the decline of this species.<br />
White and Ehmann (1997) suggested that gambusia was also implicated in the decline of the<br />
yellow-spotted tree frog (Litoria flavipunctata), a closely related species to the green and<br />
golden bell frog. However, Osborne et al. (1996) point out that many of the sites from which<br />
this species has disappeared do not contain gambusia. Furthermore, both the green and golden<br />
bell frog (L. aurea) and southern bell frog (L. raniformis) (an ecologically similar species<br />
which occasionally hybridizes with the green and golden bell frog (L. aurea)) (Watson and<br />
Littlejohn 1985), have been recorded in abundance at some sites containing gambusia (van de<br />
Mortel and Goldingay 1998; Graeme Gillespie pers. obs.; Ross Wellington pers. obs.).<br />
In the USA, introduced fish have been implicated in the decline of the California red-legged<br />
frog (Rana aurora draytonii) (Hayes and Jennings 1986). However, Lawler et al. (1999)<br />
experimentally demonstrated that despite the widespread occurrence of gambusia throughout<br />
the former habitat of the California red-legged frog (R. aurora draytonii), predation from<br />
introduced American bull frogs (Rana catesbeiana) was likely to be a more substantial<br />
contributor to the decline of this species. In eastern Australia, gambusia are widespread and<br />
most abundant in disturbed habitats. To assess the role of gambusia in amphibian declines<br />
necessitates uncoupling of the impact of gambusia from other potentially threatening<br />
processes.<br />
Christy (2001) experimentally examined the cumulative effects of salinity and gambusia on<br />
the survival of tadpoles of the green and golden bell frog (L. aurea). She found an interaction<br />
between the effects of salinity and gambusia, which was far more detrimental to tadpoles than<br />
either factor in isolation. This study demonstrates significant synergistic effects between<br />
habitat quality and gambusia, which may have contributed to the decline of the green and<br />
golden bell frog (L. aurea) and related species such as the southern bell frog (L. raniformis).<br />
25
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
In summary, gambusia has been shown to kill or injure tadpoles, predate on frog eggs and<br />
exert some influence over frog habitat selection. However, conclusive evidence for gambusia<br />
having population level impacts on the abundance of Australian amphibians is yet to be<br />
clearly determined and is probably complicated <strong>by</strong> the cumulative effects of other threatening<br />
processes occurring at that time. Thus no absolute measure of the impact of gambusia on<br />
threatened frogs exists which may be used for prioritising management actions. So for this<br />
plan, an objective method for comparing the likelihood of impact between species was<br />
derived (Appendix 3). This model will then act as a means for prioritising the allocation of<br />
resources to gambusia control.<br />
<strong>The</strong> likelihood of impact on NSW frogs was modelled <strong>by</strong> comparing factors related to the<br />
susceptibility of a frog species to gambusia predation. <strong>The</strong>se factors were derived from those<br />
ecological attributes of frogs, particularly the egg and tadpole stages of the life cycle, that<br />
make them potentially vulnerable to impacts from gambusia. Factors included in the model<br />
were, habitat use, diet, fecundity, exposure/protection of eggs, length of larval period and<br />
anti-predator adaptations. <strong>The</strong>se factors were scored for all threatened and native frogs.<br />
Species with high scores are considered to be at higher risk of population level impacts from<br />
gambusia.<br />
<strong>The</strong> model identified four threatened species as most likely to be at risk from gambusia<br />
predation (Appendix 3). <strong>The</strong>y are the endangered green and golden bell frog (L. aurea),<br />
southern bell frog (L. raniformis) and yellow-spotted bell frog (L. castanea) and the<br />
vulnerable wallum froglet (Crinia tinnula). <strong>The</strong> ‘bell frog’ group of species have been<br />
identified <strong>by</strong> the NSW Scientific Committee determination process as well as <strong>by</strong> the scientific<br />
literature as species likely to be impacted <strong>by</strong> gambusia. Habitats containing key populations<br />
of these species will be considered as high priority for management intervention, including<br />
gambusia removal where feasible.<br />
Other threatened species such as the vulnerable olongurra frog (Litoria olongburensis) and the<br />
Nandewar and New England Bioregion endangered population of tusked frog (Adelotus<br />
brevis) had lower scores and are considered medium priority for gambusia control. <strong>The</strong><br />
remaining threatened species had a very low, or zero score from the model and are<br />
considered, at this stage, to be a low priority for management.<br />
A number of non-threatened native frog species were also identified as being at higher risk<br />
from gambusia predation. <strong>The</strong>y include species in the genera Litoria, Paracrinia and<br />
Limnodynastes, in particular the brown tree frog (Litoria ewingii), eastern dwarf tree frog<br />
(Litoria fallax), Perons tree frog (Litoria peronii) and Litoria tyleri, which are generally<br />
regarded as common and widespread in NSW (Appendix 3). For the purposes of this plan,<br />
these species will be considered of lower priority for targeted management intervention (ie<br />
actions that seek to remove gambusia from key sites) as they are less likely to experience<br />
population level impacts from gambusia predation than high risk threatened species.<br />
Nevertheless, these species are likely to benefit from the threat abatement actions proposed in<br />
the plan.<br />
26
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
7.5 Benefits to Native Plants and Animals<br />
<strong>The</strong> presence of gambusia has not been shown to provide any clear benefits to native plants<br />
and animals. However, some larger native fishes and birds may occasionally utilise them for<br />
food.<br />
8. Control of <strong>Gambusia</strong><br />
Very few documented control programs have been specifically targeted at gambusia, due<br />
mainly to the absence of control methods, which are both effective and specific for gambusia.<br />
<strong>The</strong> only effective control methods kill all fish species present and often other fauna species<br />
as well as gambusia. Chemical, biological and physical control measures trialed on gambusia,<br />
and other introduced fish such as carp, have been comprehensively reviewed <strong>by</strong> McKay et al.<br />
(2001). A brief summary is provided.<br />
Chemical Control<br />
Rotenone is a broad spectrum registered pesticide which is used as a garden insecticide. It is<br />
produced from the roots of several different plants, most commonly derris root, giving rise to<br />
the name ‘Derris Dust’. Rotenone has been used to control fish such as gambusia and carp. It<br />
can be applied to fish <strong>by</strong> suspension in water, <strong>by</strong> injection or <strong>by</strong> ingestion of an oral bait. In<br />
suspended form, rotenone enters the fish through the gills as the fish respire. It is carried<br />
through the entire body of the fish and causes the fish to suffocate because oxygen in the<br />
blood is not released to the tissues.<br />
Rotenone is not registered as a fish poison in Australia. It is toxic to most fishes and likely to<br />
impact on other species such as macro-invertebrates and possibly frogs, particularly at the egg<br />
and tadpole stages. It does break down into harmless <strong>by</strong>-products relatively quickly and has<br />
been used successfully in small, enclosed water bodies such as dams, farm dams and ponds<br />
(Meronek et al. 1996; Koehn et al. 2000). Rotenone has potential to be utilised in the creation<br />
of gambusia free supplementary habitat for certain frog species such as the green and golden<br />
bell frog (L. aurea), which utilises small permanent and ephemeral water bodies such as farm<br />
dams and ponds as breeding habitat.<br />
Lime and chlorine have also been used to control gambusia. However, neither are registered<br />
as fish poisons and both are also non-specific, killing most aquatic organisms. Dose rates and<br />
other impacts on non-target species require clarification.<br />
Biological Control<br />
<strong>Predation</strong> of gambusia <strong>by</strong> larger species is a control method, which is considered as one with<br />
high potential in the long-term control of gambusia. <strong>The</strong>re is, however, little (if any)<br />
quantitative data available to support this technique under natural circumstances. White<br />
(2001) suggested that mouth almighty (Glossamia aprion) may be a useful adjunct to fish<br />
poisons in eradicating gambusia from warm temperate ponds. Mouth Almighty (G. aprion) is<br />
a species native to coastal drainages of (possibly) northern NSW, Queensland, Northern<br />
27
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Territory, northern Western Australia and the southern rivers of Papua New Guinea<br />
(McDowall 1996). Appropriate stocking levels and potential impacts on tadpoles are not<br />
known and there would be significant risks associated with translocating this (and other)<br />
predatory species to locations outside of their normal ranges.<br />
Other biological control mechanisms such as the use of parasites, pathogens, bacteria and<br />
viruses have been proposed. However, more research is required to assess their effectiveness<br />
and impacts on native fauna. Research into molecular biology and biotechnology techniques<br />
to produce immuno-contraceptives or artificially enhanced pathogens that either kill or<br />
disable target species via the blocking of reproductive mechanisms may provide an effective<br />
future control method for gambusia. <strong>The</strong> Murray Darling Basin Commission is currently<br />
funding research into manipulating the genetic structure of carp to produce an inheritable<br />
‘daughterless carp’ (Murray-Darling Basin Commission 2002). <strong>The</strong> intent of the research is to<br />
reduce the long-term population of carp <strong>by</strong> restricting offspring to males. This research will<br />
initially be trialled on gambusia and therefore may have future benefits to the control of this<br />
species.<br />
Physical Control<br />
<strong>The</strong> most effective physical control method is likely to be the draining and drying of isolated<br />
habitats of specific frog species and the reduction of water levels to prevent access <strong>by</strong><br />
gambusia to all or parts of this habitat. This technique is feasible, particularly if the water<br />
level in the waterbody or wetland can be easily manipulated and the potential for<br />
reintroduction from either upstream or downstream can be controlled. <strong>The</strong>se practicalities will<br />
limit the size of waterbodies and wetlands that can be treated. <strong>The</strong> size and number of<br />
watercourses entering the waterbody will also be a significant constraint. Some of these<br />
waterbodies and wetlands may also rely on periodic inundation from near<strong>by</strong> watercourses,<br />
and the feasibility of restricting re-introductions of gambusia from these sources may be<br />
limited. <strong>The</strong> draining of these wetland areas has been used to successfully control gambusia in<br />
isolated ponds found in Alice Springs (McKay et al. 2001). Although it has been determined<br />
that the area must be dried out entirely as gambusia are able to survive relatively harsh<br />
conditions with little water for some time.<br />
Restoration of fully functioning ecosystems and ecological processes may be regarded as an<br />
indirect method of control. Human induced processes that modify or degrade natural<br />
environments can favour the establishment and subsequent domination of introduced species.<br />
<strong>The</strong> reversal of these processes is likely to benefit many native species (Arthington et al.<br />
1990). Known habitat preferences of gambusia appear to support this hypothesis. <strong>The</strong><br />
rehabilitation of ecosystem attributes such as habitat structure, stream bed contours, substrate<br />
type, flow regime, water quality, aquatic plants, riparian vegetation and connectivity between<br />
habitats should make habitat less favourable to gambusia and more favourable to native<br />
fishes. Many species of native fish would therefore be able to compete more effectively with<br />
gambusia. Ross Wellington (pers. comm.) reports that as part of a development approval<br />
process, artificial green and golden bell frog habitat were designed and installed with draining<br />
features to allow removal of water and thus facilitate on-going eradication of gambusia.<br />
28
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Public education can be focussed on publicising the impacts on the environment and native<br />
frog and fish species and reporting the presence of gambusia. <strong>The</strong> objectives of the public<br />
education would be substantial reductions in translocations and re-introductions of gambusia<br />
and increased knowledge of the existing locations of gambusia.<br />
9. Proposed Management of <strong>Gambusia</strong><br />
9.1 Introduction<br />
History suggests that the eradication of introduced fish is often impractical and almost always<br />
unsuccessful (Kailola 1990). This is likely to be the case with gambusia in Australia, where it<br />
occupies long stretches of inter-connected waterways and many other types of habitats across<br />
most of its range, and for which effective and species-specific control measures are currently<br />
lacking. For this reason, an integrated, targeted management strategy is proposed in this threat<br />
abatement plan, which seeks to contain the spread of gambusia and, where feasible,<br />
ameliorate the impacts of predation on threatened frogs <strong>by</strong>:<br />
minimising further human dispersal of gambusia through implementing enhanced<br />
government regulation, public education and awareness campaigns<br />
removing gambusia, where practical, from areas occupied <strong>by</strong> key populations of priority<br />
frog species<br />
creating supplementary gambusia-free habitat, adjacent to gambusia-inhabited<br />
<br />
populations of priority frog species, in areas where gambusia removal is considered not<br />
practical<br />
collaborating with broader water reform processes that seek to rehabilitate aquatic<br />
ecosystems and<br />
informing land managers <strong>by</strong> undertaking research into the biology and ecology of<br />
gambusia, its impacts on frogs and the efficacy of proposed control measures<br />
9.2 Threat Abatement Actions<br />
<strong>The</strong> broad objective of this plan is to ameliorate the impact of gambusia on frogs, particularly<br />
threatened frogs. This will be achieved through implementation of the actions identified<br />
below. Proposed actions are focussed on threatened frog species most likely to be impacted<br />
<strong>by</strong> gambusia and are both landscape and local in scale. Management of gambusia will be<br />
integrated with other natural resource management programs. <strong>The</strong> overall key performance<br />
criteria of this plan will be the increased viability of populations of key threatened frog<br />
species impacted <strong>by</strong> gambusia.<br />
29
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Objective 1: Minimise human dispersal of gambusia<br />
Humans have historically been considered a major mechanism for the spread of gambusia.<br />
Management actions then should be directed at minimising the influence humans have over<br />
increasing the range of this species. This may be achieved through increased regulation and<br />
enhanced public awareness of the ecological consequences of releasing gambusia into the<br />
environment. It is acknowledged that the dispersal of gambusia through natural events such as<br />
flooding or other animals, eg birds is unlikely to be prevented and impossible to manage.<br />
Action 1: Propose gambusia for declaration as a noxious fish in NSW<br />
<strong>The</strong> NPWS will liaise with NSW Fisheries to evaluate options and implications for the listing<br />
of gambusia as a noxious fish under the Fisheries Management Act 1994 (FM Act). A<br />
declaration of gambusia as noxious will prohibit the sale, possession and introduction of<br />
gambusia into any waters unless under the authority of a permit issued <strong>by</strong> NSW Fisheries. In<br />
addition, Fisheries Officers, under the FM Act will then have the power to seize, take<br />
possession of and destroy gambusia.<br />
A noxious declaration will also raise the profile of gambusia as a process threatening frogs in<br />
NSW and should benefit native frog species and other species such as freshwater fish and<br />
macro-invertebrates, which are also adversely impacted upon <strong>by</strong> the species. Media coverage<br />
and other public awareness actions will be implemented to accompany the proposed<br />
declaration. This action will be initiated within the first year of the plan.<br />
Action 2: Develop and disseminate education and awareness material<br />
<strong>The</strong> purpose of this action is to target those groups that may be responsible for, or have some<br />
association with, the maintenance and dispersal of gambusia in the environment. Groups to be<br />
targeted include:<br />
councils<br />
ornamental fish suppliers, keepers of aquarium fish and reptiles such as freshwater turtles<br />
property owners with farm dams<br />
school children and the<br />
general public<br />
NPWS will prepare and implement an education strategy that informs each target group about<br />
the poor record of gambusia as a mosquito control agent and the subsequent potential impacts<br />
of deliberately, or inadvertently dispersing gambusia into the environment. <strong>The</strong> strategy will<br />
also provide practical methods for landholders to restore frog habitat and where practical<br />
remove gambusia from a waterbody. Education and awareness resources for consideration<br />
include fact sheets, continued dissemination of diverse frog conservation information (such as<br />
the NPWS (2001a) ‘Helping Frogs Survive’ brochure), NPWS Internet displays and media<br />
interviews.<br />
30
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
NPWS will seek to collaborate with existing frog recovery projects and link with other<br />
government department initiatives (including those identified in Action 8 below) and interest<br />
group programs, which can assist with raising awareness about gambusia. <strong>The</strong>y include:<br />
DLWC, NSW Waterwatch and Bugwatch programs, Sydney Water Streamwatch program,<br />
NSW Fisheries, Department of Education Field Study Centres, Pet Industry Joint Advisory<br />
Council, Frog and Tadpole Society and the Australia New Guinea Fishes Association.<br />
<strong>The</strong> dissemination of educational material will be focussed on areas containing priority frog<br />
species most likely to be impacted <strong>by</strong> gambusia (refer to Objective 2, Action 4).<br />
Action 3: Prepare environmental assessment guidelines for consultants and consent<br />
authorities<br />
<strong>The</strong> NPWS will prepare advice to assist consultants, Councils and government agencies<br />
responsible for making an assessment or determination of the likelihood of a development or<br />
activity, which may result in the introduction of gambusia into an area occupied <strong>by</strong> threatened<br />
frogs or a change to existing interactions between gambusia and threatened frogs. This action<br />
is relevant to part (g) of the ‘eight part test’ (ie Section 95 of the EP&A Act) when deciding if<br />
a proposed development is likely to have a significant impact on the survival of threatened<br />
species, populations and ecological communities.<br />
Performance Criteria: Within the first year of the commencement of this plan, options for<br />
declaring gambusia noxious in NSW will be evaluated. Education and awareness material will<br />
be prepared and disseminated in the first two years of the plan. Within five years of<br />
commencement of the plan, public awareness of the issue and measures to mitigate ongoing<br />
human dispersal will be known amongst the target groups listed in actions two and three.<br />
Objective 2: Reduce impacts of gambusia on threatened frog species at key sites<br />
This component of the plan is directed at ameliorating the impacts of gambusia at the local<br />
scale. Actions are targeted at those threatened frogs, (ie green and golden bell frog (L. aurea),<br />
southern bell frog (L. raniformis), wallum froglet (C. tinula), olongurra frog (L.<br />
olongburensis) and the endangered population of tusked frog (A. brevis)) identified as being<br />
of high to medium risk of impact from gambusia. <strong>The</strong> yellow-spotted bell frog (L. castanea)<br />
has not been recorded since 1973 (NPWS 2001b). Actions for this species would be triggered<br />
when extant populations are located.<br />
Action 4: Survey threatened frog habitats for gambusia<br />
Surveys for gambusia, within and adjacent to habitats of high and medium priority threatened<br />
frog species will be conducted. Information from these surveys will improve our knowledge<br />
of the local distribution of gambusia in these habitats, particularly areas that are currently<br />
gambusia-free. Education and awareness resources identified in Action 2 can then be targeted<br />
to these areas, in an effort to prevent further human dispersal of gambusia.<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
NPWS will coordinate these surveys and where possible undertake them in conjunction with<br />
surveys proposed in future recovery plans for these threatened frog species. <strong>The</strong> support of<br />
volunteers or other groups collecting similar survey data will also be utilised where available.<br />
This action will be implemented within the first two years of the plan, with a follow up survey<br />
in year five.<br />
Action 5: Remove gambusia at key sites for high priority threatened species<br />
Total removal of gambusia from the environment is not feasible at this time. However,<br />
opportunities may exist to control gambusia at key sites for high priority threatened frog<br />
species.<br />
Selection of sites containing key populations of these species will be made in consultation<br />
with the relevant NPWS recovery plan coordinator. Each site will then be assessed to<br />
ascertain the practicality of removing gambusia. Sites that may be suitable for this action are<br />
small, enclosed waterbodies or isolated pools such as farm dams or drying creek beds where<br />
the likelihood of permanent gambusia removal is high and where the potential impacts to nontarget<br />
species from the control method(s) used are considered low.<br />
A pilot case study for each species will then be implemented to gauge the efficacy of the<br />
control technique and evaluate the response of the target species. If the control program is<br />
considered successful it will then be expanded to other suitable sites. Permission will be<br />
sought from land holders and relevant approval authorities prior to implementing any control<br />
measure such as draining a waterbody or applying a chemical treatment.<br />
NPWS will coordinate the implementation of this action.<br />
Action 6: Create gambusia-free supplementary habitat key sites for high priority threatened<br />
frog species<br />
At sites where the removal of gambusia is not considered practical, opportunities for the<br />
creation of supplementary frog breeding habitat will be evaluated. <strong>The</strong> intent of this action is<br />
to develop areas of gambusia-free habitat adjacent to existing gambusia-inhabited habitat in<br />
key population areas. Supplementary habitat may be ephemeral in nature or periodically<br />
drained to ensure it remains free from gambusia.<br />
Identification of suitable sites will be made in consultation with the relevant recovery plan<br />
coordinator and will be undertaken in conjunction with the evaluation of sites for removal of<br />
gambusia.<br />
NPWS will coordinate the implementation of this action.<br />
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Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Action 7: Monitor the response of threatened frog species to the creation of gambusia-free<br />
habitat<br />
NPWS will establish a rigorous monitoring program to measure the response of key<br />
threatened frogs at sites where gambusia is removed and where supplementary gambusia-free<br />
habitat is created. NPWS will undertake this action on an ongoing annual basis following the<br />
implementation of Actions 5 and 6 above.<br />
Performance Criteria<br />
Within two years of commencement of the plan, the presence or absence of gambusia in 75%<br />
of all habitats for high and medium risk frog species will be determined. In addition, within<br />
the life of the plan, programmes for the removal of gambusia and the creation of<br />
supplementary habitat for high priority threatened frog species will be established. <strong>The</strong><br />
response of threatened frogs to gambusia removal and supplementary habitat creation<br />
programmes will be measured at these sites and reported on at the completion of the plan.<br />
Objective 3: Integrate this threat abatement plan with other aquatic restoration<br />
programs<br />
Modified habitats are particularly susceptible to gambusia invasion and effective amelioration<br />
of the impacts of gambusia can only be achieved through the restoration of aquatic<br />
ecosystems at the landscape scale (see section 6.2). This threat abatement plan therefore needs<br />
to link with other broad-scale water reform processes that seek to address aspects of habitat<br />
disturbance favoured <strong>by</strong> gambusia such as river impoundment, declines in water quality,<br />
changes to natural discharge patterns, thermal regimes and bank and channel alterations.<br />
Action 8: Link this threat abatement plan to broad-scale water reform and river health<br />
programs<br />
Current government legislation and programs relevant to this action are described in Section 2<br />
of the plan and include:<br />
Water Management Act 2000<br />
Catchment Management Amendment Bill 2001 (not yet passed) and the Catchment<br />
Management Act 1989<br />
NSW Weirs Policy 1995<br />
<strong>The</strong> NSW Wetlands Management Policy 1996<br />
<strong>The</strong>re is no statutory requirement for threat abatement plans prepared under the TSC Act to be<br />
incorporated in, or implemented through the various legislative instruments described above.<br />
However, the NPWS is represented on various committees committed to implementing water<br />
reform programs and will advocate the importance of restoring aquatic ecosystems for the<br />
purpose of reducing the impacts of gambusia on frog species. Copies of this threat abatement<br />
plan will be provided to all relevant government agencies and committees responsible for<br />
river health and aquatic restoration programs.<br />
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<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
<strong>The</strong> NPWS will also seek to liaise with NSW Fisheries during the preparation of a future<br />
threat abatement plan for the listed key threatening process Introduction of fish to fresh waters<br />
within a river catchment outside their natural range as required <strong>by</strong> the FM Act.<br />
Performance Criteria:<br />
All relevant national and state government agencies and committees will receive copies of the<br />
plan in the first year of commencement. Contact with NPWS representatives participating on<br />
various water reform committees will be made and annual updates on the progress of the plan<br />
provided. Also information from these committees will be used to better implement this plan<br />
where possible.<br />
Objective 4: Increase knowledge of the general ecology of gambusia, its impact on native<br />
frog species and mechanisms for its control.<br />
Research is required to address gaps in the knowledge of the biology and ecology of<br />
gambusia, its impact on native species and the efficacy and impacts of proposed control<br />
measures. Information derived from these studies will assist in refining current management<br />
practices and/or develop new approaches to the control or removal of gambusia from the<br />
environment. Recommended areas of research are identified in the actions below. It is<br />
proposed that each of these actions be undertaken <strong>by</strong>, or in partnership with an academic<br />
institution or government research organisation eg NSW Fisheries.<br />
Action 9: Conduct investigations into factors limiting the establishment of gambusia in<br />
nature<br />
Proposed topics for research include:<br />
factors limiting the distribution and abundance of gambusia. Proposed studies would<br />
assess habitat preferences of gambusia to better understand factors, which influence their<br />
establishment and govern their rate of increase at a site<br />
comparing the distribution and abundance of gambusia in undisturbed and modified<br />
habitats to gain a better understanding of what habitat conditions influence their presence<br />
and<br />
identifying mechanisms of gambusia dispersal, to better understand how gambusia<br />
invades different habitats, particularly those likely to support frogs at risk from gambusia<br />
predation<br />
Action 10: Investigate the impacts of gambusia on frog species<br />
Evidence linking gambusia to declines in native and threatened frogs is currently<br />
inconclusive. Research is required to clarify the impacts of gambusia on frogs and to ascertain<br />
the role of gambusia in the decline of frog species assemblages in synergy with other<br />
processes that also threaten their survival eg frog chytrid fungus. This plan has identified a<br />
number of threatened and native frog species most susceptible to population level impacts<br />
from predation <strong>by</strong> gambusia (Appendix 3). Further research is also recommended into the<br />
34
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
palatability of frog eggs and tadpoles to gambusia, and the effectiveness of tadpole survival<br />
strategies in avoiding negative interactions with gambusia would also clarify the likely impact<br />
of gambusia predation on frog species.<br />
Action 11: Trial Rotenone as a gambusia control technique<br />
Rotenone has potential in certain circumstances to be an effective gambusia control agent<br />
(refer to section 8 of this plan). Trials will be undertaken to identify suitable dose levels and<br />
assess potential impacts to non-target species. Potential sites will be selected in consultation<br />
with the EPA and NSW Fisheries, and will be confined to small, enclosed waterbodies.<br />
An application for a research permit for the trials will be made with the National Registration<br />
Authority once suitable sites have been identified.<br />
Action 12: Monitor ongoing research into the control of gambusia<br />
<strong>The</strong> NPWS threat abatement plan coordinator will monitor ongoing advances in approaches to<br />
the management of pest species that may, or are being adapted to the management of<br />
gambusia eg Murray Darling Basin Commission funding of CSIRO research into<br />
‘daughterless carp technology’.<br />
Performance Criteria:<br />
Throughout the life of this plan, NPWS will seek partnerships and encourage research into the<br />
ecology of gambusia, its impacts on frogs and the development and efficacy of potential<br />
gambusia control measures. Relevant research outcomes will be incorporated into<br />
management.<br />
Objective 5: Ensure effective implementation of the threat abatement plan<br />
Implementation of this plan will require ongoing statewide coordination.<br />
Action 13: Provide support for the implementation of this plan<br />
Successful implementation of this threat abatement plan will require ongoing coordination<br />
through continued liaison with threatened frog recovery program coordinators, consultation<br />
with stakeholders such as NSW Fisheries, EPA, Local Councils, DLWC and individual<br />
landowners. <strong>The</strong> threat abatement coordinator will be responsible for overall implementation<br />
of threat abatement actions and communication of results of the plan to land management<br />
agencies, landholders and the public.<br />
Performance Criteria:<br />
Each of the actions identified in the plan will be initiated <strong>by</strong> the threat abatement coordinator<br />
within the prescribed timeframes (assuming funds for implementation are available). Progress<br />
toward objectives assessed <strong>by</strong> the performance criteria will be reviewed and updated in year<br />
five of plan.<br />
35
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
10. Economic and Social Impacts of the Plan<br />
<strong>The</strong> total cost of implementing the plan is estimated to be approximately $220,000 over five<br />
years. A breakdown of costs per action per year is provided in Appendix 4. Expected costs are<br />
approximations, which may require revision once actions are initiated. Some costs, identified<br />
in the plan may be partly absorbed <strong>by</strong> other recovery plans for threatened frog species or met<br />
<strong>by</strong> funding programs such as the NSW Biodiversity Strategy and Commonwealth<br />
Government Natural Heritage Trust. Approximately half the projected costs are attributed to<br />
research actions. <strong>The</strong> estimated cost of these actions may also be substantially reduced<br />
through the acquisition of a funding grant eg ARC Linkage Grant. Other economic impacts<br />
associated with implementation of this plan are likely to be minimal.<br />
<strong>The</strong> major social benefit of ameliorating the impact of predation <strong>by</strong> gambusia will be meeting<br />
the desire of many persons in the community to protect native frogs, particularly threatened<br />
species. Implementation of the actions proposed in the plan may also benefit other groups of<br />
native species such as fish and macro-invertebrates. No impact on Aboriginal heritage is<br />
expected. <strong>The</strong>re are unlikely to be any significant animal welfare issues related to this plan.<br />
Chemical control trials will be undertaken with the appropriate environment assessment,<br />
animal care and ethics and other relevant approvals to minimise non-target impacts.<br />
11. Review Date<br />
This threat abatement plan is to be formally reviewed <strong>by</strong> the NPWS in consultation with<br />
NSW Fisheries within five years of commencement of the plan.<br />
36
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
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Personal Communications<br />
Graham Gillespie - Department of Natural Resources and Environment, Victoria<br />
Jamie Knight – NSW Fisheries<br />
Jared Patrick - Pest Industry Joint Advisory Council<br />
Steve Saddlier - Department of Natural Resources and Environment, Victoria<br />
Ross Wellington - National Parks and Wildlife Service, NSW<br />
Arthur White – Frog and Tadpole Society of NSW<br />
Personal Observations<br />
Angela Arthington – Griffith University, Queensland<br />
Steve Saddlier - Department of Natural Resources and Environment, Victoria<br />
Graham Gillespie - Department of Natural Resources and Environment, Victoria<br />
49
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Appendix 1: NSW Scientific Committee Final Determination<br />
<strong>The</strong> Scientific Committee, established <strong>by</strong> the Threatened Species Conservation Act, has made<br />
a Final Determination to list <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> (<strong>Plague</strong> <strong>Minnow</strong>) as a KEY<br />
THREATENING PROCESS on Schedule 3 of the Act. Listing of Key Threatening Processes<br />
is provided for <strong>by</strong> Division 2 Part 2 of the Act.<br />
<strong>The</strong> Scientific Committee has found that:<br />
50<br />
1. <strong>Gambusia</strong> <strong>holbrooki</strong> Girard, 1859 (previously known as <strong>Gambusia</strong> affinis) (<strong>Plague</strong><br />
<strong>Minnow</strong>, also known as Mosquito Fish) is a small freshwater fish originally<br />
introduced into Australia in the 1920s. <strong>The</strong> fish was imported as an aquarium fish but<br />
some were released into creeks around Sydney, Melbourne and Brisbane.<br />
2. During the Second World War a government sponsored campaign was initiated to<br />
spread <strong>Gambusia</strong> <strong>holbrooki</strong> into as many east coast waterways as possible, as a<br />
control agent for mosquitoes.<br />
3. <strong>Gambusia</strong> <strong>holbrooki</strong> is an aggressive and voracious predator. Overseas research has<br />
documented its impact on fish, invertebrates and frogs. (Grubb, J.C. 1972. American<br />
Midland Naturalist 88, 102-8; Hurlbert, S.H., Zedler, J. & Fairbanks, D. 1972.<br />
Science 175, 639-41)<br />
4. Recent research has documented that <strong>Gambusia</strong> <strong>holbrooki</strong> preys upon eggs and<br />
tadpoles of the green and golden bell frog, Litoria aurea (Morgan, L.A. & Buttermer,<br />
W.A. 1996. Australian Zoologist 30, 143-149, White, A.W. & Pyke, G.H. 1998<br />
unpublished manuscript submitted to Australian Zoologist).<br />
5. Other studies have demonstrated that <strong>Gambusia</strong> also preys upon Litoria dentata<br />
(Morgan & Buttermer op.cit), Litoria lesueuri (White & Pyke, op.cit) and<br />
Limnodynastes peronii (Webb, C. & Joss, J. 1997. Australian Zoologist 30, 316-26).<br />
6. Presence of <strong>Gambusia</strong> <strong>holbrooki</strong> has been linked to the decline of Litoria aurea, the<br />
New England Bell Frog Litoria castanea, Southern Bell Frog Litoria raniformis, and<br />
the Southern Tablelands Bell Frog (Litoria sp.)<br />
7. Breeding <strong>by</strong> Litoria aurea is almost completely restricted to water bodies lacking<br />
<strong>Gambusia</strong> <strong>holbrooki</strong>.<br />
8. In view of 3, 4, 5, 6 above the Scientific Committee is of the opinion that <strong>Predation</strong><br />
<strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> is a serious threat to the survival of Litoria aurea and Litoria<br />
castanea, both species listed as threatened under the Threatened Species<br />
Conservation Act, and to other species of frog, and that predation <strong>by</strong> <strong>Gambusia</strong><br />
<strong>holbrooki</strong> is therefore eligible to be listed as a key threatening process because it<br />
adversely affects two or more threatened species and it could cause species that are<br />
not threatened to become threatened.<br />
Exhibition period: 29/1/99 - 12/3/99
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Appendix 2: NSW rivers survey records of <strong>Gambusia</strong><br />
Rivers and their catchments where gambusia have been recorded during the NSW Rivers<br />
Survey 1994-1996 (Faragher and Lintermans 1997).<br />
51
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Macquarie River Catchment<br />
Turon<br />
Little<br />
Talbragar<br />
Macquarie<br />
Bogan<br />
Duckmaloi<br />
Fish<br />
Namoi River Catchment<br />
MacDonald<br />
Peel<br />
Cockburn<br />
Hawkesbury River Catchment<br />
Cox’s<br />
Mangrove Creek<br />
Hunter River Catchment<br />
Hunter<br />
Goulburn<br />
Macleay River Catchment<br />
Gara<br />
Macleay<br />
Gwydir River Catchment<br />
Horton<br />
Gwydir<br />
Shoalhaven River Catchment<br />
Shoalhaven<br />
Murrumbidgee River Catchment<br />
Yass<br />
Colombo Creek<br />
Lachlan River Catchment<br />
Retreat<br />
Clarence River Catchment<br />
Clarence<br />
Orara<br />
Richmond River Catchment<br />
Richmond<br />
Leycester Creek<br />
Manning River Catchment<br />
Gloucester<br />
52
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Appendix 3: Development of a rank scoring system to predict<br />
gambusia impact on native frog species<br />
A model to rank the likelihood of population level impacts of gambusia predation on native<br />
frogs, including threatened species and endangered populations, has been prepared to guide<br />
management and better target threat abatement actions. Published scientific literature of the<br />
impacts of gambusia predation on frogs is relatively scarce, being predominantly restricted to<br />
a small number of species. However, it is acknowledged that frogs do possess ecological<br />
attributes that render them susceptible to predation and as a precaution, this plan advocates an<br />
adaptive approach to their management ie undertake some management intervention for those<br />
frogs species likely to have some population level impacts concurrent with ongoing research<br />
that seeks to clarify the existence and degree of impact.<br />
<strong>The</strong> model for the likelihood of impact is defined as:<br />
Sensitivity rating = (microhabitat score) x (dietary overlap + fecundity + exposure/protection<br />
of eggs + length of larval period + anti-predator avoidance)<br />
This model gives particular emphasis to microhabitat (multiplicative factor), so that those<br />
stages of the frog life cycle (ie their eggs and tadpoles) which occur in inaccessible habitats or<br />
habitats unlikely to be invaded <strong>by</strong> gambusia score zero.<br />
Threatened species comprise the first group of frogs in the accompanying table followed <strong>by</strong><br />
the remaining native frog species.<br />
Frog Microhabitat Use<br />
This factor describes the accessibility of frog eggs and tadpoles to predation and/or<br />
interference competition from gambusia. Frog species, which breed in habitat unlikely to be<br />
accessed <strong>by</strong> gambusia score zero.<br />
0 - Eggs and tadpoles occur in habitats inaccessible to gambusia. That is, where reproduction<br />
is totally terrestrial for all stages of the life cycle, or where the life cycle is partially aquatic<br />
but associated with water bodies unlikely to be colonised <strong>by</strong> gambusia (eg isolated ephemeral<br />
pools or high discharge first or second order streams).<br />
1 - Eggs and tadpoles are partially aquatic with gambusia having potential to opportunistically<br />
occupy habitats such as billabongs, farm dams or ox-bows through flooding or human<br />
dispersal.<br />
1 - Eggs and tadpoles are aquatic with a minimal chance of gambusia being present because<br />
they are not connected to permanent streams or waterbodies (eg ephemeral clay pans or sand<br />
dune swales etc).<br />
2 - Eggs and tadpoles are aquatic and occur in slow or moderate discharge third and fourth<br />
order streams with a reasonable chance of gambusia being present, or<br />
53
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
2 – Eggs and tadpoles are aquatic and are associated with a broad range of waterbody types,<br />
including flooded areas, permanent ponds and slow moving streams where there is a<br />
reasonable chance of gambusia being present in some of these habitats.<br />
3 - Those frog species whose life cycle occurs predominantly in permanent ponds, lentic<br />
interconnecting pools or slow flowing low altitude streams which gambusia can easily access.<br />
Dietary Overlap<br />
This factor describes the potential impacts of gambusia on frog species (essentially their<br />
tadpole stage) which have similar dietary preferences. Competition for food may occur in<br />
areas where resources are limiting.<br />
0 - None or minor overlap in diet ie tadpoles that are mostly herbivorous<br />
1 - High overlap in diet ie tadpoles that are predominantly macro-invertebrate or insect<br />
feeders<br />
Fecundity<br />
This factor describes the potential for frog species with a higher intrinsic rate of increase to<br />
compensate for mortality from gambusia predation on eggs.<br />
0 – High fecundity > 1000 eggs<br />
1 – Moderate fecundity of 500 to 1000 eggs<br />
2 – Low fecundity < 500 eggs<br />
Exposure/protection of eggs<br />
This factor describes the specific reproductive characteristics of frog spawn which place it at a<br />
higher risk of impact from predators. It assumes that frog species with foam egg masses are<br />
less vulnerable to predation than those with loose, simple egg masses.<br />
0 - Terrestrial egg mass not accessible to gambusia<br />
1 - Egg masses occur in aquatic habitat not easily accessible to gambusia eg in burrows,<br />
amongst litter, under rocks or on banks above water level.<br />
2 - Species with foam egg masses in aquatic habitats accessible to gambusia<br />
3 - Species with simple egg masses with loose eggs or clumps of eggs in exposed situations<br />
readily accessible to gambusia eg attached to submerged vegetation<br />
Length of larval period<br />
This factor describes the potential for frog species to be at higher risk of predation, if the<br />
aquatic stage of the life cycle occurs over a longer time frame.<br />
54
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
1 - Egg and tadpole periods less than 3 months<br />
2 – Egg and tadpole periods of approximately 3 months or greater<br />
Anti-predator adaptation<br />
This factor describes the potential for tadpoles to decrease the probability of predation<br />
through responses such as avoidance behaviour. Very little information is known on this<br />
factor, so scores are based on subjective opinion rather than known fact.<br />
0 – behaviour possibly effective in decreasing risk of predation eg schooling of tadpoles, or<br />
avoidance actions such as hiding amongst vegetation<br />
1 – no such behaviours currently known<br />
55
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Scientific name Common<br />
name<br />
Endangered<br />
Frogs<br />
Litoria aurea Green and<br />
Golden<br />
Frog<br />
Bell<br />
Litoria castanea Yellow spotted<br />
Tree frog<br />
Litoria raniformis Southern Bell<br />
Frog<br />
Mixophyes iteratus Giant Barred<br />
Frog<br />
Litoria<br />
booroolongensis<br />
Neobatrachus<br />
pictus<br />
56<br />
Booroolong<br />
Frog<br />
Painted<br />
Burrowing Frog<br />
Microhabitat Dietary<br />
Overlap<br />
Fecundity Exposure<br />
protection of<br />
eggs<br />
Length of<br />
larval period<br />
Anti-predator<br />
avoidance<br />
Sensitivity<br />
Ranking<br />
3 1 0 3 1 1 18<br />
3 1 0 3 1 1 18<br />
3 1 0 3 1 1 18<br />
2 1 0 1 2 0 8<br />
2 0 0 1 1 1 6<br />
1 0 1 3 1 1 6<br />
Litoria spenceri Spotted Frog 0 0 1 1 2 1 0<br />
Mixophyes fleayi Fleay's Barred<br />
Frog<br />
Pseudophryne<br />
corroboree<br />
Endangered<br />
Populations<br />
Adelotus brevis<br />
Nandewar and New<br />
England Bioregions<br />
Southern<br />
Corroboree Frog<br />
0 1 2 1 2 1 0<br />
0 1 2 0 2 1 0<br />
Tusked Frog 2 1 2 1 2 0 14
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Scientific name Common<br />
name<br />
Microhabitat Dietary<br />
Overlap<br />
Fecundity Exposure<br />
protection of<br />
eggs<br />
Length of<br />
larval period<br />
Anti-predator<br />
avoidance<br />
Sensitivity<br />
Ranking<br />
Vulnerable<br />
Frogs<br />
Crinia tinnula Wallum Froglet 3 0 2 2 1 1 18<br />
Litoria<br />
olongburensis<br />
Olongurra Frog 2 1 1 3 1 0 12<br />
Assa darlingtoni Pouched Frog 0 0 2 0 1 1 0<br />
Heleioporus<br />
australiacus<br />
Litoria<br />
brevipalmata<br />
Giant Burrowing<br />
Frog<br />
Green-thighed<br />
Frog<br />
Litoria littlejohni Littlejohn’s Tree<br />
Frog<br />
0 1 1 1 2 1 0<br />
0 0 2 3 1 1 0<br />
0 1 2 3 2 1 0<br />
Litoria piperata Peppered Frog 0 0 2 2 2 0 0<br />
Litoria<br />
subglandulosa<br />
Glandular Frog 0 0 2 2 2 0 0<br />
Mixophyes balbus Stuttering Frog 0 1 1 1 2 0 0<br />
Philoria<br />
kundagungan<br />
Mountain Frog 0 0 2 0 1 1 0<br />
Philoria loveridgei Loveridge's Frog 0 0 2 0 1 1 0<br />
Philoria<br />
sphagnicola<br />
Pseudophryne<br />
australis<br />
Pseudophryne<br />
pengilleyi<br />
Sphagnum Frog 0 0 2 0 1 1 0<br />
Red-crowned<br />
Toadlet<br />
Northern<br />
Corroboree Frog<br />
0 0 2 0 2 1 0<br />
0 0 2 0 2 1 0<br />
57
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Scientific name Common<br />
name<br />
Other native species<br />
58<br />
Litoria ewingii Brown Tree<br />
Frog<br />
Litoria fallax Eastern Dwarf<br />
tree Frog<br />
Litoria peronii Perons Tree<br />
Frog<br />
Microhabitat Dietary<br />
Overlap<br />
Fecundity Exposure<br />
protection of<br />
eggs<br />
Length of<br />
larval period<br />
Anti-predator<br />
avoidance<br />
Sensitivity<br />
Ranking<br />
3 1 1 3 2 1 24<br />
3 1 1 3 1 1 21<br />
3 1 0 3 2 1 21<br />
Litoria tyleri 3 1 1 3 1 1 21<br />
Litoria verreauxii 3 1 1 3 1 0 18<br />
Paracrinia<br />
haswelli<br />
Haswells Frog 2 1 2 3 2 0 16<br />
Litoria freycinetti Freycinet’s frog 2 1 2 3 1 1 16<br />
Limnodynastes<br />
dumerilii<br />
Crinia<br />
parinsignifera<br />
Eastern Banjo<br />
Frog<br />
Crinia signifera Common<br />
Eastern froglet<br />
3 1 0 2 2 0 15<br />
2 0 2 3 1 1 14<br />
2 0 2 3 1 1 14<br />
Crinia sloanei 2 0 2 3 1 1 14<br />
Litoria gracilenta Dainty Green<br />
Tree Frog<br />
2 1 1 3 1 1 14<br />
Litoria latopalmata 2 1 1 3 1 1 14<br />
Litoria<br />
pearsoniana<br />
2 0 2 2 2 1 14<br />
Litoria jervisiensis Jervis Bay Tree 2 1 1 3 1 1 14
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Scientific name Common<br />
name<br />
Microhabitat Dietary<br />
Overlap<br />
Fecundity Exposure<br />
protection of<br />
eggs<br />
Length of<br />
larval period<br />
Anti-predator<br />
avoidance<br />
Sensitivity<br />
Ranking<br />
Adelotus brevis<br />
Frog<br />
Tusked Frog 2 1 2 1 2 0 12<br />
Mixopheyes<br />
fasciolatus<br />
Great Barred<br />
Frog<br />
3 1 0 1 2 0 12<br />
Litoria nasuta Rocket Frog 2 1 0 3 1 1 12<br />
Litoria phyllochroa Leaf Green Tree<br />
Frog<br />
Litoria fletcheri Long-thumbed<br />
frog<br />
Litoria interioris Giant Banjo<br />
frog<br />
Litoria. peronii Brown-striped<br />
Frog<br />
Litoria salmini Salmon-striped<br />
Frog<br />
Litoria<br />
tasmaniensis<br />
Litoria<br />
terraereginae<br />
Spotted grass<br />
Frog<br />
Northern Banjo<br />
Frog<br />
2 0 2 3 1 0 12<br />
2 1 0 2 2 0 10<br />
2 1 0 2 2 0 10<br />
2 1 0 2 2 0 10<br />
2 1 0 2 2 0 10<br />
2 1 0 2 2 0 10<br />
2 1 0 2 2 0 10<br />
Uperoleia fusca 2 0 2 1 1 1 10<br />
Uperoleia<br />
capitulata<br />
Uperoleia<br />
laevigata<br />
2 0 2 1 1 1 10<br />
2 0 2 1 1 1 10<br />
Uperoleia tyleri 2 0 2 1 1 1 10<br />
59
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Scientific name Common<br />
name<br />
60<br />
Microhabitat Dietary<br />
Overlap<br />
Fecundity Exposure<br />
protection of<br />
eggs<br />
Length of<br />
larval period<br />
Anti-predator<br />
avoidance<br />
Sensitivity<br />
Ranking<br />
Uperoleia rugosa 2 0 2 1 1 1 10<br />
Litoria lesueuri Leseurs Frog 3 1 0 1 1 0 9<br />
Litoria ornatus Ornate<br />
Burrowing Frog<br />
Litoria citropa Blue Mountains<br />
Tree Frog<br />
Lechriodus<br />
fletcheri<br />
Neobatrachus<br />
centralis<br />
Neobatrachus<br />
sudelli<br />
Litoria rubella Desert Tree<br />
Frog<br />
Geocrinia<br />
victoriana<br />
2 1 0 2 1 0 8<br />
2 0 0 3 1 0 8<br />
Fletchers frog 1 1 2 1 1 1 7<br />
Trilling Frog 1 1 1 3 1 1 7<br />
1 1 1 3 1 1 7<br />
1 1 1 3 1 1 7<br />
1 0 2 1 2 1 6<br />
Notaden bennettii Crucifix Toad 1 0 1 3 1 1 6<br />
Cyclorana<br />
verrucosa<br />
1 1 0 3 1 1 6<br />
Cyclorana brevipes 1 1 1 3 1 0 6<br />
Cyclorana<br />
novaehollandiae<br />
Cyclorana<br />
alboguttata<br />
Striped<br />
Burrowing Frog<br />
1 1 1 3 1 0 6<br />
1 1 0 3 1 1 6<br />
Litoria caerulea Green Tree Frog 1 1 0 3 1 1 6
Threat Abatement Plan <strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong><br />
Scientific name Common<br />
name<br />
Litoria chloris Red-eyed tree<br />
frog<br />
Cyclorana<br />
platycephala<br />
Microhabitat Dietary<br />
Overlap<br />
Fecundity Exposure<br />
protection of<br />
eggs<br />
Length of<br />
larval period<br />
Anti-predator<br />
avoidance<br />
Sensitivity<br />
Ranking<br />
1 1 0 3 1 1 6<br />
1 1 0 3 1 0 5<br />
Crinia deserticola 0 0 2 3 1 1 0<br />
Pseudophryne<br />
bibronii<br />
Pseudophryne<br />
coriacea<br />
Pseudophryne<br />
dendyi<br />
Brown toadlet 0 0 2 0 2 1 0<br />
Red-backed<br />
Toadlet<br />
Litoria dentata Bleating Tree<br />
Frog<br />
0 0 2 0 2 1 0<br />
0 0 2 0 2 1 0<br />
0 1 0 3 1 0 0<br />
Litoria revelata 0 1 2 1 1 1 0<br />
61
<strong>Predation</strong> <strong>by</strong> <strong>Gambusia</strong> <strong>holbrooki</strong> Threat Abatement Plan<br />
Appendix 4: Threat abatement plan cost table<br />
Estimated costs of implementing the actions identified in this threat abatement plan.<br />
Action<br />
No:<br />
62<br />
Action Title Priority Estimated Cost/yr Total<br />
Cost<br />
Yr 1 Yr 2 Yr 3 Yr 4 Yr 5<br />
1 Proposal to declare<br />
gambusia as ‘noxious’<br />
2 Develop education and<br />
awareness tools<br />
3 Provide environmental<br />
assessment advice<br />
Responsible<br />
party/funding source<br />
1 $3500 $3500 NPWS $3500<br />
In-Kind<br />
Funds<br />
1 $3500 $7000 $3500 $14000 NPWS $7000 $7000<br />
1 $700 $700 NPWS $700<br />
4 Survey for gambusia 2 $2000 $3500 $3500 $9000 NPWS $9000<br />
5 Undertake targeted control 1 $6000 $5000 $5000 $16000 NPWS $10000 $6000<br />
6 Create supplementary<br />
habitat<br />
7 Monitor response of<br />
threatened frogs to<br />
gambusia removal<br />
8 Encourage and participate<br />
in broad scale river health<br />
programs<br />
9 Investigate factors limiting<br />
dispersal of gambusia<br />
10 Clarify impacts of gambusia<br />
on frogs<br />
11 Undertake chemical control<br />
trials<br />
12 Monitor progress of<br />
research<br />
1 $6000 $5000 $11000 NPWS $6000 $5000<br />
1 $8000 $8000 $8000 $24000 NPWS $15000 $9000<br />
2 $0 $0 $0 $0 $0 $0 NPWS<br />
2 $17000 $17000 $17000 $51000 NPWS, academic<br />
institution &/or other<br />
research institution<br />
2 $11000 $7000 $12000 $30000 NPWS, academic<br />
institution &/or other<br />
research institution<br />
2 $22000 $22000 NPWS, academic<br />
institution &/or other<br />
research institution<br />
2 $0 $0 $0 $0 $0 $0 NPWS<br />
13 Coordinate plan 1 $10500 $10500 $7000 $7000 $7000 $42000 NPWS $42,000<br />
Total $223,200 $93,200 $130,000<br />
Priority ratings are: 1- Action critical to meeting plan objectives, 2-Action contributing to meeting plan objectives. ‘In-Kind’ Funds represent salary component of permanent staff and current resources.<br />
‘Cash’ Funds represent the salary component for temporary staff and other costs such as travel and the purchasing of equipment.<br />
Recovery Plan Coordination includes all actions associated with ‘in-kind’ administration and general implementation of the recovery plan and is assumed to absorb costs associated with actions 8 and 12.<br />
Cash<br />
Funds<br />
$51,000<br />
$30,000<br />
$22,000