Introduced and native fishes in the Vasse‐ Wonnerup Wetland System and its rivers Beatty, S.J., Tweedley, J.R., Lymbery, A.J., Keleher, J, Allen, M.G., Morgan, D.L. Freshwater Fish Group and Fish Health Unit, Murdoch University August 2014 This project was supported by funding from the Australian Government’s Caring for our Country program Citations: Beatty S.J., Tweedley, J.R., Lymbery, A.J., Keleher, J, Allen, M.G., Morgan, D.L. (2014). Introduced and native fishes in the Vasse‐Wonnerup Wetland System and its rivers. Report to the Australian Government through its Caring for our Country Program. Freshwater Fish Group and Fish Health Unit, Centre for Fish and Fisheries Research, Murdoch University, Perth, Western Australia. Frontispiece: the Vasse floodgates and a large Goldfish removed from the lower Vasse River Native and Introduced Fishes of the Vasse‐Wonnerup 1 Table of Contents Acknowledgements ................................................................................................................... 3 Executive Summary ................................................................................................................... 4 Fish faunas of the rivers of the Vasse‐Wonnerup Wetland System ...................................... 11 Introduction ............................................................................................................................. 12 Materials and Methods ........................................................................................................... 14 Sampling locations and dates .................................................................................................. 14 Habitat and environmental variables ...................................................................................... 15 Spatial and temporal distribution patterns ............................................................................. 15 Movement patterns of freshwater fishes ................................................................................ 16 Introduced species removal ..................................................................................................... 16 Fin damage by Eastern Gambusia ........................................................................................... 16 Acoustic tracking of Goldfish ................................................................................................... 18 Results and Discussion ............................................................................................................ 23 Fishes and decapods in rivers of the Vasse‐Wonnerup ............................................................ 23 Spatial and temporal patterns in distribution ......................................................................... 24 Movement patterns of freshwater fishes ................................................................................ 31 Habitat and environmental variables ...................................................................................... 34 Introduced species removal ..................................................................................................... 38 Fin damage by Eastern Gambusia ........................................................................................... 40 Acoustic tracking of Goldfish ................................................................................................... 41 Summary .................................................................................................................................. 54 Fish faunas of the Vasse‐Wonnerup Wetland System ........................................................... 57 Introduction ............................................................................................................................. 58 Materials and Methods ........................................................................................................... 59 Sampling regime ...................................................................................................................... 59 Life cycle category and guild .................................................................................................... 62 Statistical analyses ................................................................................................................... 63 Results...................................................................................................................................... 67 Water quality ........................................................................................................................... 67 Overall number of species, density and life cycle category among regions ............................ 69 Numbers of species and density ............................................................................................... 73 Spatial changes in fish faunal composition .............................................................................. 75 Overall number of species, density and life cycle category among seasons and years ........... 89 Temporal changes in fish faunal composition ......................................................................... 93 Location of introduced fish captures ...................................................................................... 105 Discussion .............................................................................................................................. 106 Water quality ......................................................................................................................... 106 Number of species and density .............................................................................................. 109 Spatial changes in fish faunal composition ............................................................................ 111 Temporal changes in fish faunal composition ....................................................................... 114 Spatial and temporal changes the abundance and distribution of introduced fish .............. 115 Management and Monitoring Recommendations .............................................................. 118 References ............................................................................................................................. 123 Appendices ............................................................................................................................. 129 Native and Introduced Fishes of the Vasse‐Wonnerup 2 Acknowledgements The authors gratefully acknowledge the support and advice given to them throughout this study from the Vasse Wonnerup Pest Fish Steering Committee (VWPFSC), comprising: Jim Lane, Dr Kim Williams and Alan Clarke (Department of Parks and Wildlife), Dr Kath Lynch, Krish Seewraj and Jenelle Carter (Department of Water), Bruce Mackay, Michael Burgess, Claire Taylor (Department of Fisheries), Jen Mitchell (Geocatch), Dr Emily Hugues dit Ciles and Craig Bohm (South West Catchments Council) and Will Oldfield (Shire of Busselton). Sally Clifton Parks (Geocatch) is thanked for supporting the extension of this project, as are Vanessa Boladeras, James Florrison, Abbas Akbaripasand and Dr Joel Williams for their help with the fieldwork. Special thanks to the following landholders for kindly allowing access to their stretches of the various rivers: John and Janet Wells, Gary Bibby, Mark Nottle, Ross and Cheryl Manning, Peter and Donna Oates. This project was supported by the Australian Federal Government’s Caring for our Country program, GeoCatch and Murdoch University. A native Gilgie Cherax quinquecarinatus from the Abba River. Native and Introduced Fishes of the Vasse‐Wonnerup 3 Executive Summary The Vasse‐Wonnerup Ramsar Wetland System (VWWS) has international ecological significance due to its designation as a Ramsar site. However, the water quality is poor due in large part to high levels of nutrients which, in conjunction with other stressors such as regulation of flow, have caused numerous algal blooms and fish deaths. Surprisingly, there has been no quantitative research or monitoring of the fish communities in the VWWS despite fishes being key indicator group of ecosystem health and being a critical component in foodwebs and particularly for birds which give the system its Ramsar status. Although there has never been a comprehensive fish survey of the entire wetland, the adjoining rivers were known contain a number of introduced fish and crayfish species. As found elsewhere in south‐western Australia, these introduced fishes and crayfishes are known to impact directly on native fish species by predation and competition and indirectly by introducing exotic diseases. In addition, one of the key invasive species in the VWWS, Goldfish, is known to exacerbate algal blooms by re‐suspending nutrients and stimulating algal growth through their feeding processes. Other ecological impacts include alteration of natural food webs and habitat destruction through feeding and burrowing activities. The current project aimed to provide a comprehensive quantitative understanding of the fishes and crayfishes of the VWWS across the full range of habitats in order to assess the current and future health of the ecosystem and guide effective management decisions and monitoring programs. Given the impact of introduced fishes, the study had a specific simultaneous aim to document, prioritise and control introduced fishes and crayfishes to directly address a major known