Silver Perch

A Resource Document Volume 2 Pam Clunie & John Koehn Silver Perch: A Resource Document Pam Clunie and John Koehn Freshwater Ecology Arthur Rylah Institute for Environmental Research Department of Natural Resources and Environment 123 Brown Street, Heidelberg VIC 3084 tel: (03) 9450 8600 fax: (03) 9450 8730 July 2001 ISBN 978-1-74208-128-1 (Print) ISBN 978-1-74208-129-8 (Online) Final Report for Natural Resource Management Strategy Project R7002 to the Murray Darling Basin Commission Silver perch – A Resource Document The preparation of this publication was funded by the Murray Darling Basin Commission, Natural Resource Management Strategy and Department of Natural Resources and Environment, Victoria. The views expressed are those of the authors and do not necessarily reflect those of the Murray Darling Basin Commission. Copyright © 2001 Apart from fair dealing for the purposes of private study, research, criticism or review as permitted under the Copyright Act, no part of this publication may be reproduced by any means without the permission of Murray Darling Basin Commission. Acknowledgments The authors which to thank all staff of the Freshwater Ecology Group, in particular John McKenzie, John Mahoney, Damien O'Mahony, Louise Grgat, Tom Ryan, Jason Lieschke, Andrew Bearlin, Tim O'Brien, Simon Nicol, Steve Saddlier and Justin O'Connor. The authors also wish to thank Bill O'Connor and Julia Reed, Parks Flora and Fauna, Alan Baxter, Craig Balinger Fisheries, Department of Natural Resources and Environment, Brett Ingram, Geoff Gooley and Gus Strongman, Department of Natural Resources and Environment, Snobs Creek, Donna Tippett, Marine and Freshwater Resources Institute, Ray Mephan 'Little Valley', Alistair Dove University of Queensland, Jane Roberts CSIRO, Alex Hamlyn Department of Primary Industries, Andrew Sanger, Alan Lugg, Cameron Lay, Paul O'Connor, Craig Schiller, Ian Lyall NSW Fisheries, Deborah Love Department of Land and Water Conservation, Robyn Watts Charles Sturt University, Anthony Moore, Southern Cross University, Phil Cadwallader Queensland Fisheries Management Authority and Lance Lloyd Murray Darling Basin Commission, John Humphrey, Department of Natural Resources and Environment, John Winwood, formerly SA Recreational Fishing Council, Ross Hyne, New South Wales Environment Protection Agency and John Whittington, New South Wales Agriculture. Recovery Team Membership: • John Koehn, Manager, Freshwater Ecology, Arthur Rylah Institute for Environmental Research, Parks, Flora and Fauna, Department of Natural Resources and Environment • Pam Clunie, Freshwater Ecology, Parks, Flora and Fauna, Department of Natural Resources and Environment • Tarmo Raadik, Freshwater Ecology, Parks, Flora and Fauna, Department of Natural Resources and Environment • Dr Stuart Rowland, NSW Fisheries, Grafton, New South Wales • Dr John Harris, formerly NSW Fisheries, New South Wales • David Moffatt, Department of Natural Resources, Toowoomba, Queensland • Dr Michael Hutchison, Department of Primary Industries, Deception Bay, Queensland • Dr Clive Keenan, Department of Primary Industries, Bribie Island, Queensland • Dr Alistair Brown, Aquatic Ecosse, Melbourne, Victoria Freshwater Ecology, NRE & Murray Darling Basin Commission i Silver perch – A Resource Document • Linda Selg, Environment Australia • Bryan Pierce, South Australian Research and Development Institute Steering Committee Membership: • John Koehn, Manager, Freshwater Ecology, Parks, Flora and Fauna, Department of Natural Resources and Environment • Pam Clunie, Freshwater Ecology, Parks, Flora and Fauna, Department of Natural Resources and Environment • Brian Lawrence, Murray Darling Basin Commission, Canberra • Dr Alistair Brown, Aquatic Ecosse, Melbourne, Victoria. • Dr Martin Mallen-Cooper, Fishways Consulting Services, Sydney, New South Wales Freshwater Ecology, NRE & Murray Darling Basin Commission ii Silver perch – A Resource Document Summary This document outlines the existing biological information for silver perch Bidyanus bidyanus and reviews existing and potential threats to the species, including an assessment of their possible roles in the species' decline. It was prepared as the first step in developing a recovery plan for silver perch (Clunie and Koehn, in press). It is essential to understand the available knowledge and knowledge gaps when determining recovery actions for a species. This ensures that decisions can be made using the best possible information and that research efforts are not repeated unnecessarily. The collation of information for this project has indicated that silver perch has significantly declined within the majority of the Murray Darling Basin. Silver perch clearly warrants the formal recognition it currently has as a threatened species within Australia. There was a relatively consistent pattern of decline in commercial catches of silver perch in New South Wales since the early 1960s and in South Australia since the early 1980s. Many recent surveys within the Murray Darling Basin, including the New South Wales Rivers Survey, have recorded extremely low numbers of silver perch. Some surveys have indicated there has been a good population in the Murray River below Torrumbarry. The species' high fecundity means that in years were conditions are suitable, good recruitment and strong year classes are likely to be recorded. While this species has a wide distribution and was once abundant within the Murray Darling Basin, our knowledge of its habitat requirements and habitat preferences is poor. There have been some observations that the species prefers faster flowing, open waters, however the significance of habitat components such as woody debris, aquatic vegetation and riparian vegetation is unknown. Some research has been undertaken on movement patterns, indicating that both adults and juveniles undertake upstream movements. Upstream movements appeared to be stimulated by rises in water temperature and water level. Adults may move upstream prior to spawning. The reasons for upstream movement are not well understood. Whether there is variation in movement and spawning patterns across the species' range requires investigation. The behaviour, habitat preferences and physico chemical tolerances of eggs and larvae are also not well known. Silver perch has an omnivorous diet in which the significance of algal components appears to increase in adult fish. With the exception of high altitude habitats, silver perch naturally occurs throughout the entire Murray Darling Basin, an area which encompasses a wide range of climates, habitats and environmental conditions. There are numerous threats which exist across its range and various combinations of threats operate in different ways, over different areas and different timeframes. This resource document reviews threats in the following categories; river regulation, introduced species, water quality, instream and surrounding habitats, diseases, fishing and breeding and genetic issues. Many threats are closely interlinked and complex, making it difficult to distinguish between causes of decline and the effects of threats. Our knowledge of the distribution and severity of particular threats, Freshwater Ecology, NRE & Murray Darling Basin Commission iii Silver perch – A Resource Document as well as their impact on the aquatic environment and individual species is incomplete. The reviews of each threat outline background, management and an assessment of the significance of each threat. Some research has been undertaken on silver perch, however there is much we do not know of its ecological requirements or its response to many threats. There is no doubt the species has suffered a significant decline throughout the majority of its range, this decline occurring over many decades, but there is a lack of detailed information to provide an accurate pattern of decline for particular areas. How each threat specifically affects silver perch is also an important factor. For example, whether a threat causes sublethal or lethal effects and whether it affects each life history stage is crucial to understand. There is also often a time lag between the occurrence of a particular threat and when the ecological consequences are recognised. Since recent aging has indicated silver perch can live up to 27 years, the decline may be a result of changes and threats which occurred in the last 20-30 years. In this context, we cannot definitively state exact reasons for the decline of silver perch. It is likely that numerous threats have contributed to this decline, although some are clearly more significant and broad ranging than others. Threats such as river regulation have affected the majority of rivers within the Murray Darling Basin in a range of different ways. The changes to flow regimes may well have significantly affected the movement patterns and spawning success of silver perch. Barriers such as dams and weirs have restricted fish movements. Cold water pollution may have restricted successful reproduction as well as growth and survival for large stretches downstream of several major rivers. Barriers and thermal pollution are clear threats to silver perch. Whether carp has played any role in the decline of silver perch is unknown. It is not known how broad ranging threats such as sedimentation affect silver perch either in relation to adults, juveniles, larvae or eggs. Threats such as salinity may not have played a significant role in the decline of silver perch since the species demonstrates a reasonable tolerance to salinity.

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