Freshwater Catfish Recovery Plan

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

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• •

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

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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

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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. However this may become more significant in the future given the predicted increases in salinity over many areas. The toxicity of algal blooms is unknown. There are a number of other threats, such as predation by redfin or pesticide contamination which operate in specific parts of the Murray Darling Basin. These threats may have contributed to the decline of the species but are less broad ranging that threats such as river regulation. The susceptibility of silver perch to previous threats such as DDT is entirely unknown. Some research has been undertaken on the species' tolerance to endosulphan, a pesticide now commonly used. In comparison to a number of native and introduced species, silver perch was one of the least sensitive species to endosulphan, however sublethal effects of this pesticide have not been investigated. There are a number of diseases such as Epizootic Haematopoietic Necrosis virus and Viral Encephalopathy and Retinopathy which silver perch is susceptible to, however the prevalence of these viruses and other diseases in the wild, and whether silver perch may experience sublethal effects is unknown.


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Management issues such as stocking programs are likely to become more significant in the future, given the significant decline of silver perch. There are now large scale aquaculture operations, as well as releases of large numbers of silver perch fingerlings for put-and-take fisheries. The responsible management of genetic stocks is essential to ensure that if hatchery-reared stocks are released into the wild, they have appropriate genetic variation.


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CONTENTS ACKNOWLEDGMENTS............................................................................................................................. I SUMMARY.................................................................................................................................................III SECTION 1 EXISTING ECOLOGICAL INFORMATION ....................................................................1 1 INTRODUCTION .....................................................................................................................................1 2 DESCRIPTION .........................................................................................................................................2 2.1 TAXONOMY ...........................................................................................................................................2 2.2 GENETICS ...............................................................................................................................................3 3 DISTRIBUTION ........................................................................................................................................3 3.1 PAST DISTRIBUTION ...............................................................................................................................3 3.2 PRESENT DISTRIBUTION .........................................................................................................................5 3.2.1 South Australia ...............................................................................................................................5 3.2.2 Victoria...........................................................................................................................................5 3.2.3 New South Wales ............................................................................................................................6 3.2.4 Australian Capital Territory...........................................................................................................7 3.2.5 Queensland.....................................................................................................................................7 3.3 TRANSLOCATIONS ..................................................................................................................................8 3.3.1 Victoria...........................................................................................................................................8 3.3.2 New South Wales ............................................................................................................................8 3.3.3 Australian Capital Territory.........................................................................................................10 3.3.4 Queensland...................................................................................................................................10 3.3.5 Other States ..................................................................................................................................13 4 CONSERVATION STATUS AND LEGAL PROTECTION...............................................................14 5 BIOLOGY AND ECOLOGY..................................................................................................................16 5.1 GROWTH, LONGEVITY AND MATURITY ................................................................................................16 5.2 DIET .....................................................................................................................................................17 5.3 HABITAT PREFERENCE ..........................................................................................................................19 5.4 MOVEMENT ..........................................................................................................................................19 5.5 REPRODUCTION ....................................................................................................................................21 5.5.1 Spawning cues ..............................................................................................................................21 5.5.2 Spawning behaviour .....................................................................................................................21 5.5.3 Fecundity and spawning...............................................................................................................21 5.5.4 Larval growth ...............................................................................................................................22 5.5.5.Phototactic Responses ..................................................................................................................22 SECTION 2 - REVIEW OF THREATS....................................................................................................25 6 RIVER REGULATION...........................................................................................................................25 6.1 CHANGES TO FLOW REGIMES .....................................................................................................25 6.1.1 BACKGROUND ...................................................................................................................................26 6.1.2 MANAGEMENT...................................................................................................................................28 6.1.3 ASSESSMENT OF THE SIGNIFICANCE OF THE THREAT ..........................................................................30 Freshwater Ecology, NRE & Murray Darling Basin Commission

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Silver perch – A Resource Document 6.2 CHANGES TO TEMPERATURE REGIMES...................................................................................36 6.2.1 BACKGROUND ...................................................................................................................................36 6.2.2 MANAGEMENT...................................................................................................................................39 6.2.3 ASSESSMENT OF THE SIGNIFICANCE OF THE THREAT .........................................................................40 6.2.4 INCREASES IN WATER TEMPERATURE ...............................................................................................42 6.3 BARRIERS ............................................................................................................................................44 6.3.1 BACKGROUND ...................................................................................................................................45 6.3.2 MANAGEMENT...................................................................................................................................46 6.3.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ................................................................................50 7 INTRODUCED SPECIES .......................................................................................................................55 7.1 CARP......................................................................................................................................................55 7.1.1 BACKGROUND ...................................................................................................................................56 7.1.2 MANAGEMENT...................................................................................................................................58 7.1.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ................................................................................58 7.2 REDFIN..................................................................................................................................................65 7.2.1 BACKGROUND ...................................................................................................................................65 7.2.2 MANAGEMENT...................................................................................................................................66 7.2.2 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ................................................................................66 7.3 OTHER INTRODUCED FISH SPECIES ..........................................................................................69 8 WATER QUALITY .................................................................................................................................71 8.1 SEDIMENTATION...............................................................................................................................71 8.1.1 BACKGROUND ...................................................................................................................................71 8.1.2 MANAGEMENT...................................................................................................................................73 8.1.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ................................................................................73 8.2 SALINITY..............................................................................................................................................77 8.2.1 BACKGROUND ...................................................................................................................................77 8.2.2 MANAGEMENT...................................................................................................................................78 8.2.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ................................................................................79 8.3 ALGAL BLOOMS ................................................................................................................................84 8.3.1 BACKGROUND ...................................................................................................................................84 8.3.2 MANAGEMENT...................................................................................................................................86 8.3.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ................................................................................86 8.4 AGRICULTURAL CHEMICALS.......................................................................................................88 8.4.1 BACKGROUND ...................................................................................................................................89 8.4.2 MANAGEMENT...................................................................................................................................89 8.4.3 ASSESSMENT OF THE SIGNIFICANCE OF THE THREAT .........................................................................91 9 RIPARIAN VEGETATION ....................................................................................................................95 9.1 BACKGROUND ......................................................................................................................................95 9.2 MANAGEMENT......................................................................................................................................97 9.3 ASSESSMENT OF THE SIGNIFICANCE OF THE THREAT ............................................................................98 10 REMOVAL OF WOODY DEBRIS......................................................................................................99 Freshwater Ecology, NRE & Murray Darling Basin Commission

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Silver perch – A Resource Document 10.1 BACKGROUND ....................................................................................................................................99 10.2 MANAGEMENT..................................................................................................................................100 10.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ...............................................................................101 11 AQUATIC VEGETATION .................................................................................................................103 11.1 BACKGROUND ..................................................................................................................................103 11.2 MANAGEMENT..................................................................................................................................107 11.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ...............................................................................107 12 DISEASES.............................................................................................................................................108 12.1 BACKGROUND ..................................................................................................................................109 12.2 MANAGEMENT..................................................................................................................................113 12.3 ASSESSMENT OF THE SIGNIFICANCE OF THE THREAT ........................................................................113 13 AQUACULTURE INDUSTRY, TRANSLOCATIONS AND GENETIC IMPLICATIONS .......115 13.1 BACKGROUND ..................................................................................................................................115 13.2 MANAGEMENT..................................................................................................................................123 13.3 ASSESSMENT OF THE SIGNIFICANCE OF THE THREAT ........................................................................125 14 COMMERCIAL FISHING .................................................................................................................126 14.1 BACKGROUND ..................................................................................................................................126 14.2 MANAGEMENT..................................................................................................................................132 14.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ...............................................................................132 15 RECREATIONAL FISHERY.............................................................................................................134 15.1 BACKGROUND ..................................................................................................................................134 15.2 MANAGEMENT..................................................................................................................................135 15.3 ASSESSMENT OF SIGNIFICANCE OF THE THREAT ...............................................................................138 16 THREAT ASSESSMENT BY RECOVERY TEAM.........................................................................140 17 REFERENCES .....................................................................................................................................142 18 PERSONAL COMMUNICATIONS ..................................................................................................172


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Section 1 Existing Ecological Information 1 Introduction This resource document is presented in two sections. Section 1 includes a description of silver perch, outlines its past and present distribution, its conservation status and legal protection throughout the Murray Darling Basin, as well as our current state of knowledge on aspects of its biology and ecology. Section 2 provides a review of existing potential threats to the species and its habitat. Each review includes a background to the threat, a discussion of current management as well as an assessment of the significance of each threat to silver perch. Each review provides a summary of each threat. The resource document also includes an initial assessment of the significance of threats undertaken by the recovery team at the commencement of this project. Silver perch was once one of the most common fish species within the Murray Darling Basin. As is the case for many native fish species, detailed information concerning the past and present distribution of silver perch is limited, patchy and often anecdotal. However, it is apparent that the species has experienced a significant decline in distribution and abundance throughout most of its range. This observation comes from a collation of past and present survey data, the views of scientists, fisheries managers and anglers as well as commercial catch information. The collation of existing information of silver perch has indicated that while there has been some targeted research on the species, further research is required to fully understand the species' habitat preferences and requirements, the significance of threats to its aquatic environment, and the reasons for its recent decline in abundance and distribution. Some research has been carried out on Outline of research Much of the research carried out on silver perch relates to aquaculture. Little work has been undertaken concerning the species’ ecology, habitat preferences and requirements, the significance of threats to its aquatic environment, or reasons for its decline in abundance and distribution. Initial research was undertaken in the 1960s on reproductive biology, including inducement to spawn in rearing ponds (Lake 1967a) and morphogenesis and ontogeny (Lake 1967b). Following the recognition that silver perch has a high aquaculture potential (Lake 1967c), techniques for the effective hatchery production of silver perch have been developed; these are summarised by Thurstan and Rowland (1995). Detailed research has been carried out on artificial diet (Allan and Rowland 1992), diets in farm dams (Barlow et al. 1986), larval growth, development, behaviour and diet (Thurstan 1991), stocking success of different aged fish and marking of individuals (Willett 1993, 1994, 1996, Ingram 1993) disease (Rowland and Ingram 1991, Callinan and Rowland 1995) and water quality in intensive pond culture (Rowland 1995a). Silver perch has Freshwater Ecology, NRE & Murray Darling Basin Commission

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been found to be highly susceptible to the epizootic haematopoietic necrosis virus (EHNV) (Langdon 1989) and the Viral Encephalopathy and Retinopathy (VER) (Glazebrook 1995). Silver perch is also sensitive to low concentrations of the insecticide endosulphan (Sunderam et al. 1992). The tolerance of eggs and larvae (Guo et al. 1993) and juvenile fish (Guo et al. 1995) to varying levels of salinity have been tested, while Ryan et al. (1999) investigated the in situ tolerance of juvenile fish to high levels of salinity and low dissolved oxygen in stratified saline pools. The ability of larvae to detect and respond to gradients of light, depth, flow and leachates has been investigated (Gehrke 1990, Gehrke 1994). Reynolds (1983) carried out some work on movement patterns of adult silver perch, which recorded some undergoing extensive upstream migrations. Recent detailed research undertaken by (Mallen-Cooper et al. 1995) has found that both immature and adult silver perch undergo upstream movements. Mallen-Cooper (1994) investigated the ability of fish to negotiate an experimental fishway, although results were inconclusive. The population genetics of silver perch within the Murray Darling Basin has also been studied (Keenan et al. 1996).

2 Description 2.1 Taxonomy D.XII,12-13. P.14-17. A.III, 7-9. V.1,5. L.Lat. 70-90. Silver perch (Mitchell 1838) is a member of the family Terapontidae, which is a family restricted to the Indo-Pacific region (Merrick and Schmida 1984). There are fifteen genera in this large family of small to moderately sized perch-like fish. Similar species to the silver perch include welch’s grunter Bidyanus welchi and the barcoo grunter Scortum barcoo (Merrick 1996). The silver perch is also known as the grunter, black bream, silver bream, bidyan and Murray perch. It has an oval-elongate body which is highly compressed. The head is quite small and the snout pointed, appearing increasingly beak-like as size increases (Merrick and Schmida 1984). The eyes are small and located on the side of the head near the dorsal profile. The mouth is small, protractile, terminal and located ventrally; its gape reaches to approximately level with the posterior nostril. Narrow bands of small, pointed teeth occur along each jaw. The preorbital bone and preoperculum are strongly denticulate. The operculum has two flat spines, with the lower spine larger. Small, thin, ctenoid scales cover the body to the back of the head and preoperculum. A continuous lateral line follows the dorsal profile although it is not prominent. There is a single, longbased dorsal fin; the anterior section is spiny while the posterior section is soft. The dorsal fin is deeply notched between the spines, with only a small notch between the spiny and soft sections. The spines are longer than the rays, and depress into a groove along the dorsal surface. The anal fin has a short base with three strong spines and a soft ray section. A scaley sheath covers the bases of both the anal and dorsal fins. The pectoral fins are located low on the sides below the largest operculum spine. They are small and rounded. The pelvic spines are small and pointed, and positioned forward on the abdomen. The caudal fin is slightly formed, and the upper and lower lobes are pointed Freshwater Ecology, NRE & Murray Darling Basin Commission

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to slightly rounded (Cadwallader and Backhouse 1983). Shape can vary with age, with adults having a deeper and more compressed body than juveniles. While there is no sexual dimorphism, Lake (1967d) observed near ripe specimens to have a different body contour. Fish are dark grey to grey brown on the dorsal surface, silvery laterally, and lighter and close to white ventrally; the dorsal and caudal fins are grey while the pelvic fins are white (Merrick and Schmida 1984). Colour intensity can vary with water turbidity. The dark margins on the scales give a reticulated appearance. Fish smaller than 100 mm may be mottled, with vertical dark bars (Cadwallader and Backhouse 1983). Plate 2.1 Silver perch Bidyanus bidyanus

2.2 Genetics It is only recently that any research has been carried out on the population genetics of silver perch. Keenan et al. (1996) investigated the extent of genetic subdivision and inbreeding in populations of silver perch in rivers and impoundments within the Murray Darling Basin, using electrophoretic and morphometric techniques. Despite extensive sampling, only three polymorphic loci were identified. Another four loci showed unresolvable variability (C. Keenan, DPI, pers. comm. 1998). Three of the five stocked populations showed a reduced genetic variability compared to two wild populations and two other stocked populations. This limited genetic variation within some stocked populations was probably the result of hatcheries using small numbers of broodstock.

3 Distribution 3.1 Past Distribution The natural range of silver perch includes most of the Murray Darling drainage, excluding the cool, higher altitude, upper reaches of streams on the western side of Great Dividing Range (Merrick 1996). The species has been recorded in southern Queensland, western New South Wales, northern Victoria and South Australia (Cadwallader and Backhouse 1983). Previous records of the species from Western Australia and the Philippines are questionable and probably a result of misidentification (Vari 1978). Freshwater Ecology, NRE & Murray Darling Basin Commission

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Detailed information concerning the species’ distribution and abundance in the past within the Murray Darling system is limited. In his notes of an expedition along the lower Murray between 1856/57, Blandowski (1857) noted the presence of silver perch, including illustrations of three different forms that “.. are all difficult to distinguish from each other.” The illustrations appear to include a gravid female, a juvenile and an adult. In a NSW Fisheries book, Tenison-Woods (1883) observed that silver perch were “... found in all rivers of the Murray system”. In their revision of Australian Therapontids, Ogiliby and McCulloch (1916) include the following quote from a fisheries officer in New South Wales - “The silver perch is one of the most plentiful and important fishes of the western waters of New South Wales, and occurs in large numbers in the Murray River and many of its tributaries”. In 1949/50, J. O. Langtry carried out an ecological survey in the Murray Darling River system; this work was compiled for publication by Cadwallader (1977). The report indicated a range of sites where silver perch were recorded from, with some indications of abundance, as well as some catch data. Between 1938 and 1942, 11 530 silver perch were recorded passing through the Euston-Robinvale fish ladder. Cadwallader (1977) noted that prior to Langtry’s work, there was little information concerning the distribution of freshwater fish in south eastern Australia. Despite the lack of detailed information, anectodal evidence suggests the species was previously quite common. General texts such as Roughley (1951) noted that the species ”... is fairly abundant in the Murray River and most of its tributaries.” Grant (1978) indicated that silver perch was “... commonly caught in the inland streams and waterholes west of the Great Dividing Range”, while Scott et al. (1980) indicated that the species is “.. one of the most abundant fishes in the River Murray system...”. However, Reynolds (1976) observed the decreasing abundance of common native freshwater species, including silver perch, in the Murray River in South Australia. During a survey of the Murray River between Lake Hume and Lake Mulwala, Walker and Hillman (1977) noted that while they did not record silver perch, this species had been reported by local fishermen. During Langtry’s surveys in the late 1940s/early 1950s, he noted that silver perch occurred between Yarrawonga and Wangaratta, although there are no subsequent records on the Victorian Freshwater Fish Database. The Yarrawonga weir is likely to have prevented passage from the Murray River downstream. In Victoria, Cadwallader and Backhouse (1983) indicated that while silver perch was quite common in some areas, the species had recently experienced a significant reduction in range and abundance. In assessing the conservation status of freshwater species in northern Victoria, Brumley et al. (1987) considered silver perch to be locally abundant in lenthic and lotic sites in the Loddon River, while recognising the species was not widespread in northern Victoria. Brumley et al. (1987) indicated that there were probably fewer and smaller populations of silver perch than in the past, although they did not believe the species was threatened in the State. Pierce (1988) noted that historically the species had been widespread throughout the Murray Basin, but experienced major, possibly natural, population fluctuations. The reasons for these fluctuations are not well understood. Poole (1984) indicated that prior to Freshwater Ecology, NRE & Murray Darling Basin Commission

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river regulation, the abundance of fish in the Murray varied according to floods and drought. 3.2 Present Distribution The natural distribution of silver perch has changed since European settlement, due both to the decline in its abundance and distribution, as well as to the translocation of fish into various river systems, impoundments and private dams. Merrick and Schimda (1984) indicate that silver perch is not known upstream of Chinchilla on the Condamine River in southern Queensland, not beyond Bonshaw, New South Wales, on the Dumaresq River in the north east, or beyond Albury, New South Wales, on the Murray in the southeast, and Seven Creek and its junction within the Goulburn River in Victoria, to the south. It is apparent that the silver perch has suffered a significant decline in abundance and distribution within the Murray Darling Basin. A general map of the Murray Darling Basin including main tributaries is provided in Plate 3.1. 3.2.1 South Australia Limited information is available concerning the present status of silver perch in South Australia. Pierce (SARDI, pers. comm. 1998) believes the species can still be caught in most areas, although it has clearly declined in abundance. Surveys have indicated a dominant year class from the 1989 flood and no strong year classes since (B. Pierce, SARDI, pers. comm. 1998). 3.2.2 Victoria In Victoria, silver perch have been recorded from twelve river basins. These include eight basins where populations occur naturally - Upper Murray (Lake Hume stocking), Ovens River, Broken River, Goulburn River, Campaspse River, Loddon River, Murray Riverina and the Mallee. Silver perch have been introduced into the other four river basins Wimmera River, Yarra River, Werribee River and Corangamite. The majority of records are from the Goulburn River, Loddon River, Murray Riverina, and Mallee. In Victoria, records concerning the distribution and abundance of freshwater fish species are held within the Freshwater Fish Database, DNRE. In terms of silver perch, no surveys have specifically been undertaken to assess this species’ distribution and abundance in the state. Therefore, information within the Freshwater Fish Database is a collation of records from a variety of Departmental surveys as well as miscellaneous other records. These include Langtry’s surveys of the Murray in 1949/52, a survey of Sevens Creek by Cadwallader (1979), surveys around the Shepparton area during the Carp project (Hume et al. 1983), a survey of northern Victoria by Brumley et al. (1987) to assess the conservation status of native species, surveys by other Departmental staff, inland angling information compiled by Tunbridge and Rogan (1976), Tunbridge and Rogan (1981), Tunbridge et al. (1991) and Tunbridge and Glenane (1982) as well as more recent surveys along the Murray River (Koehn 1996, Koehn and Nicol 1998). Distribution and abundance information must be interpreted with care, taking into account gaps and concentrations in survey effort, survey methodology (e.g. nets used that Freshwater Ecology, NRE & Murray Darling Basin Commission

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may capture or fail to capture particular species, ages or sizes of fish), community composition (eg, some species may be far more abundant and dominant to catch) and the focus of surveys (stocking assessments, ecological surveys, presence/absence etc.). 3.2.3 New South Wales In New South Wales, Rowland et al. (1983) noted that while silver perch were found naturally in some impoundments, the majority of populations are small; they suggested this could be because of the absence of appropriate conditions for regular spawning and successful recruitment of larvae. The decline of silver perch is most effectively demonstrated by the comparison of numbers of silver perch caught at the top of the Euston fishway from 1939-1942 to 1987-1992. This indicates a decline of 93% in this area over the last 50 years (Mallen-Cooper and Brand 1992). The Murray River below Torrumbarry currently contains one of the largest populations (Mallen-Cooper et al. 1995). They suggest this maybe the result of the long distance (528 km) of river between Torrumbarry and the next weir downstream which is at Euston (Lock 15). Between February 1991 and June 1993, Mallen-Cooper et al (1995) estimated 7479 silver perch moved through the Torrumbarry fishway per week. There have been recent angling reports of silver perch being quite abundant near Torrumbarry (G. Gooley MAFRI, pers. comm. 1997) as well as near Barmah (J. McKenzie, DNRE, pers. comm. 2000). In the last year, large numbers of small sized silver perch have been recorded moving up through the fishway at Torrumbarry (J. McKenzie, DNRE, pers. comm. 2000). Keenan et al. (1996) surveyed a number of rivers and impoundments in the Murray Darling Basin to investigate the genetics of several species including silver perch. They only detected large populations of silver perch along the Murray River near the Torrumbarry Weir, and in the Warrego River in Queensland. A breeding population is also known from the Cataract Dam near Sydney. Recent surveys in the Murray Darling Basin indicate that silver perch numbers are currently extremely low throughout the Basin (Keenan et al. 1996). These have included surveys since 1990 to assess the impact of barriers on fish migration in the Darling River. Fish were sampled above and below the Bourke Weir; of the 9178 fish caught, only 7 silver perch were recorded, all downstream of the weir (Harris et al. 1992). A similar survey of fish above and below the Brewarrina Weir collected 922 fish; no silver perch were recorded (Mallen-Cooper and Thorncraft 1992). Sampling above and below the Main Weir at Menindee Lakes recorded 2819 fish, and again no silver perch were collected (Mallen-Cooper and Edwards 1991). Gehrke et al. (1996) surveyed nursery habitats in the Paroo catchment, the Darling River near Menindee, the Murrumbidgee River near Narrandera and the Murray River in the Millewa area. Catches of silver perch in these four catchments were extremely low. Of the more than 11 000 fish caught, only three were silver perch (Gehrke et al. 1995). The Rivers Survey in New South Wales has indicated that the species is in very low abundance in Darling/Barwon River (Harris et al. 1995). This extensive survey sampled 80 sites four times in two years. Only seven silver perch were recorded from the Darling region, and two fish (possibly stocked) in the Murray Region (Harris and Gehrke 1997). Freshwater Ecology, NRE & Murray Darling Basin Commission

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3.2.4 Australian Capital Territory The distribution of silver perch in the ACT has recently been reviewed by Lintermans (2000). Lintermans (2000) noted that the ACT probably represented the upstream limit of the species' distribution in the Murrumbidgee catchment. Numbers in the Canberra region have declined from the mid 1980s. A migration of silver perch moving upstream to the lower reaches of the Murrumbidgee River has not been recorded since the late 1970s/early 1980s. There are no records of silver perch from the Paddys, Naas or Gudgenby rivers and there are anecdotal angler records from the Molonglo River in the 1940s and 1950s. ACT Parks and Conservation Service (1995) notes that silver perch is "…now less common in the Murrumbidgee River than they were 15 years ago." 3.2.5 Queensland Few surveys have been undertaken in Queensland on the distribution and abundance of freshwater fish in the Murray Darling Basin. Midgely (1989) surveyed areas within the Lake Eyre and Bullo River Systems, as well as areas within the Murray Darling Basin such as the Warrego, Condamine and Balonne rivers. Silver perch was considered common at sites along the Condamine River (near Condamine), Warrego River (near Charleville) and Boorara Creek (near Hungerford), and rare along the Ward River (near Charleville) and Warrego River (near Cunnamulla). Midgely (1989) also noted that while he did not catch silver perch at Macintyre Brook near Inglewood, locals reported the species as being present. Keenan et al (1996) recorded low numbers of silver perch in most sites they surveyed in Queensland. A recent survey of landholders was undertaken in southern Queensland and northern New South Wales; the survey sought opinions concerning changes to the natural environment, including perceived declines in fish numbers (Mottell 1995). The following opinions were provided concerning silver perch: Table 3.1 Landholder opinions of the status of silver perch (taken from Mottell 1995). River

Year Last Seen

Abundant

Common

In Decline

Barwon Birrie Bokhara Culgoa Narran

1994 1993 1993 1994 1994

1 5 3 2 21

11 8 10 12 29

1 7 14 15

Non Existent

1 2

In Queensland, Hamlyn and Thomas (1995) observed that while there is a concerted stocking program primarily in impoundments within the Murray Darling basin, silver perch appear to be becoming increasingly scarce in rivers. About 850 000 silver perch have been stocked within the Queensland Murray Darling Basin since 1984. Stocking groups have generally found that stocking fingerlings into rivers provides poor returns and such stockings are now not favoured (D. Moffatt, DNR, pers. comm. 1998). Recent surveys have indicated that relatively abundant natural populations still exist in the Paroo and Warrego catchments. Silver perch also occurs incidentally in the CondamineBalonne and Border rivers catchments (D. Moffatt, DNR, pers. comm. 1998). Silver Freshwater Ecology, NRE & Murray Darling Basin Commission

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perch appear to be largely restricted to areas