OVERVIEW OF THE IMPACTS OF INTRODUCED SALMONIDS ON AUSTRALIAN NATIVE FAUNA

by

P. L. Cadwallader

prepared for the Australian Nature Conservation Agency

1996 ~~ AUSTRALIA,,)

Overview of the Impacts of Introduced Salmonids on Australian Native Fauna by P L Cadwallader

The views and opinions expressed in this report are those of the authors and do not necessarily reflect those of the Commonwealth Government, the Minister for the Environment or the Director of National Parks and Wildlife.

ISBN 0 642 21380 1 Published May 1996

© Copyright The Director of National Parks and Wildlife Australian Nature Conservation Agency GPO Box 636 Canberra ACT 2601

Design and art production by BPD Graphic Associates, Canberra Cover illustration by Karina Hansen McInnes CONTENTS

FOREWORD 1 SUMMARY 2 ACKNOWLEDGMENTS 3 1. INTRODUCTION 5 2. SPECIES OF SALMONIDAE IN AUSTRALIA 7 2.1 Brown trout 7 2.2 Rainbow trout 8 2.3 Brook trout 9 2.4 Atlantic salmon 9 2.5 Chinook salmon 10 2.6 Summary of present status of salmonids in Australia 11 3. REVIEW OF STUDIES ON THE IMPACTS OF SALMONIDS 13 3.1 Studies on or relating to distributions of salmonids and native fish 13 Grey (1929) Whitley (1935) Williams (1964) Fish (1966)

Frankenberg (1966, 1969) Renowden (1968) Andrews (1976) Knott et at. (1976) Cadwallader (1979) Jackson and Williams (1980) Jackson and Davies (1983) Koehn (1986) Jones et al. (1990) Lintermans and Rutzou (1990) Minns (1990) Sanger and F ulton (1991) Sloane and French (1991) Shirley (1991) Townsend and Growl (1991) Hamr (1992)

Ault and White (1994) McIntosh et al. (1994) Other Observations and Comments 3.2 Studies Undertaken During the Invasion of New Areas by Salmonids 21 Tilzey (1976) Raadik (1993) Gloss and Lake (in prep) 3.3 Experimental Introduction study 23 Fletcher (1978) 3.4 Feeding Studies, Including Analysis of Dietary Overlap and Competition, and Predation 25 Introductory Comments Morrissy (1967) Cadwallader (1975) Jackson (1978) Cadwallader and Eden (1981,_ 1982) Sagar and Eldon (1983) Glova (1990) Glova and Sagar (1991) Kusabs and Swales (1991) Crowl et at. (1992) Glova et al. (1992) Glova and Sagar (1993) Gillespie (1995) Other Observations and Comments 3.5 Behavioural Studies

31 Glova (1989) McIntosh et al. (1992) Edge et al. (1993) 3.6 Studies on the Disease Impacts of Salmonids 32 Introductory Comments Saville-Kent (1888) Parisot et al. (1965) Ashburner and Ehl (1973) Pollard (1974) Ashburner (1977) Whittington and Cullis (1988), Carson and Handlinger (1988) Langdon et al. (1988), Langdon (1989a, b) Davies (1991) 3.7 Overview of Studies on Impacts of Salmonids

36 4. CRITIQUE OF RESEARCH METHODS, RECOMMENDATIONS ON METHODS AND PRIORITIES FOR RESEARCH, AND MANAGEMENT ACTIONS 39 4.1 General Considerations 39 4.2 Review of Experimental Methods and Recommended Approaches for Investigating the Impacts of Salmonids on Native Fauna 39 4.3 Research Priorities 41 4.4 Management Actions 42 5. POLICIES AND REGULATIONS RELATING TO THE STOCKING OF SALMONIDS IN AUSTRALIA 45 5.1 Introductory Comments 45 5.2 Victoria 45 5.3 New South Wales 46 5.4 Australian Capital Territory 47 5.5 Tasmania 47 5.6 South Australia 47 5.7 Western Australia 48 5.8 Queensland 48 5.9 Future Directions 48 6. CONCLUSIONS AND RECOMMENDATIONS 51 7. BIBLIOGRAPHY 55 FOREWORD

This series of national overviews was commissioned by the Invasive Species Program to enable existing knowledge on the impact of introduced species on the natural environment to be collated and examined for key knowledge gaps. The impact of introduced animals on native species is an area that has been little studied in Australia. More often than not, the impact of introduced species is assumed rather than quantified. Five species of salmonids were introduced into Australia in the late 1800's. Since that time salmonids, particularly trout, have become widely distributed in certain areas of Australia and form a significant component of recreational fishing. However, in some places, at some times, salmonids can constitute a threat to populations of native fish, like the endangered Barred galaxias. This review on the impacts of introduced salmonids on Australian fauna is a comprehensive document providing excellent material for future research and planning for freshwater fisheries management. It is an invaluable contribution to the Australian Nature Conservation Agency's pursuit for information on the identified impacts of various introduced species and recommends a number of options to further investigate, clarify and contend with recognised impacts. I hope that it will be well utilised by all agencies and individuals concerned with biodiversity conservation.

Peter Bridgewater Chief Executive Officer Australian Nature Conservation Agency

1 SUMMARY

There have been few studies in Australia on the impacts of salmonids on fauna other than fish and those studies which have been done cover a relatively small part of the fish fauna. The most substantive evidence of impacts comes from an experimental introduction study and from observations made during the invasion of new areas. Much of the information on the distributions of salmonids and native fish is derived from surveys not specifically designed to investigate the effects of salmonids. The numerous and widespread instances of fragmented galaxiid distribution patterns in the presence of trout, the more widespread distribution of galaxiids in the absence of trout, and the fragmentation of galaxiid distribution pattern as trout move upstream, provide a substantial body of evidence for an adverse impact of trout on stream-dwelling galaxiids. The major impact of salmonids has been via predation. Salmonids have undoubtedly also had an impact via the spread of pathogens. Studies on the effects of salmonids on the distributions of native fauna should be designed specifically to test the hypothesis that the occurrence of a particular species is affected by the presence of salmonids. Introduction experiments in the field provide the most convincing evidence of an impact. Salmonids are implicated in the demise of ten of Australia's threatened fish species. Priority should be given to research on the threatened galaxiids, pygmy perches and Australian grayling. Reserves for all Tasmanian galaxiids should be established. The impact of trout on macroinvertebrates and aquatic vertebrates other than fish has been largely ignored and requires urgent assessment. The value of salmonids as sport-fish and in aquaculture has overshadowed consideration of their effects on native fauna and, in general, legislation to safeguard native fauna from the effects of salmonids is lacking. The agencies responsible for the management of salmonid fisheries need to re-assess their attitudes and take a more pro-active approach to protecting native fauna.

Disclaimer Funding to compile this report was provided by the Australian Nature Conservation Agency (ANCA) under the Invasive Species Program. The views expressed in this report are not necessarily those of ANCA.

1 ACKNOWLEDGMENTS

I thank John Hicks, Jim Barrett and Narelle Montgomery of the Australian Nature Conservation Agency for their help in setting up the project and for guiding it through to completion; Noel Morrissy of the Fisheries Department of Western Australia, Wayne Fulton of the Inland Fisheries Commission of Tasmania, Nigel Forteath of the Department of Aquaculture of the University of Tasmania, Gary Henry of NSW Fisheries, Alan Baxter of the Victorian Department of Conservation and Natural Resources (VDCNR), Don Mackie of the South Australian Department of Primary Industries, Bryan Pierce of the South Australian Research and Development Institute, Peter Reiman of the South Australian Fly Fishers' Association, Mark Lintermans of the ACT Department of the Environment, Land and Planning, and Peter Jackson of the Queensland Department of Primary Industries (QDPI) for providing information on the impacts of salmonids or on stocking policies and regulations in relation to salmonids; Sue Palmer, librarian at the Victorian Fisheries Research Institute, VDCNR, for conducting the electronic literature search and for providing reference material; Zena Seliga, QDPI librarian, Peter Grant of the Snobs Creek Freshwater Fisheries Research Station and Hatchery, John Humphrey and Mark Crane of the Australian Animal Health Laboratory, and Grant Rawlin of the Victorian Institute of Animal Science for providing reference material; Gerry Closs of the Department of Environmental Management and Ecology of La Trobe University for making available unpublished material; Colin Townsend of the Department of Zoology of the University of Otago, New Zealand, Tarmo Raadik of the Arthur Rylah Institute for Environmental Research, VDCNR, John Harris and Bob Faragher of NSW Fisheries, Noel Morrissy, John Humphrey and Wayne Fulton for their constructive comments on an early draft of the manuscript and for providing new material or drawing my attention to other relevant material.

1. INTRODUCTION

Habitat degradation is recognised as a major • review policies and regulations relating to factor in the decline of Australia's native the introduction and stocking of freshwater and estuarine fauna. In particular, salmonids from the perspective of impact the importance of sustaining fisheries by on native fauna; and sustaining fish habitat is well recognised ( • provide a comprehensive bibliography. Hancock 1992). However, even though habitat A priori it must be assumed that the degradation has had a major impact on the introduction of any species will have an impact range and abundance of many native as far as the native fauna is concerned ( freshwater fish species, introduced fish are Cadwallader 1978). As pointed out by Taylor et also implicated in the demise of several species al. (1984), defining "impact" as any effect on a (Pollard and Burchmore 1986, Ingram et al. native population attributable to an introduced 1990, Jackson 1993, Jackson et al. 1993, species deems its occurrence a foregone Wager and Jackson 1993). conclusion; that no effects should result from Earlier reviews of the effects of introduced fish such perturbations strains ones's confidence on Australian native fauna by Butcher (1967), in ecological principles. With few exceptions, Weatherley and Lake (1967), Cadwallader ( research and comment on the impact of 1978), Tilzey (1980), McKay (1984), Fletcher ( salmonids on the freshwater and estuarine 1986), Morison (1988), Arthington (1989), fauna of Australia has been focused on the Pollard (1990) and, specifically of the effects of fish fauna. Jackson (1981) provided a list of salmonids, by Jackson (1981) and, more the native fish (together with their maximum recently, Crowl et al. (1992) and Keam (1994), recorded lengths) which occur in trout waters have highlighted the paucity of hard evidence in south-eastern Australia. Theoretically, in relation to the demonstration of an impact of members of the following fish families, all of introduced salmonids on Australian native which occur in waters in Australia in which fauna. salmonids have been introduced, could be The purpose of this report is to: affected at some stage of the their life cycle by • provide a summary of the introduction of salmonids: Petromyzontidae, Anguillidae, salmonids into Australia, the species Galaxiidae, Retropinnidae, Prototroctidae, present, their distribution, utilisation and Aplochitonidae, Gadopsidae, Nannopercidae, biology; Bovichthyidae, Teraponidae, Percichthyidae, • review research findings on the impacts of Eleotridae and Gobiidae. Adding lists of the salmonids on Australian native freshwater vertebrates other than fish and the and estuarine fauna, together with relevant macroinvertebrate families which occur in overseas work, particularly that done in waters in which salmonids have been New Zealand which shares several native introduced makes quite a catalogue of taxa in common with Australia; Australian fauna which has been exposed to • review research methods and recommend some interaction with these introduced fish. practical methods and priorities for At the outset it must be realised that the research in Australia to clarify the impact greatest impacts would have occurred in the of salmonids on Australian native years immediately following the introduction of freshwater and estuarine fauna; salmonids into Australia. Consequently, the • identify specific localities and native species faunal assemblages in which many of the and populations where the impact of subsequent observations and research projects salmonids is regarded as greatest, and were carried out do not reflect "natural" recommend management options; conditions, but faunal assemblages which are likely to have been substantially modified from those which occurred before salmonids were introduced. Observations that trout do not have an impact because they occur together with various macroinvertebrate and fish species are at best misleading. What the observations reflect is probably a much changed fauna, containing animals which, because of their particular life history characteristics, reproductive strategies or ability to withstand environmental extremes, are able to co-exist with salmonids. Those animals lacking appropriate predator -avoidance mechanisms or whose life history characteristics, behaviour or size make them particularly vulnerable to salmonids are likely to have already been eliminated or restricted to being a much less significant component of the fauna.

1 0 2. SPECIES OF SALMONIDAE IN AUSTRALIA

The family Salmonidae is relatively small, but Detailed early accounts of the introduction of contains some of the world's most popular brown trout are given by Wilson (1879) and angling species. Its members are characterised Nicols (1882); later accounts include those of by an adipose fin, a lateral line, axillary Fraser (1953), Arentz (1966), Lynch (1970), processes on the pelvic fins, small scales and a Gilmour (1973), Clements (1988), O'Brien ( dorsal fin high on the back and further forward 1988), Ritchie (1988) and Walker (1988). than the pelvic fins (McDowall and Tilzey 1980) Self-sustaining brown trout stocks are now . The family is native to the cool and cold widespread in the cooler parts of Australia, waters of the Northern Hemisphere (Berra and isolated populations of sea-run trout 1981). Some species are restricted to fresh occur in Victoria and Tasmania (Kailola et al. water, but others spend various parts of their 1993). Reasons for their success in the lives in the sea. Salmonids have been Australian environment are reviewed by introduced into many countries in the world, Weatherley (1974) and Tilzey (1977). Probable primarily to provide recreational fishing. There key factors in their establishment and success are five species of the family Salmonidae in were the physicochemical and biological Australia (Lake 1971, Merrick and Schmida similarities between many Australian trout 1984, Allen 1989). habitats and those of the ancestral stocks, the minimal competition from native fauna, the abundance and availability of native food 2.1 Brown Trout species and the virtual absence of parasites Salmo trutta Linnaeus and disease (Tilzey 1977). In addition to the existence of self-sustaining Brown trout are native to Europe, from brown trout stocks, releases of hatchery- Iceland and Scandinavia southward to Spain produced trout maintain fisheries in marginal and North Africa and eastward to the Black habitats, in waters lacking suitable spawning and Caspian Seas. They have been introduced conditions or where fishing pressure is thought into many countries and are present on all to be too great for local populations to sustain continents except Antarctica (Frost and Brown (Nicholls 1962, Morrissy 1967, 1972, 1967, MacCrimmon and Marshall 1968, Cadwallader and Tilzey 1980, Cadwallader MacCrimmon et al. 1970). 1983, Baxter 1992, Cadwallader et al. 1992, Roughley (1966) described the introduction and Hall 1992). spread of brown trout in Australia. They were A map outlining the distribution of brown introduced as fertilised eggs brought to trout in Australia is given by Kailola et al. ( Tasmania from the United Kingdom in 1864. 1993). More specific information on the Soon afterwards, stocks in Victoria were occurrence of brown trout in the various developed from eggs obtained from Tasmania, States is given for Tasmania by Fulton (1990), and in 1888 brown trout were introduced into for Victoria by Cadwallader and Backhouse ( New South Wales. Progeny from the resulting 1983) and Tunbridge et al. (1991), for New stocks were distributed widely throughout South Wales by Lake (1957), Llewellyn (1983) Tasmania, Victoria and New South Wales. and Faragher (1986), for South Australia by Brown trout were first introduced into South Morrissy (1967) and Scott et al. (1974), for Australia in 1901, but it was not until the Western Australia by Morrissy (1972), and for 1930s that they became established in Western Queensland by Grant (1978). Australia. Despite repeated attempts, brown trout have not become established in Queensland.

1 1 McDowall and Tilzey (1980), Cadwallader and The brown trout is an excellent angling Backhouse (1983), Merrick and Schmida ( species and is taken primarily on rod-andline 1984) and Kailola et al. (1993) have reviewed using bait, lures or flies. It is considered as the biology of brown trout in Australia. probably the most important introduced sport Brown trout can reach over 1400 mm in fish in Australia (McDowall and Tilzey 1980). length and over 20 kg in weight; in Australia, they have been recorded up to 14 kg in weight and up to 950-1000 mm long. Their optimum 2.2 RainbowTrout temperature range is 4-19 degrees Celsius and they typically occur in cool, well oxygenated Oncorhynchus mykiss waters, usually in streams with a gravel (Walbaum) substrate and moderate to fast flow, but also in cool, clear lakes. Rainbow trout are native to the Pacific Spawning occurs in autumn and winter (April coast of North America, from Alaska to to July), often following a flood. Spawning fish Mexico. Like brown trout, they have been typically migrate upstream into small introduced into many countries and are now tributaries with gravel beds. Pair formation present on all continents except Antarctica ( occurs. The female excavates a depression in MacCrimmon 1971). the stream bed, while the male chases away Roughley (1966) and Clements (1988) have intruders. The male joins the female above the detailed the introduction and spread of rainbow depression and their eggs and milt are released trout in Australia. They were introduced in together, the fertilised eggs settling amongst the 1894 as fertilised eggs brought to New South- gravel. The female then covers the eggs by Wales from New Zealand, where the species had dislodging gravel upstream of the depression, become established after introduction from the and then excavates another. The spawning USA in 1883. Populations soon became area, encompassing several depressions, is established in New South Wales and the called a redd. Brown trout eggs are bright progeny from these stocks were subsequently orange and 4-5 mm in diameter. Development distributed to Victoria, Tasmania and South within the egg takes several weeks, depending Australia. Unlike brown trout, rainbow trout on temperature (about six weeks at 10 degrees appear to have been successfully introduced Celsius). into a few waters in southern Queensland. As Newly-hatched brown trout are 15-25 mm long with brown- trout,- rainbow trout did not become and have a prominent yolk sac. At this stage established in the south-west of Western they are called alevins. They remain in the Australia until the 1930s (Fraser 1953).,, gravel for several weeks, absorbing their yolk, As with brown trout, self-sustaining rainbow before emerging to begin feeding. There is a trout stocks are-now widespread in the cooler general downstream movement after parts of Australia, and releases of hatchery- emergence. The young trout form small shoals produced fish are made in order to maintain in moderately fast water at the tails or margins fisheries in-marginal habitats, in waters lacking of pools. At this stage, they have a series of suitable spawning conditions or where fishing bold, dark blotches along their sides and are pressure is thought to be too . great for local called parr; the blotches are referred to as parr trout populations to sustain. marks. - The reasons for the success of rainbow trout in Although initially gregarious, brown trout Australia are as described for the brown trout. soon become solitary and territorial, A map outlining their distribution in Australia becoming increasingly so as they get bigger. is given by Kailola et al. (1993). More specific They feed on a wide range of animals, information on their occurrence in the various including aquatic insects, crustaceans, States is given in the molluscs and small fish, as well as on references cited for the State distributions of - terrestrial invertebrates which fall on the brown trout. - water surface. McDowall and Tilzey (1980), Cadwallader and Backhouse (1983), Merrick and Schmida (1984) and Kailola et al. (1993) have reviewed the biology of rainbow trout in Australia. Rainbow trout are known to reach 1120 mm They were first introduced to Tasmania in long and more than 18 kg in weight; in 1883, but did not become established. Further Australia, they have been recorded to 9.3 kg. introductions were made from Canada as Their optimum temperature range is 10-22 recently as 1962. Self-sustaining populations degrees Celsius. Essentially, their life history now occur in a few waters, and hatchery and environmental requirements are the same releases maintain populations for recreational as those of brown trout, but they tend to be angling in several other waters (Fulton 1990). more successful in lakes than in rivers and Brook trout have also been released since the streams. Spawning occurs a little later than 1970s in streams on the mountain tablelands that of brown trout, in winter and early spring of New South Wales. However, there are no (August-early November). In other respects, records of the establishment of self-sustaining their breeding biology is similar except that populations, although hatchery releases are their eggs are smaller than those of brown made into several waters for recreational trout and they develop more quickly. angling (Llewellyn 1983, Faragher 1986). Young rainbow trout feed on zooplankton; Attempts to introduce brook trout into South adults feed on a wide range of aquatic Australia in the early 1970s were unsuccessful organisms, including crustaceans, insects, (J. Williams, South Australian Fly Fishers' molluscs and fish, as well as on terrestrial Association - pers. comm.). invertebrates which fall onto the water McDowall and Tilzey (1980), Merrick and surface. Schmida (1984) and Fulton (1990) have The rainbow trout is regarded as an excellent reviewed the biology of brook trout in angling species. It is more easily hooked than Australia. They are known to reach a length of brown trout and a better fighter once hooked. 850 mm and a weight of 6.5 kg; in New South The rainbow trout is the only species of trout Wales they have been recorded to 2 kg, and in cultured commercially for direct human Tasmania to 4 kg. They are a coldwater fish, consumption in Australia, although brown occurring both in streams and cool lakes. trout are produced in hatcheries to provide Brook trout in streams tend to move upstream fish for stocking for recreational fishing into small tributaries. The species does not purposes. Trout farms in New South Wales, usually coexist well with other salmonids, Victoria, Tasmania, South Australia and which could explain why its success in Western Australia mostly produce pan-sized ( Australia is limited. 250-300 g) rainbow trout. In recent years, sea- The breeding biology of the brook trout cage farming of rainbow trout has developed in resembles that of the brown trout, with Tasmania; young trout are reared in spawning occurring in late autumn. Their food freshwater hatcheries until they weigh 70-100 typically consists of aquatic crustaceans, g before they are gradually acclimatised to sea insects, molluscs and small fish, as well as water and transferred to floating sea cages in terrestrial invertebrates. coastal bays for ongrowing (Kailola et at. 1993). The sporting qualities of brook trout are less well known than those of other salmonids. They are said to be readily caught, like 2.3 Brook Trout Salvelinus rainbow trout, but do not fight as well ( fontinalis (Ivlitchill) McDowall and Tilzey 1980). Brook trout are native to north-eastern North America (Scott and Crossman 1973), and have 2.4 Atlantic Salmon Salmo been introduced into many countries throughout the world because of their appeal salar Linnaeus as a sport fish (MacCrimmon and Campbell Atlantic salmon occur naturally in cool and 1969). In Australia, they have a restricted cold waters which flow into the North Atlantic distribution in Tasmania and New South Wales Ocean, from northern Spain through eastern (McDowall and Tilzey 1980, Merrick and Europe to Iceland, Greenland, and along the Schmida 1984). north-east coast of North America (Jones 1959, Scott and Crossman 1973, Mills 1980). In Australia, they have a restricted distribution in Tasmania and New South Wales (Kailola et al. 1993). Atlantic salmon were first introduced to Their diet is similar to that of trout (McDowall Australia as fertilised eggs brought from the and Tilzey 1980, Merrick and Schmida 1984). United Kingdom in 1864. Young salmon were The Atlantic salmon is regarded as a great subsequently released in Tasmania, Victoria sporting fish in its natural range, particularly in and New South Wales with the aim of trying to Europe, where it is often referred to as "the establish sea-runs of Atlantic salmon similar king of fish" (Jones 1959, Mills 1980). Because to those in the United Kingdom. Detailed of its restricted distribution it is of little accounts of these early efforts are given by significance as a sport fish in Australia. However, Boccius (1854), Allport (1864), Johnston (1888) the commercial culture of Atlantic salmon in , Saville-Kent (1888), Wilson (1879), Nicols ( sea-cages in Tasmania has recently become a 1882) and Seager (1888). Although the young major part of the aquaculture industry (Kailola salmon did well in the fresh waters of et al. 1993). Atlantic salmon are also farmed Tasmania, they did not return to these waters, commercially in fish farms in mainland south= after migration to the sea and the attempt to eastern Australia, primarily in New South Wales establish the species was a failure. and Victoria. Atlantic salmon were subsequently reintroduced to Australia as eggs brought to New South Wales from Canada in the 1960s ( 2.5 Chinook Salmon Francois 1965, Arentz 1966, Roughley 1966, Oncorhynchus Clements 1988), and have recently been reintroduced to Tasmania as part of tshawytscha (Walbaum) commercial aquaculture operations (Kailola et The chinook salmon is native to the west al. 1993). coast of North America from southern There are no records of self-sustaining stocks California to Alaska, and north-eastern Asia of Atlantic salmon in New South Wales; from northern Japan to Kamchatka. It has releases of hatchery-produced fish maintain been introduced into several countries, but recreational fisheries in a few impounded only in the South Island of New Zealand have waters in the high country (Llewellyn 1983, self-sustaining populations become Faragher 1986). Atlantic salmon are established (Davidson and Hutchinson 1938, occasionally reported in the lower River Murray Scott and Crossman 1973). in South Australia (B. Pierce, South Chinook salmon were introduced to Australia Australian Research and Development as fertilised eggs brought to Victoria from Institute - pers. comm.); presumably these are California via New Zealand in 1877. Fry from escapees from impoundment stockings in New this consignment were distributed widely in South Wales or from commercial fish farms in Victorian coastal rivers, but did not establish sea- Victoria and New South Wales. In Tasmania, run populations. From 1936 onwards, Atlantic salmon are now established in fertilised eggs were imported on a regular basis hatcheries supplying several sea-cage farms from either New Zealand or the USA and the and have also been released into Great Lake. progeny from these eggs were released into Escapees from sea-cages are present in several several lakes, but only in two deep, crater bays and estuaries in southern Tasmania ( lakes, Lakes Purrumbete and Bullen Merri, did Fulton 1990). flourishing fisheries develop. Subsequently, a Little is known of the natural history of landlocked hatchery stock was developed from Atlantic salmon in Australia. In its natural fish obtained from the USA in the 1960s. This habitat, it is a migratory species, with adults stock is the source of releases into Lakes moving into rivers in winter to spawn. These Purrumbete and Bullen Merri, the only two fish may reach almost 40 kg in weight. Wild waters in Australia in which chinook salmon sea-run populations have not become are currently released (Butcher 1947, Barnham established in Australia, but escapees from 1977, Cadwallader and Backhouse 1983, sea-cages in Tasmania have been caught up to Clements 1988). 10 kg in weight. Atlantic salmon in landlocked populations seldom exceed 2-3 kg (Fulton 1990). Like other trout and salmon, Atlantic salmon require cool or cold waters.

14 Sea-run chinook salmon reach a large size, to 2.6 Summary of Present 1470 mm in length and 57 kg in weight. In Victoria, landlocked chinook salmon have been Status of. Salmon ids in recorded to 890 mm long and 11.4 kg in Australia weight. They thrive in the two deep, cold lakes in which they are stocked and although they Of the five salmonid species introduced into become ripe they do not breed because of a Australia, the brown trout and rainbow trout lack of suitable streams for spawning. They have the widest distributions and have formed feed on a wide range of aquatic animals, self-sustaining populations throughout most of including fish, insects, crustaceans and their ranges. In addition, releases of hatchery- molluscs (Cadwallader and Backhouse 1983). produced fish maintain stocks for recreational fishing purposes in marginal habitats and in waters in which there are no suitable spawning areas. Brook trout have formed self-sustaining populations in a few localities, but there is no evidence that Atlantic salmon or chinook salmon have formed self-sustaining populations; all three of these species have restricted distributions in Australia.

3. REVIEW OF STUDIES ON THE IMPACTS OF SALMONIDS

For ease of presentation, the studies and Whitley (1935) observations on the ecological impacts of Whitley (1935) reported the observation of E. salmonids are considered in the following O. G. Scott, who had made extensive categories: collections of fish in Tasmania, that in • studies which provide distributional Tasmanian streams, as elsewhere, galaxiids information, including observed had been wholly or largely displaced by distributions recorded during fish surveys, introduced salmonids, particularly in the before and after observations, comparisons western districts. of the distributions of particular species in the presence or absence of salmonids, and Williams (1964) statistical analyses of distributional data Williams (1964) reported that brown trout sets for salmonids and native fauna (section were the only fish taken during a survey of 3.1); Lake Tarli Karng, a small, high-altitude lake • studies undertaken during the invasion of in the Gippsland region of Victoria. Galaxias new areas by salmonids (section 3.2); coxii (= G. brevippinis) was not taken either in • experimental introduction studies, e.g. the lake or in the inflowing creek although it introducing salmonids into a delineated had previously been recorded during 1892. stretch of stream and monitoring the Williams remarked that although it was not effects in comparison to a control stretch possible to state definitely that the of stream without salmonids (section 3.3); introduction of trout, which took place over 40 • feeding studies, including analysis of dietary years previously, had led to the extinction of overlap and competition, and predation ( the galaxiid, this seemed a hypothesis for section 3.4); which there was some circumstantial • behavioural studies, including those on evidence. competition for space, either in natural Fish systems or in artificial streams (section 3.5) (1966) ; and Fish (1966) reported substantial changes in • studies on the disease impacts of salmonids the fauna of Lake Waingata, a small, sand (section 3.6). dune lake north of Auckland, New Zealand, following annual releases of rainbow trout fingerlings between 1960 and 1964. Earlier 3.1 Studies on or Relating to releases of trout fry between 1954 and 1959 had not been successful. Up until 1962, " Distributions of Salmonids numbers" of Galaxias gracilis were found in and Native Fauna the lake. The species was scarce in 1963 and could not be found at all during surveys in Gray (1929) 1964 and 1965. Similarly, McDowall et al. ( 1975) reported that the introduction of trout In Popes Creek in southern New South Wales, into Lake Taharoa was also followed by the Grey (1929) reported that Galaxias coxii (= G. virtual extinction of G. gracilis. brevipinnis) was plentiful, and could be found A substantial population of the freshwater in pools practically on the brink of a waterfall, crab Hymenosoma lacustris was found in Lake but that he failed to find any galaxiids in the Waingata during earlier surveys, but none stream below the waterfall. The only other fish were found during the study. Occasional he could find in the area were rainbow trout. specimens of freshwater crayfish Paranephrops planifrons were trawled before 1962, but none were recorded during the study. The population of frogs, which was was surrounded by dense native vegetation of extremely vociferous up to 1962, was scarcely eucalypts and tree ferns. It consisted of a series heard at all during subsequent surveys until of pools separated by long- stretches of shallow the summer of 1965. water. Because of the prevailing dry conditions at the time, water flowin the creek ceased Frankenberg (1966, 1969) during the course of the study. However, this In the headwaters of the Kiewa River on the was thought not to have had a serious impact Bogong High Plains in north-eastern Victoria, on the results because even when the creek Frankenberg (1966, 1969) reported that was running the fish were confined mainly to Galaxias olidus and brown trout displayed an the pools. essentially complementary distribution pattern, The numbers and types of fish in each pool with their ranges overlapping on only one were recorded during December-January occasion. Trout occupied the main body of the 1967-68 (Table 1). Of the pools below the stream, while the galaxiids were usually found rockfall, the one immediately below the rockfall only in situations apparently inaccessible to contained a large number of galaxiids and a trout, such as above waterfalls or in small single trout; some pools contained several tarns adjacent to the main stream. Assuming trout and virtually no galaxiids; other pools that the galaxiids were once continually contained only one or two trout, and galaxiids distributed, Frankenberg concluded that the were relatively more common; and one pool trout appeared to have fragmented their range which contained no trout held several into a number of small isolated populations. galaxiids. All three of the pools above the rockfall contained no trout, and held large Renowden (1968) numbers of G, brevipinnis. Renowden (1968) undertook a survey (primarily Renowden commented that although numbers using a seine net and an electroshocker) of the were small, it certainly appeared that the freshwater fish fauna in the Otway region of introduction of trout into the section of Victoria and found that trout, mainly brown Hendersons Creek below the rockfall had trout, had become established in virtually all brought about a fairly substantial decrease in the streams in the area. He stressed the the size of the galaxiid populations. difficulty in determining exactly what effects the Further, Renowden cited a personal introduction of trout had had on the communication from a local, who reported that indigenous fish fauna because of the lack of it was possible to catch as many as fifty " observations comparing the faunas of waters mountain trout" (i.e. Galaxias truttaceus and before and after the introduction of trout. A Galaxias brevipinnis) in any of the larger pools comparison of the faunas of similar streams, in the river before trout were introduced. At some of which contained trout and some of the time of the study, Renowden reported that which did not, was not possible because of the it was virtually impossible to find these presence of trout in virtually all of the local galaxiids in the main stream of the St Georges streams. However, it was possible to compare a River. section of stream containing trout with another section that did not contain trout. There were several streams in the area in which trout could be found up to, but not above, obstructions such as a waterfall. One such stream, which was also reasonably accessible, was Hendersons Creek, a tributary of the St Georges River. The obstruction on this water was a pile of large boulders which had fallen across the creek, virtually forcing it underground for about 30 m. The creek ran through a succession of steep-walled valleys and for most of its length

18 Table 1. Numbers of fish taken in pools in been made in the past to introduce trout into Hendersons Creek, Otway region, Victoria, during Hartz Lake they did not appear to have the summer of 1967-68. P, pool number; D, survived, and Knott et al. found no evidence of approximate distance upstream (m) from the the presence of trout in the lake. The authors confluence with the St Georges River; T, trout; GM, argue that if trout had become established in Galaxias maculatus; GT, Galaxias truttaceus; GB, the lake it is likely that A. tasmaniae would no Galaxias brevipinnis; E, eels. Pools 1-9 were located longer be a component of the fauna, but that downstream of a rockfall barrier; pools 1012 other species, judging from their occurrence in were located upstream of the barrier. Modified other lakes, would survive. The authors after Renowden (1968). suggest that their findings support the contention of Knott (1973) and Lake and P D GM GT GB E Knott (1973) that trout are responsible for the discontinuities in the distribution of A. 000 1 50 4 4 tasmaniae on the basis of the observed 2 80 400 00 distributions of A. tasmaniae and trout in 3 500 11001 Tasmania. 4 600 111 11 5 680 223 02 Cadwallader (1979) 6 800 6 0 1 07 The distribution of fish within the Seven 7 1100 006 33 Creeks River system, a tributary of the 8 120 1 0 3 02 Goulburn River in the Murray-Darling basin, 0 9 125 1 0034 5 was determined by a survey carried out during 0 10 130 00016 2 the summer of 1975-76 (Cadwallader 1979). 0 11 135 00013 1 Nine native species and five introduced species 0 12 1800 00017 3 were recorded during the survey, but the only evidence of a substantial effect of an Andrews (1976) introduced species on a native species was the During the collection of specimens for a apparent fragmentation of the range of Galaxias taxonomic review of the Galaxiidae in olidus by brown trout, whose numbers in the Tasmania, Andrews (1976) found that system had been augmented until the mid Galaxias brevipinnis was one of the most 1970s by releases of hatchery-reared fish, the widely distributed members of the family. He first release of trout in the system occurring in found that the species was fairly evenly 1886. distributed throughout the central and Galaxias olidus was widespread in the upper coastal regions and in many areas, because of reaches of the system and was recorded at 22 its climbing ability, it was able to invade of the 60 sampling sites, in 1st-order (11 sites), waters which were inaccessible to other 2nd-order (9 sites), 3rd-order (1 site) and 4th- species. However, in many areas its order (1 site) streams. (Stream order is an distribution appeared to have been indication of the hierarchical status of a stream fragmented by introduced salmonids. It was in relation to its tributaries; 1st-order streams found to be abundant in areas which have have no tributaries, 2nd-order streams are never been stocked with trout and also in formed by the confluence of two 1st-order areas which were protected from invasion by streams, 3rd-order streams are formed by the physical barriers, e.g. waterfalls along the confluence of two 2nd-order streams, and so Hugel River were considered to provide a on.) The presence of G. olidus in 3rd-order and barrier which prevented trout from moving 4th-order streams indicates that it is not upstream from Lake St Clair into Shallow confined to the upper limits of catchments. Lake where large shoals of G. brevipinnis Brown trout were recorded at 19 sites, also in occurred. 1st-order (1 site), 2nd-order (4 sites), 3rd-order ( 5 sites) and 4th-order (9 sites) streams. Knott et al. (1978) However, the distribution of trout and galaxiids In a study of Hartz Lake in southern overlapped at only three sites, all of which were Tasmania, Knott et al. (1978) found that the marginal trout habitats. Typically, trout littoral rock fauna was dominated by occupied the main channel and the lower crustaceans, particularly Anaspides reaches of tasmaniae, in contrast to the insect- dominated rock faunas reported for other Tasmanian lakes. Although attempts had

19 highland tributaries, whereas the galaxiids and indicated a highly significant negative were found in the upper reaches of relationship between brown trout and G. tributaries, in situations inaccessible to olidus. trout, such as above waterfalls. In streams in the Otway ranges, brown trout Brown trout spawned in some of the upper were again the most frequently recorded fish, tributaries of the Seven Creeks system, but being taken at eight of the eleven sampling their numbers in the system had been sites, in 3rd, 4th and 5th-order streams. maintained primarily by regular releases of Galaxias brevipinnis was found at the only hatchery-reared fish. Many of these fish were three sites from which brown trout were released into marginal trout habitats from absent, in 3rd and 4th-order streams. Unlike which they disappeared when stocking of the in the upper Yarra River catchment, Jackson waters ended. For example, two of the three and Williams found that brown trout were not sites where galaxiids and trout were recorded abundant (1.2-2.8 individuals per 100 square together during the summer 1975-76 survey metres) in 4th-order streams, and in these were revisited one year later during February streams Galaxias maculatus and Galaxias 1977. At one of these sites the river blackfish truttaceus were abundant (3.9-13.9 individuals Gadopsis marmoratus had also been recorded. per 100 square metres). During the second visit, no trout were On Wilsons Promontory, no trout were recorded, but galaxiids and blackfish were recorded and galaxiids were abundant at all taken in numbers comparable to those taken of the seven sampling sites; G. breuipinnis during 1975-76. At the time of the second occurred at two sites, G. truttaceus at four visit, the streams at each site were reduced to sites and G. maculatus at five sites. a series of small pools (up to 0.5 m deep) with Jackson and Williams concluded that their only a trickle of water in the interconnecting data provided circumstantial evidence that channels. brown trout had deleteriously affected the A few juvenile G. olidus were found in the upper distributions of G. olidus and possibly G. reaches of the main channel after the 1975-76 breuipinnis. survey, but not during the survey (even though the area was extensively fished). This Jackson and Davies (1983) downstream movement of juveniles from an Jackson and Davies (1983) recorded seven upper tributary indicates the mechanism by native and six introduced species of fish at which G. olidus could recolonise the main 115 sampling sites in a survey in the Glenelg, channel in the absence of trout. Wannon and Wimmera River catchments in the Grampians region of Victoria during Jackson and Williams (1980) October-December 1979. They pointed out Jackson and Williams (1980) found eight that the effects of the introduced- species on the species of native fish and two introduced fish native species were unclear, but that during an investigation of the distribution of circumstantial evidence suggested that brown fish in streams in three areas of southern trout had fragmented the range of Galaxias Victoria, viz. the upper part of the Yarra River olidus. catchment, in the Otway Ranges and on Galaxias olidus was the most widespread Wilsons Promontory. Brown trout did not occur native species, occurring at 40 sites in all on Wilsons Promontory,- but did occur in the three catchments, in 1st-order to 5th-order other two areas; this provided an opportunity streams. Brown trout were recorded at ten to compare the distributions of native fish in sites, in 1st-order to 4th-order streams in the areas with and without trout. Wannon and Wimmera River catchments. In the upper Yarra River catchment, brown Typically, both Galaxias olidus and brown trout dominated the fish fauna, being found at trout were recorded at sites with steep 39 of the 49 sampling sites,- in 1st-order to gradients at higher altitudes, and mainly in 6th-order streams. Galaxias olidus occurred at streams flowing through undisturbed only three sites, in a 1st-order, 2nd-order and catchments well shaded by overhanging 3rd-order stream, and was the only native vegetation. species which did not occur with trout. The Galaxias olidus dominated the headwater extent of association of brown trout and some tributaries of all three river systems with the of the native fish in the system was tested exception of those areas where brown trout using a chi-square contingency table

20 occurred. There were many sites on the diversity provided more refuges for galaxiids. In headwater tributaries of the Glenelg River, some stream sections containing trout, containing G. olidus, which appeared suitable galaxiids were found at the edges among debris for brown trout, but the low-lying swampy and overhanging vegetation. At other sites, areas of the Glenelg River probably form an galaxiids were abundant in sluggish effective barrier to invasion by trout, backwaters and trout occurred in flowing particularly in summer when temperatures are water in the main channel. In the smaller high and oxygen levels low. streams, with much less cover, only trout were present. On the other hand, galaxiids were Koehn (1986a) abundant in the Naas River and, especially, Koehn (1986a) recorded nine native and four the Naas Creek where trout were absent. This introduced fish species at seven sites during a catchment was considered to be unsuitable for survey in Badger Creek in the upper Yarra River trout, particularly in summer, because of its catchment in southern Victoria between May low discharge and abundant aquatic 1984 and March 1985. Brown trout were taken vegetation which choked the channel. at four sites, being most abundant at the two most upstream sites. Galaxias olidus was Lintermans and Rutzou (1990) recorded at two sites in the middle and lower Lintermans and Rutzou (1990) recorded two reaches of the creek, where numbers of brown native species (Galaxias olidus and the two- trout were low, but was absent from the two spined blackfish Gadopsis bispinosis) and uppermost stream sites (where habitat rainbow trout in surveys carried out at 28 conditions appeared suitable) where brown sampling sites in the upper Cotter River trout numbers were high. One specimen of catchment in the Australian Capital Territory Galaxias truttaceus and three specimens of during 1988 and 1989. The rainbow trout was Galaxias brevipinnis were also taken during the the most widely distributed species, being survey. The absence of G. olidus and the small recorded at 20 sites, in 2nd to 5thorder numbers of G. brevipinnis in the upper reaches streams, whereas G. olidus had the most of the system, where they would normally be restricted distribution, being recorded at only expected to be more abundant, led Koehn to six sites, usually in the smaller, headwater, 1st suggest that their numbers may have been to 3rd-order streams. affected by the presence of trout. Galaxiids occurred with trout at only one site, where a single individual of each species was Jones et al. (1990) recorded above a 2.5 m waterfall, while below Jones et al. (1990) recorded Galaxias olidus the waterfall numerous trout and no galaxiids and introduced brown trout and rainbow trout were found. An inspection of the site about one in a survey carried out at 22 sampling sites in year previously had indicated that only the Naas-Gudgenby River catchment in the galaxiids were present above the waterfall. In Australian Capital Territory during summer the period between the initial inspection and 1986-87. The galaxiids had a widespread but the survey it is thought that a period of high fragmented distribution, occurring at 17 of the flow enabled trout to move upstream above 22 sites, in 2nd to 6thorder streams, and were the waterfall. Four of the six sites where most abundant in the smaller headwater galaxiids were recorded were above waterfalls streams and minor tributaries. Brown trout or barriers to trout access. It is unknown occurred at eight sites, principally in the main whether barriers exist below the other two river channels, in 4th to 6th-order streams. sites. The authors considered that the Rainbow trout were more widely distributed fragmented distribution of G. olidus and its than brown trout, extending further upstream absence from sites occupied by rainbow trout into the smaller tributaries, and were found at provides evidence of the adverse impact of eleven sites, in 3rd to 6th-order streams. trout on this species. The authors found an inverse relationship between trout biomass and galaxiid biomass. Minns (1990) They considered that at those higher-order Using the New Zealand Freshwater Fish stream sites where both trout and galaxiids Survey data base which contained almost 6, occurred together, the increase in habitat 500 entries by November 1985, Minns ( 1990) analysed presence-absence data for the New Zealand freshwater fish fauna for evidence of species interactions and of links reported to have resulted in the galaxiids with land use and geological patterns. Native being almost completely eliminated from a and introduced species had overlapping major part of their former range in this stream geographical distributions but tended to be within three years. Earlier, Fulton (1978) had segregated at the site level. The number of pointed out that the downstream limit of the freshwater fish species found in catchments G. fontanus population in the Swan River and lakes increased with catchment and lake coincided with a natural barrier to trout area respectively. Species-area curves were invasion, and postulated that the trout were developed for lotic and lentic sites and responsible for the absence of galaxiids explained a small portion of the variation. further downstream. Regressions involving land use and geological Populations of Galaxias johnstoni were variables accounted for more variation. restricted to isolated sections of the Clarence Analysis of co-occurrence patterns, where River system, the species being absent from all distributions overlapped, indicated relatively sections of the system where brown trout were more negative associations between native and established, including the type locality of G. introduced species than amongst native fish johnstoni. Natural barriers limited the themselves or amongst introduced fish upstream invasion of brown trout. For themselves. The presence-absence patterns of example, in the Clarence River system below several native species were related to land use Clarence Lagoon there was a steep cascading and geological factors. Minns concluded that stretch of stream which prevented upstream both changes in land use and introduced fish, invasion by trout. Brown trout were the only particularly brown trout and rainbow trout, fish present below the cascade, but had caused changes in the distribution of immediately above the cascade, and even in native fish species. some of the pools within the cascade, G. johnstoni and brook trout occurred. Sanger and Fulton (1991) . Interestingly, G. johnstoni and brook trout were In a paper on the conservation of endangered also found together in Clarence Lagoon. Brook freshwater fish in Tasmania, Sanger and trout were reported to be unable to coexist Fulton (1991) summarised information which with brown trout in Tasmanian rivers and suggests an impact of introduced trout on lakes. Galaxias fontanus, Galaxias johnstoni and Populations of Galaxias tanycephalus were Galaxias tanycephalus. restricted to two lakes, viz. Arthurs and Woods Populations of G. fontanus occurred in small Lakes, and a few associated streams. Sanger tributaries of the Macquarie River and in the and Fulton reported that predation by brown Swan River above Hardings Falls. Other trout was recognised as a major source of streams in the area which contained no mortality in the Woods Lake population, wholly freshwater fish (some contained eels) although the galaxiids appeared to be "coping were very small and dried up in summer. Most adequately with this pressure". However, the of the permanent streams in the area galaxiid population in Arthurs Lake was much contained self-sustaining populations of smaller than in Woods Lake and it was brown trout. The streams containing G. suspected that predation by brown trout was fontanus all had self-sustaining populations of at least partly responsible for this, although trout downstream of the galaxiid populations. the authors reported that the two species have All the G. fontanus populations were coexisted for about 100 years. considered to be under threat from brown trout. Their continued existence was thought Sloane and French (1991) to be dependent on natural barriers preventing Sloane and French (1991) reported that the brown trout moving upstream. These barriers relationship between observed galaxiid ranged from shallow marshes to substantial abundance and trout population density in the waterfalls. Predation on G. fontanus by trout western lakes of the central plateau of was reported to have been observed following Tasmania was not clear. Conceding that , penetration of the less substantial barriers by neither parameter could be readily measured small numbers of trout. A recent introduction in these remote waters, their observations of brown trout above Hardings Falls on the suggested that in some lakes (e.g. Lake Ingrid) Swan River was both trout and galaxiids were

22 particularly abundant, whereas in other waters availability of background data with the (e.g. Lake Malbena) the abundance of both intention of producing a balanced study introduced and native fish seemed to be quite design. Each land use type was represented by low. In lakes where trout were absent or in low two catchments and, within each catchment, numbers, galaxiids were observed to be more the main channel and at least three tributaries conspicuous in the open surface waters. When were selected. At the individual site level, three trout were abundant, the galaxiids appeared to pool/riffle sequences within each stream be more confined to the lake margins, the channel were selected, incorporating as much rocky shorelines and the shallow bays of the stream as possible, so that the top site dominated by emergent reeds. was located near the headwaters and the bottom site was near the confluence with the Shirley (1991) main channel. Following a study of the distribution and Catchment-level variables, e.g. altitude and ecology of the endangered Galaxias fuscus in gradient, were derived from existing maps. the Goulburn River system in central Victoria, Stream channel characteristics, e.g. physical Shirley (1991) concluded that trout (brown features such as waterfalls and surrounding and rainbow trout) were influencing the vegetation, were recorded, as were in-stream distribution of the galaxiid. Analysis of the physical variables, such as velocity and species composition at sites in areas where G. substrate type, and chemical characteristics. fuscus had previously been found indicated a Statistical analyses were performed in two negative effect of the presence of trout. stages. Firstly, each sampling site was placed Of the 14 sites where G. fuscus had previously in two different classifications, one based on been recorded, it was still the only species land use, the other based on the presence of G. present at seven of the sites, trout were the vulgaris and trout. The fish classification only species present at four of the sites, and at included sites with no fish, sites with G. the remaining three sites (all within a 350 m vulgaris only, sites with trout only, and sites stretch of the Taggerty River) both rainbow with both G. vulgaris and trout. For each trout and G. fuscus were present, but the classification (land use and fish) separate density of galaxiids (number of fish per square multiple discriminant function analyses were metre) was depressed compared to sites in performed on all variables to determine which trout-free areas. were important in discriminating amongst the The extant populations of G. fuscus in the classes. Comparison of the variables included upper reaches of the Keppel Hut Creek in the two models permitted Townsend and catchment were found to be separated from Crowl to determine whether or not land use rainbow trout by a single large cascade, the could account for the observed fish trout having successfully circumvented several distributions. Secondly, multiple regression smaller cascades lower down stream. analyses were used to determine which variables best explained the observed densities Townsend and Crowl (1991) of G. vulgaris. Townsend and Crowl (1991) conducted an Of the 198 sites surveyed, 54 contained no electrofishing survey of the fish at 198 sites in fish, 69 had brown trout only, 63 had G. eight catchments in the Taieri River basin of vulgaris only, and 9 had both brown trout and the South Island of New Zealand and found a G. vulgaris. The most important variables in strong negative association between the discriminating fish species assemblage classes distribution of introduced brown trout and were the number of waterfalls with a height of Galaxias vulgaris, a native freshwater fish 3 m downstream of the site, the proportion of similar in many respects to Galaxias olidus cobble in the substrate, and the elevation of which occurs in Australia (McDowall 1980, the site. 1990a). Although habitat degradation as a result of The survey included tributary catchments agricultural and forestry practices was encompassing homogeneous examples of the associated with lower densities of fish, these four major land uses of the region, viz. native reductions were found in all fish species and bush, native tussock grassland, plantations of did not help to explain the trout/galaxiid introduced pines and agricultural pasture. pattern. The statistical analyses incorporating Catchments were chosen according to the the various physical, chemical and biological variables indicated that streams had also been invaded by Galaxias presence and abundance of galaxiids were best brevipinnis, another potential competitor and predicted by the absence of trout. In most predator. cases, G. vulgaris was found only above waterfalls which were large enough to prevent Ault and White (1994) the upstream invasion of trout. Ault and White (1994) examined the effect of In support of their conclusion that brown brown trout on Galaxias truttaceus in several trout were responsible for a negative effect on streams in south-eastern Tasmania by using galaxiid abundance and distribution, population abundance models to compare Townsend and Crowl cited historical records habitat use by the galaxiids in streams with which suggested that G. vulgaris was once and without trout. The study sites included 35 widespread in the Taieri River basin. Trout sites in five streams lacking trout and 14 sites were introduced in the 1870s and their in four streams' containing trout. Habitat use by distribution and abundance gradually G. truttaceus was investigated with respect to increased. Although there were no quantitative four principal components extracted from eight historical records concerning G. vulgaris, it was habitat variables, viz. mean depth (1), mean clear that its distribution and abundance had water velocity (2), mean substrate size' (3) and decreased throughout the catchment. Four of proportions of detritus (4), vegetation (5), silt the eight study catchments were in native and algae (6), overhead cover (7) and instream tussock and bush habitats and had received cover (8). Fish were sampled by electrofishing. minimal human disturbance, so that historical Different size-classes of G. truttaceus displayed galaxiid distributions might be expected to varying non-random patterns of . habitat use, have remained intact if land degradation was shifting from shallow, open sections of stream the responsible factor. However, these sites to deep sections with plenty of cover as they showed the same scale of population increased in size. All size-classes preferred slow- fragmentation as the most heavily modified flowing sections of stream to fast-flowing catchments, consistent with the hypothesis sections. Population abundance models were that brown trout and not land use determined constructed for three size-classes of G. the observed distribution of G. vulgaris. truttaceus, viz. less than 85 mm long, 85-125 mm long and longer than 125 mm. Given the Hamr (1992) hydrologically variable nature of the study Galaxias pedderensis and Galaxias parvus streams, all the models were found to be occurred in the original Lake Pedder and its reasonably successful in explaining the feeder streams. In 1972, a new enlarged Lake observed variation. The application of the Pedder was created as the result of the models to streams containing brown trout construction of a large hydroelectric scheme. indicated that the presence of trout was more Following the creation of the new lake, there important than habitat characteristics in was a large population explosion of galaxiids, determining the abundance of G. truttaceus. In with large schools being observed until the late streams containing trout, the density of each 1970s. In the early 1980s, the number of size-class of galaxiids was substantially less galaxiids in the lake declined dramatically. than that expected on the basis of habitat Surveys indicated that although numbers of G. characteristics alone. parvus remained high in the Pedder region, the The authors concluded that their study number of G. pedderensis had undergone a provides evidence that brown trout adversely dramatic decline in the lake and its affect G. truttaceus because differences due to surrounding streams. The species was found habitat characteristics were accounted for to be absent from the lake and occurred in low when streams with and without trout were numbers in only two feeder streams. The compared. causes of the demise of G. pedderensis were not clear, but it was considered that the McIntosh et a/. (1994) introduction of brown trout may have been at McIntosh et al. (1994) investigated the impact least partly responsible. However, the situation of small (less-than 100 mm long) and large ( was complicated because the lake and more than 100 mm long) brown trout on the adjoining distribution of Galaxias vulgaris (very similar

24 in many respects to Galaxias olidus) in the Davies (1989) reported that he had found a Shag River in the South Island of New negative correlation between the abundance Zealand. They described the macrohabitat in of non-trout fish species and the abundance riffles in the river in terms of substrate type, of brown trout in Tasmanian streams. He flow, elevation, and vegetation characteristics. pointed out that although the impact of the Fish were sampled by electrofishing. introduction of trout on the Tasmanian native Galaxiid densities were lower in riffles fish fauna is unclear, the high proportion of containing large trout than in riffles with only brown trout in the total fish standing-stock small trout or no trout. Trout size was found of streams would suggest some considerable to be the most important variable determining impact. galaxiid density. Densities of galaxiids less Comments and observations on the effects of than 80 mm long were reduced in the presence introduced salmonids on the distribution and of large trout, whereas densities of galaxiids abundance of New Zealand taxa are greater than 80 mm long were not affected. summarised and reviewed by Thomson (1922), Riffles with large, small or no trout varied in Phillipps (1940), Allen (1949, 1961), Waugh ( water depth, substrate type and elevation, but 1973), McDowall (1968, 1976, 1984, 1987, the authors thought that these differences were 1990a, b, c), Glova (1989), Crowl et al. (1992) unlikely to account for variations in galaxiid and Townsend (in press). densities because selection for these particular habitat features accounted for only a small proportion of the observed variation in galaxiid 3.2 Studies Undertaken During density. The authors suggested that a change in the Invasion of New Areas macrohabitat use by galaxiids from fast by Salmon ids current velocities at sites without trout to slower velocities at sites with large trout may Tilzey (1976) be explained by competition for areas of high Tilzey (1976) sampled the fish fauna of all the velocity, which potentially were the better major streams within the Lake Eucumbene feeding areas. However, a combination of catchment in south-eastern New South Wales interspecific competition and predation by by electrofishing and poisoning with rotenone large trout was considered the most likely during 1971. Galaxias brevipinnis was found in cause of the observed reductions in the only four streams and Galaxias olidus was density of smaller galaxiids. found in only one (Four Mile Creek) of the 27 Other Observations and Comments streams sampled, whereas introduced In a study of the fish fauna of streams in the salmonids (brown trout, rainbow trout or both) Western Port catchment, Koehn (1986b) noted occurred in all but the stream containing G. that the absence of Galaxias maculatus from olidus. deep pools in Cardinia Creek may be Fish biomasses in streams in the Lake attributable to the presence of large brown Eucumbene catchment varied considerably, trout and rainbow trout; G. maculatus was with biomasses in streams flowing through abundant in the creek immediately below forest being usually significantly lower than these pools where trout were not present. those in streams flowing through grassland. Furthermore, in an investigation of the Nevertheless, the biomass of G. brevipinnis in distribution of freshwater fish in the Otway the four streams in which trout also occurred region of south-western Victoria, Koehn and O' was markedly lower (0.01-0.30 grams per Connor (1990) suggested that the distribution square metre of substrate) than that in Four of Galaxias brevipinnis may be affected by the Mile Creek which contained only G. olidus (8.08 presence of brown trout which at some grams per square metre). However, as Tilzey sampling sites appeared to restrict the pointed out, total fish biomasses (i.e. the galaxiids to shallow riffles which were not biomasses of trout and galaxiids combined) in accessible to trout. these four streams were lower (0.94-6.10 grams per square metre) than 8.08 grams per square metre and the galaxiid species were different, so comparisons should be made with caution. The streams containing G, brevipinnis all had Comparison of the stomach contents of some steep gradients, with consequent rapid flows, of the rainbow trout and G. olidus taken from and ran through forest before directly entering Four Mile Creek on the sampling day in 1974 Lake Eucumbene. These streams were used indicated that the species composition of the annually by lake-dwelling trout for spawning. diets of the trout and galaxiids were essentially Four Mile Creek, containing G. olidus, was similar. often inaccessible to trout because of a 3 m Tilzey reviewed historical data for the area high waterfall which and, although early records on the distribution became exposed when the lake level fell below of galaxiids were lacking, thought it was likely 1155 m above sea level. that galaxiids once occurred throughout the Subsequent sampling of Four Mile Creek in entire Lake Eucumbene catchment. Assuming 1974 indicated that rainbow trout had that widespread populations or a series of invaded the stream below the 3 m high contiguous populations of G. breuipinnis and waterfall since 1971. G. olidus existed previously, Tilzey concluded In 1971, G. olidus was abundant both above that the introduction and subsequent success and below the waterfall, with biomasses of 8. of trout were primarily responsible for the 42 and 7.84 grams per square metre present much fragmented galaxiid distribution. respectively. In 1974, no galaxiids were found below the waterfall in the same 0.5 km stretch Raadik (1993) of stream which was electrofished in 1971. In the Goulburn River catchment in central Rainbow trout were found to have invaded this Victoria, Raadik (1993) reported that trout, water and no other fish species were present; particularly rainbow trout, had expanded their 25 trout with a biomass of 3346.3 g were range into nearly all the extant G. fuscus taken from a 115 m stretch of stream, with populations, and were continuing to colonise two trout about 420 mm long making up 64. further upstream-with a consequent 4% of the total biomass. Galaxiids were still contraction in the range of the galaxiids. present above the waterfall, their biomass (10. In waters such as the Taggerty River and 16 grams per square metre) being greater than Pheasant Creek, where there were no physical that recorded in 1971. These observations barriers to:prevent the invasion of trout, the suggested that the presence of rainbow trout range of G. fuscus was contracting rapidly. For was responsible for the disappearance of example, in June 1991, rainbow trout were galaxiids below the waterfall. first reported to have moved into a stretch of Comparisons of the length frequency Pheasant Creek occupied by G. fuscus; seven distributions of the G. olidus population in trout were collected and removed from a 500 Four Mile Creek in 1971 and 1974 indicated m section of the creek and 86 adult G. fuscus that there had been little change in the were recorded. Six months later, in December, population structure, so the disappearance of 31 rainbow trout were removed from the same G. olidus below the waterfall could not be section of creek and only 55 adult G. fuscus attributable to a change in population were recorded, a reduction of 36% in adult structure. numbers in six months. Four year-classes (1970-73) of brown trout Furthermore, the stomachs of rainbow trout were found below the waterfall. Comparison of taken from Pheasant Creek and Taggerty River their mean, back-calculated growth rates contained G. fuscus. One trout (167 mm long) indicated that growth of the 1970 year-class out of seven taken from Pheasant Creek was markedly higher than that of succeeding contained three galaxiids in its stomach and year-classes, and exceeded that of the 1970 one in its mouth; the length range of the year-class of rainbow trout in Lake galaxiids was 40-60 mm. Three trout out of 16 Eucumbene and that of brown trout in a taken from the Taggerty River contained G. stream at a similar altitude and flowing fuscus. through essentially similar terrain. Raadik concluded that trout predation on G. Furthermore, comparison of the growth fuscus was a major threat to the survival of curves of the 1970 year-classes from Four the galaxiid. Mile Creek and Lake Eucumbene indicated that the Four Mile Creek trout had not resided in lentic waters.

26 Class and Lake (in prep) conditions, which resulted in the drying up of Closs and Lake (in prep) mapped the most of the pools along the river, they longitudinal distribution of brown trout and suggested that trout could only have survived Galaxias olidus in the upper reaches of the in the deeper permanent pools further intermittent Lerderderg River in central downstream. The elimination of trout from the Victoria over four summers between 1985 upper reaches of the system during the and 1988. During this period, the drought would have created trout-free habitat distribution of the trout extended upstream for G. olidus to colonise. If trout had occupied and, coincident with this upstream expansion the main channel of the river before the 1982- of the range of brown trout, there was a 83 drought, it is likely that G. olidus survived contraction in the distribution of G. olidus. within the catchment in the uppermost At the start of the study in the summer of reaches of headwater streams. 1985, brown trout occupied only a short section of stream at the downstream end of the study area. The distribution of trout and 3.3 Experimental Introduction galaxiids overlapped for a short distance. Study Neither species was particularly abundant, suggesting that the populations of both species Fletcher (1979) were recovering from the effects of the 1982-83 Before selecting a stream in which to make an drought. Many pools throughout the upper experimental introduction of brown trout, reaches contained no fish. Fletcher (1979) chose four streams in Victoria The distribution of brown trout expanded which contained parapatric populations of about 1-1.5 km upstream each year between trout and Galaxias olidus separated by a 1985 and 1988; the distribution of G. olidus waterfall for preliminary investigation. These correspondingly contracted upstream. The sites included two lowland streams: Watchbox distribution of each species continued to Creek and Running Creek, and two alpine overlap for a short distance during each streams: a tributary of Cope Creek on the summer of the survey, although the zone of Bogong High Plains and a tributary of Buffalo overlap moved progressively upstream. In Creek on Mt Buffalo. In both alpine streams, G. contrast to the situation at the start of the olidus was the only fish species present above study in the summer of 1985, virtually all of the waterfall and brown trout were the only the pools in the survey area contained either fish present below the waterfall. In Running trout or galaxiids, suggesting that the total Creek, G. olidus and Gadopsis marmoratus abundance (irrespective of species) had occurred above the waterfall and had a total increased. By the time the river pooled in the mean biomass of 8.82 grams per square metre. summer of 1988, the distribution of G. olidus Below the waterfall, G. olidus, G. marmoratus and had contracted into very small headwater eels were present, but the dominant species streams and had fragmented into two sub- was the brown trout which accounted for 70% populations. Between 1987 and 1988, brown of the total mean biomass of 5.87 grams per trout had succeeded in moving upstream square metre. above a 1 m high waterfall. In Watchbox Creek, G. olidus was the only fish In the summer of 1988, an extended period of species present above the waterfall and had a dry weather resulted in high levels of mortality mean biomass of 1.92 grams per square metre. in trout at the upper limit of their range, A few G. olidus were present below the suggesting that their upstream limit could waterfall, but the dominant fish species in this ultimately be restrained by their inability to stretch of stream was the brown trout, with a tolerate prolonged periods of low stream flow mean biomass of 3.23 grams per square and high temperatures which occurred in the metre. The galaxiids at the sites below the headwaters of the Lerderderg River. waterfall had a mean biomass of 0.19 grams The authors cited references which indicated per square metre. that brown trout were abundant in the upper Fletcher compared the diets of the fish in the reaches of the Lerderderg River before the four streams on a seasonal basis and found 1982-83 drought. Under the severe drought that there was positive (often statistically significant) overlap in the diets of G. olidus and brown trout. The major items of overlap were terrestrial dipterans and hymenopterans. allow for a mortality of 60-90% which would The diets of juvenile galaxiids and juvenile yield a biomass at the end of the experiment of trout also positively overlapped. Their diets 1-4 grams per square metre, similar to that for consisted primarily of chironomids, which were trout in the main channel below the waterfall. relatively less abundant in the benthos than in The practical difficulties of such work soon the diet, and were highly selected. became apparent. A flash flood, which raised Ephemeropterans (mainly Atalaphlebioides) the water level above the barriers at the were eaten by both fish species, but they were boundaries of the experimental and control relatively abundant in the benthos during all sections, caused trout to be lost from the seasons so were not necessarily highly experimental section. No trout were found to selected. There was also a positive overlap in have moved upstream into the control section. the diets of brown trout and G. marmoratus, A second stocking of trout was made on 9 with the range of items taken by both species December to bring the biomass of trout in the including similar benthic taxa, particularly experimental section to 9.6 grams per square Atalaphlebioides; chironomids were also taken metre. by juveniles of both species. The experimental and control sections were A site above the waterfall on Watchbox Creek electrofished in the following April, four months was chosen for the introduction experiment. after the final introduction of trout. None of the Barriers were constructed in shallow areas at large trout survived, probably because of the each end of the 70 m long experimental high ,summer water temperatures and shallow section. The barriers consisted of wire mesh water. The mortality (= disappearance from the supported by metal stakes, with nylon fishing experimental section) of the two batches of net (10 mm aperture) attached to prevent fish young-of-the-year trout was 86.7% and 80%, moving through the barrier. The 70 m long similar to that reported in previous studies of control section was located immediately hatchery-reared trout. upstream of the upper barrier. The mean width The establishment of the trout in the of each section was 1.5 m, and their area experimental section appeared to be at the approximately 105 square metres. Both expense of the galaxiids. Both the number sections were similar physically and consisted and biomass of G. olidus were lower in the of a series of pools (to 1 m deep) and flat areas. experimental section than in the control. Each section was marked out into ten 7 m section. long zones to facilitate recording fish At the end of the experiment, one galaxiid was observations and siting of invertebrate found in the stomach of a trout in the samples. The experiment was conducted during experimental section, and two galaxiids formed summer to include the anticipated peak the entire stomach contents of a trout taken in feeding and activity periods of the fish, at a the control section; this trout was thought to time when it was thought that low rainfall and have entered this section during a flash flood consequent streamflow minima would reduce which occurred two days before the end of the the possibility of the barriers being washed experiment. away. The duration of the experiment was to Analysis of the length frequency distributions of be four months. Samples of the benthic the galaxiids in the experimental and control invertebrate fauna in each section were taken sections -indicated that the number of galaxiids before the trout were introduced and each greater than 60 mm in length was similar in month throughout the experiment. the two sections, but the number of young-of- Estimates of the numbers and biomass of the-year galaxiids was significantly lower in the galaxiids in the experimental and control experimental section compared with the sections were similar before the start of the control section. This suggested that there may experiment. have been size-selective predation by the trout The trout, including 30 young-of-the-year on the 0+ galaxiids. fish (47-60 mm long) and six fish about 18 The condition factors of the galaxiids, months old (140-185 mm long), were particularly the larger individuals, in the stocked in the experimental section on 11 experimental section were significantly less November. The biomass of the introduced than those of the galaxiids in the control trout was 10.1 grams per square metre to

28 section. Young galaxiids (0+ and 1+ age- trichopterans and molluscs. Considerably classes) fed mainly on ephemeropterans and greater diversity exists in lakes. Small fish are trichopterans; older galaxiids (2+ and 3+ age- eaten mainly by the larger salmonids, the classes) took more terrestrial items. The diet of particular species taken depending on the local brown trout showed positive correlations with fauna. Those native species which are most the diets of all age-classes of G. olidus, and likely to be affected are those whose habits these correlations were significant in almost all and appearance make them attractive to cases. Ephemeropterans, trichopterans and salmonids (Allen 1961). terrestrial items were the main items of As pointed out by Tilzey (1977), trout are overlap. Trichopterans formed the bulk of the opportunistic predators and usually select the diet of the trout, constituting 49% by volume, largest and most readily accessible prey. In this with Ecnomus, Aphilorheithrus and a tasimid context, the remarks made by James Youl ( being the major taxa consumed; all had high who was involved in the first successful electivity indices, indicating that they were introduction of brown trout and Atlantic highly selected. In the control section, tasimids salmon into Australia) in a letter to New formed 19.6% of the volume of the diet of Zealand are very interesting "... I beg you on galaxiids 70-90 mm long, whereas in the no account to permit the brown trout to be experimental section, where the trout introduced... until you have got the salmon consumed tasimids, these trichopterans were fairly established... They are the greatest not eaten by galaxiids. These results imply that enemies the salmon can have. I can compare competition for food may have occurred, them to nothing, but wolves in a flock of contributing to the poor condition of the sheep. Again and again I have warned Dr galaxiids in the experimental section. Officer, of Tasmania, of the danger of admitting Some invertebrates were less dense in the these voracious fish into any stream suitable benthos in the experimental section than in for salmon before the salmon are established the control section, but others were found to therein..." (Thomson 1922). be more abundant. The densities of most of Given the large size to which trout and salmon the benthic invertebrates did not vary between can grow compared to most of the native the two sections, indicating that in the short aquatic fauna of Australia, it is likely that the term they were not affected by the change in main impact of salmonids has been via predator pressure. predation rather than competition (Tilzey 1977) . However, competition for food and space between salmonids, particularly juveniles, and 3.4 Feeding Studies, I the larger, aquatic, native predators (mainly fish and the larger macroinvertebrates) is also ncluding Analysis of likely to occur. This interspecific competition Dietary Overlap and may involve either interference competition or exploitation competition. Interference Competition, and competition occurs when one species establishes a territory and physically excludes Predation other species: exploitation competition occurs Introductory Comments when both species use a resource which is in short supply (Fletcher 1986). It is extremely Since it is almost axiomatic that game fish difficult under field conditions to demonstrate should be carnivorous, it follows that one of that a particular food item is in short supply the principal impacts of salmonids on the and, therefore, to demonstrate that competition native freshwater fauna will be their for food is occurring. predation on small native animals, both From the point of view of providing evidence vertebrate and invertebrate. The extent to of an impact of salmonids on the native fauna, which the various food items are eaten there are no quantitative or even qualitative depends on their abundance and on the data bases on the composition of aquatic extent to which their habits and structure communities before the introduction of make them available to and eatable by the salmonids into Australia and no accounts of salmonids. Amongst invertebrates, the main the effects of the first introductions of groups eaten by stream-dwelling salmonids salmonids on the composition of aquatic are chironomids, ephemeropterans, communities. Most studies on the feeding Other studies on the food and feeding relationships between salmonids and the relationships of salmonids in Australia, native fauna were undertaken long after although not necessarily providing evidence of salmonids had become established in an impact, nevertheless provide insights into Australia. the mechanisms whereby impacts can occur In relation to the effects of salmonid predation or into the reasons why some native aquatic on aquatic communities, including the effects animals are more susceptible than others to on native predators which may consume the predation or -competition from salmonids. same foods, the most substantive evidence of These studies, together with relevant New impacts comes from records of the events Zealand studies on the same or closely-related occurring during invasions of new areas by native taxa, are reviewed in the following salmonids (e.g. Tilzey 1976, Sanger and Fulton sections. 1991, Raadik 1993), of the composition of the invertebrate faunas in waters containing Morrissy (1967) parapatric populations of salmonids and native Morrissy (1967) studied the food of brown fish (e.g. Fletcher 1979) and of the effects of trout and rainbow trout in several waters near experimentally introducing trout into a new Adelaide in South Australia. He found that area (e.g. Fletcher 1979) (see sections 3.2 and there was an unusual absence of 3.3). representatives of the larger native aquatic Although not providing evidence of an adverse fauna in Sixth Creek, a tributary of the Torrens impact, i.e. that trout are the cause of the River, compared with other waters and demise of a particular species, several studies postulated that this was brought about by the and observations on the food of trout in trout selectively eliminating, or reducing to Australia, e.g. McKeown (1934a, b, c, 1936, very low numbers, species which were large 1937, 1955), Evans (1942). Butcher (1945, and/or highly accessible to them. He suggested 1946), Jenkins (1952), Lake (1957), Williams ( that the total biomass of aquatic animals had 1965), Wilson (1966), Knott (1973), not been reduced, but that there had been a Frankenberg (1974), Bishop and Tilzey (1978), change in the relative abundance of the Cadwallader (1979), Faragher et al. (1979), various species, and that such changes in Faragher (1980, 1983), Pidgeon (1981), aquatic community structure seemed to be a Humphries (1989), Lintermans (1991,1992) consequence of the introduction of trout to and Sloane and French (1991) provide an waters which had not previously been inventory of the types of fauna eaten by subjected to such large predators. Trout were salmonids, and indicate that the diets of abundant in Sixth Creek and had a continuous introduced salmonids and native fish often distribution throughout a wide range of habitat overlap. types, whereas in the other waters investigated In some cases, these observations indicate the they occurred in lower numbers and exhibited potential for trout to cause the demise of a discontinuous distributions. particular species. For example, the One of the missing groups in Sixth Creek was observation reported by Humphries (1989) the Galaxiidae. Morrissy reported local farmers that Galaxias auratus in a Tasmanian alpine recalling "enormous numbers" of these fish lake represented 99% of the number of food before the, 1940s, when the trout started organisms in the stomachs of the 29 brown dispersing up the creek from the Torrens River, trout examined, suggests that predation by and attributed their elimination to the trout could have a severe impact on the presence of trout. Galaxias kayi (= G. olidus) galaxiids in this particular lake. Further, can still be found in the small tributaries of Lintermans' (1992) observation of predation by most streams where they can survive rainbow trout on the highland water skink stagnation and drought during summer, Eulamprus tympanum and Gillespie's (1995) conditions which trout cannot tolerate. Other observations of predation by brown trout on animals which appeared to be highly the tadpoles of several frog species indicate the vulnerable to predation by trout and which potential for salmonids to have an impact on were absent from Sixth Creek were tadpoles, aquatic vertebrates other than fish. yabbies Cherax destructor, whirligig beetles of the family Gyrinidae which were numerous on the surface of pools in which

30 there were no trout, and large water beetles of the various food categories in their diets. the family Dytiscidae which were observed in a Kendall rank correlations indicated that the tributary of Sixth Creek. diets of the two species were similar on all The larger animals which can still be found in but one occasion. Because of apparent Sixth Creek, e.g. the predatory dragonfly differences in habitat preferences, the nymphs (Aeschnidae, Corduliidae and similarity in diets was considered as having Gomphidae), apparently manage to persist the potential to give rise to indirect because for part of their life cycle they remain competition. inaccessible to trout under stones in shallow riffles and in algal beds. However, they are Cadwallader and Eden (1981, 1982) vulnerable when they drift and move in open, The food and growth of one-year-old, hatchery- relatively quiet water when they are small and produced, chinook salmon released into Lake also when they emerge from the water. Purrumbete, Victoria, were investigated over a two-year period (1976-78) by Cadwallader and Cadwallader (1975a) Eden (1981). Fish formed the bulk of the Cadwallader (1975a) studied the seasonal stomach contents of the salmon for most of the feeding relationships of brown trout and time, except in spring. Galaxias maculatus was Galaxias vulgaris (similar in many respects to usually the only fish species taken, but Galaxias olidus), bullies Gobiomorphus Galaxias truttaceus and pygmy perch breviceps (family Eleotridae) and eels Anguilla Nannoperca australis were taken occasionally. australis (which also occurs in Australia) and Other items eaten included Amphipoda, Anguilla die, ffenbachii in the Glentui River, Cladocera, Ostracoda and Decapoda ( Canterbury, New Zealand. Crustacea), Odonata, Coleoptera, Diptera, With few exceptions, the same food organisms Trichoptera and Hemiptera (Insecta) and were utilised by all fish species, but the gastropod molluscs. relative proportions of each food type in the At the end of their first three months in the diet varied between species. Kendall rank lake, the salmon had increased 85% in length correlation coefficients indicated that the diets and 670% in weight. After two years in the of native fish were dissimilar, with the lake, their mean length was 582 mm and their exception of galaxiids and bullies in autumn, mean weight was 2.73 kg. Growth rate was but in six out of nine comparisons involving lowest in spring when the relative amount of the introduced trout, the coefficients indicated fish in the stomach contents was at its lowest varying degrees of similarity with the diets of and there was a greater diversity of food types the native species. in the diet. The availability of fish, particularly Since their feeding mechanisms and feeding G. maculatus, appeared to be the major factor localities were different, similarities in the diets affecting the growth of chinook salmon in Lake of eels and trout, bullies and trout, and bullies Purrumbete. It was thought that G. maculatus and galaxiids were regarded as having the moved from the lake into inflowing intermittent potential to give rise to indirect competition (i. streams for spawning during late winter and e. where there is no contact between spring, so they were not available as food for individuals). However, since trout (up to 200 the salmon at that time of the year. mm long) and galaxiids occupied the same The food of rainbow trout (up to 6.6 kg in microhabitat and fed in the same manner, weight and 725 mm long) taken at the same similarity in their diets was regarded as having time as the chinook salmon contained a much the potential to give rise to direct competition ( wider range of food types than the salmon ( i.e. where there is contact between individuals). Cadwallader and Eden 1982). However, of the fish eaten, all were G. maculatus, with the Jackson (1978) exception of a few N. australis taken on one In a study of the benthic invertebrate fauna occasion. An earlier field investigation of the and the diets of brown trout and river food of rainbow trout in April 1967 revealed blackfish Gadopsis marmoratus in the that galaxiids had formed a substantial part of Aberfeldy River, Victoria, over a 12-month the diet of the trout, with 708 galaxiids being period, Jackson (1978) found that the range of recorded from 28 trout (mean of 25 per food organisms utilised by the two species was stomach; range very similar, as were the proportions of 12-47). Unfortunately, during April 1977, only eels Anguilla dieffenbachii, bullheads (family eight rainbow trout were taken. These fish, Eleotridae), Galaxias paucispondylus and which had similar length and weight ranges to Galaxi.as brevipinnis (which also occurs in the trout taken in 1967, had eaten 80 Australia). galaxiids (mean of 10 per stomach; range 1- The proportions of the various benthic 25). Although the number of trout in the invertebrates in the diets of two of the April 1977 sample was small, these figures bullheads, eels, G. brevipinnis, G. nevertheless suggest that galaxiids were less paucispondylus and juvenile brown trout were common in the diet of the rainbow trout in similar to the proportions of the prey items in Lake Purrumbete than they were in 1967. the benthos. Deleatidium (Ephemeroptera) Some extremely large rainbow trout had been and chironomid (Diptera) larvae dominated the produced in Lake Purrumbete. Wharton (1967) -benthos in all seasons and formed the bulk of reported yearling trout from the lake weighing the food of these_ species. Overlap in diet was 1.4 kg, 3-year-olds weighing 8.4 kg and 4- high, suggesting potential for competition, year-olds weighing 9.3 kg. These growth rates but preferred habitat and differences in were considered world records for rainbow feeding habits, together with low fish trout at the time and reflected an excellent population density and the abundance of the food supply. Such growth rates no longer main prey items, were thought to "eliminate occurred in the lake and this was attributable the occurrence of any serious competition". to the reduced availability of G. maculatus. The diet of chinook salmon differed from the Anecdotal reports from anglers and local other species; it consisted largely of prey items residents suggested that G. maculatus (a well of terrestrial origin, including adult recognised, popular, local bait species) was Deleatidium and dipterans. much less common in the lake at the time of the study than formerly. Furthermore, smelt Glova (1990) Retropinna semoni were recorded in the lake Glova (1990) commented that while there was previously, but none were taken during the little doubt that competition for food and space present study. occurred between galaxiids and salmonids, Predation by both chinook salmon and these impacts were probably of minor rainbow trout had most probably affected the importance compared to that of predation. In abundance of G. maculatus in Lake particular, galaxiid fry tended to shoal in large Purrumbete. Stocking densities of trout in the numbers in the water column in areas of slack past (1958-67) were generally less than in the water, making them easy prey for yearling and years before this study (1969-76), so growth older trout. As stream- . dwelling galaxiids got rates and the number of galaxiids per trout older, they tended to become cryptic bottom- stomach could well have been directly related dwellers, which probably made them less easy to differences in stocking density, both being targets for trout to prey upon. affected by the number of salmonids present To test the hypothesis that free-swimming at a given time. Neither chinook salmon nor prey were more vulnerable to predation by rainbow trout bred in Lake Purrumbete, their trout than bottom-dwelling prey, Glova numbers depending solely on releases of carried out three sets of short-term hatchery-produced fish. Under these experiments in glass tanks. The first set of circumstances, it was concluded that tanks had a simple gravel substrate, the introduced salmonids were unlikely to second set had a more complex gravel and eliminate the galaxiids from the lake unless cobble substrate, and the third set had a the lake was mismanaged by overstocking with complex substrate with gravel, cobbles and trout or salmon or both. a submerged willow branch. For each set of tanks, a control tank was used to determine Sagar and Eldon (1983) mortality of the prey in the absence of Sagar and Eldon (1983) investigated the predation. benthic macroinvertebrate fauna and the food and feeding relationships of several small fish in the unstable, braided Rakaia River, New Zealand, over a 12-month period. The fish species included juvenile brown trout, chinook salmon, long-finned

32 The free-swimming prey were fry of Galaxias species. Small prey items made up a greater vulgaris (similar in many respects to the proportion of the diet of G. brevipinnis than for Australian Galaxias olidus) and the bottom- either trout species. The narrower breadth of dwelling prey were juvenile bullheads of the the diet of G. brevipinnis in this study compared family Eleotridae. to the more diverse diet reported by other A yearling trout, about 150 mm long, was researchers was thought by Glova and Sagar to placed in each of the tanks, followed a day later perhaps indicate that the feeding of G. by 20 each of the two prey types. The galaxiid brevipinnis in the Ryton River was restricted to fry were 22-42 mm long, and the juvenile some extent by their interaction with trout. bullheads 34-49 mm long. The same number of All three species were found primarily in riffles each prey type was included in each control and runs in water depths of 0.1-0.3 m with G. tank, but with no trout present. The brevipinnis often being in faster flowing areas ( experiments were terminated on the day when water velocity 0.8-1.1 m per sec) than either only one live galaxiid fry remained in the water brown trout and rainbow trout (0.4-0.7 m per column, which varied from four to nine days sec). Glova and Sagar concluded that these after the start of the experiment. differences in diel feeding patterns and The results were as predicted, with young free- microhabitat no doubt reduced the interaction swimming galaxiids eaten in greater proportion between the galaxiids and trout. than the bullheads. Predation was greatest and fastest for both prey types in the tank with the Kusabs and Swales (1991) simple substrate (92 galaxiids/66 bullheads), Kusabs and Swales (1991) examined the diet of and was reduced markedly by adding cobbles sympatric populations of migratory juvenile to the substrate (77 galaxiids/40 bullheads). rainbow trout and Galaxias brevipinnis (which The addition of the willow branch did not also occurs in Australia) in the Waipehi and reduce predation as expected (85 galaxiids/63 Omori Streams, which drain into Lake Taupo, bullheads), probably because it did not provide New Zealand. a sufficiently complex environment, and the The diets of both species were dominated, both trout may have hid in it, making it easier to numerically and by weight, by aquatic prey, ambush prey. It was thought that not all the with ephemeropteran, trichopteran and galaxiid fry were eaten by trout; the losses of dipteran larvae being the most numerous prey galaxiids in the controls was on average 27%, items. Adult G. brevipinnis and juvenile indicating that the bullheads may have been rainbow trout both fed on juvenile galaxiids. responsible for some of the predation on Terrestrial prey items were present in the diets galaxiids in the experimental tanks. There were of both galaxiids and trout; although present in no losses of bullheads in the controls. low numbers they were important in terms of weight. Resource partitioning was found to be Glova and Sagar (1991) weak, although G. brevipinnis ate more small Glova and Sagar (1991) studied the benthic benthic invertebrates such as chironomid and drifting invertebrates, together with the larvae, whereas the rainbow trout took more fish, in the Ryton River, New Zealand, over a ephemeropteran larvae and terrestrial insects. 24-h period during summer in order to In Waipehi Stream, G. brevipinnis ate both investigate interactions for food and space rainbow trout ova and G. brevipinnis ova; in between Galaxias brevipinnis (which also Omori Stream trout ova were taken by the occurs in Australia) and juvenile brown trout juvenile rainbow trout. and rainbow trout. Since the diets of G. brevipinnis and juvenile Galaxias brevipinnis fed almost exclusively at rainbow trout in these Lake Taupo inlet night on the benthos, whereas both brown streams were similar, Kusabs and Swales trout and rainbow trout juveniles fed mostly concluded that the populations may co-exist during the day on drifting and benthic prey. by temporal and/or spatial partitioning of food Larvae of Deleatidium (Ephemeroptera), resources, whereas predation by adult trout Hydrobiosis and Oxyethira (Trichoptera), and on small G. brevipinnis may be a limiting factor Austrosimulium and Chironomidae (Diptera) for G. brevipinnis populations. formed the bulk of the prey of all three Crowl et al. (1992) The authors suggested that the slight Crowl et al. (1992) reported that in a series of differences in feeding times, diets and laboratory experiments all sizes of Galaxi.as microhabitats were important in reducing vulgaris (very similar in many respects to competitive interactions between co- Galaxias olidus) were vulnerable to predation occurring populations of G. vulgaris and by brown trout. Very young galaxiids were brown trout. especially vulnerable to predation by young trout, with consumption rates of up to 135 Glova and Sagar (1993) galaxiids per day. Even the largest galaxiids Glova and Sagar (1993) examined the feeding were vulnerable to larger brown trout (up to and spatial inter-relations between two 200 mm long). galaxiids, Galaxias vulgaris (similar in many This study, like that of Glova (1990), can be respects to the Australian Galaxias olidus) and criticised on the grounds that the experimental Galaxias paucispondylus, and juvenile brown conditions bear little resemblance to conditions trout and chinook-salmon in Deep Creek, a in nature, but they both demonstrate that trout tributary of the upper Rangitata River in the consume native fish and that predation rates South Island of New Zealand. Fish were can be exceedingly high. sampled by electrofishing. Interspecific overlap in the timing of feeding of Glova et al. (1992) the four species was greatest between predusk Glova et al. (1992) investigated the feeding and and pre-dawn. Aquatic invertebrates were spatial inter-relationships between juvenile eaten by all fish, with the chinook salmon also brown trout and Galaxias vulgaris (very similar taking trichopteran imagoes. Similarities in in many respects to Galaxias olidus) over a 24- diets were least between G. vulgaris and G. h period during summer in Weydon Burn, a paucispondylus, moderate between the small tributary of the upper Oreti river in the galaxiids and salmonids, and greatest between South Island of New Zealand. Fish were the two salmonids. sampled by electrofishing. The mean sizes of Both galaxiids were found primarily in riffles, the galaxiids and the juvenile trout in the with G. uulgaris occupying slightly deeper (up samples were similar. to 0.3 m) and slower (0.5-0.8 m/sec) waters Interspecific overlap in feeding was found to be than those occupied by G. paucispondylus (up greatest at dusk and dawn, with G. vulgaris to 0.2 m; 0.7-1.0 m/sec). The salmonids were feeding primarily from dusk to postdawn and found mainly in pools and runs, with the juvenile trout feeding primarily from pre-dawn chinook salmon occupying slightly deeper (up to post-dusk. Both galaxiids and trout fed to 0.5 m) and slower (0.1-0.2 m/sec) waters mainly on benthic and drifting aquatic than those occupied by brown trout (up to 0.4 invertebrates, with larval Deleatidium ( m; 0.2-0.5 m/sec). Ephemeroptera), Hydora (Coleoptera) and The authors concluded that that mixed Chironomidae (Diptera) being the preferred populations of galaxiids and juvenile prey, although trichopteran imagoes also salmonids in streams with a gravel/cobble formed an important part of the diet of juvenile substrate were likely to overlap considerably trout. in their use of food and space, but that The stream channel at the study site was about interspecific differences in feeding and 4-7 m wide, with extensive areas of shallow microdistribution reduced interactions riffles and runs and relatively unstable bed and between the galaxiids and salmonids. banks composed mainly of gravel and small cobbles. Galaxiids and trout were found in both Gillespie (1995) riffles and runs, with the galaxiids occupying Gillespie (1995) pointed out that frogs which slightly shallower (up to 0.3 m) and faster (0.3- coexist with fish, such as those living in 0.7 m/sec) waters than did trout (up to 0.5 m; streams, have evolved strategies for avoiding or 0.2-0.4 m/sec). minimising predation on their tadpoles. These strategies may include laying eggs in inaccessible places, activity patterns which are different from the activity patterns of fish and the production of unpalatable or poisonous chemicals. In many instances, fish species have been found not to eat the

34 tadpoles with which they coexist. However, 1910-1911 to about 1 kg in 1917. This decline these strategies may not be effective against has been attributed to a decline in the number introduced species, which may forage in of G. brevipinnis as a result of trout predation. different ways, be more effective predators or Further evidence that the decline of G. be unaffected by the chemicals produced by brevipinnis is related to trout predation is the tadpoles. Therefore, tadpoles of some provided by the abundance of these galaxiids in amphibian species may be vulnerable to other lakes where trout have not been increased predation pressure from introduced introduced (McDowall 1987). A summary of fish such as trout. the food of trout in New Zealand waters is given In laboratory feeding experiments, it was by McDowall (1990a), and comments and found that brown trout ate the tadpoles of observations on the effects of trout feeding and three species of frog, whereas Galaxias olidus, predation on the New Zealand fauna are which coexists with the three frog species in reviewed by Thomson (1922), Phillipps (1940), nature, did not eat any of the tadpoles of Allen (1961), Waugh (1973), McDowall (1984, these three species. The author indicated that 1987, 1990a, b, c). and Crowl et al. (1992). further investigation of the effects of trout on tadpoles is required, but speculated that trout have probably had a substantial impact on 3.5 Behavioural Studies frogs in south-eastern Australia. Glova (1989) Other Observations and Comments Glova (1989) reported that behavioural studies Tilzey (1977) pointed out that even though had provided some insight into the potential angling and scientific records for the years impact of salmonids on native fish stocks, and immediately following the introduction of trout mentioned that in various stream simulation into Australia (1870-1910) are scarce, they projects he had observed that juvenile indicate that the trout at that time were salmonids were generally behaviourally substantially larger than those taken from the dominant over various galaxiid species. same waters today, and that such growth Galaxiids entering the territories of salmonids probably reflected low trout population were invariably threatened, chased or nipped in densities and an abundant food supply. an effort to make them leave or retreat into the Lyne (1948) mentioned that in 1897 a brown substrate. Occasionally galaxiids were observed trout of 6.6 kg was taken in the Yarra River, to fight back by charging and nipping their and provided an anecdotal description of what attackers, but seldom did they win in the end. conditions in southern Victorian, streams Glova pointed out that there was now good would have been like at the time. Native fish evidence that juvenile salmonids were such as galaxiids, grayling and smelt would territorially-active only during daylight, have abounded, but having no innate defence whereas most galaxiids and other New Zealand mechanisms to avoid such "a fast and fish species were active at night. Typically, the ferocious feeder" as the trout they would have native fish became active at dusk, and at dawn been soon thinned out. The food supply was they retreated to the substrate, so that direct not sufficient to withstand the ever-increasing interactions between galaxiids and salmonids natural reproduction and artificial stocking of in nature may be limited primarily to twilight trout, and the large fish gradually disappeared conditions. to be followed by fish of a much smaller average size. McIntosh et al. (1992) The early prodigious growth of trout in the McIntosh et al. (1992) investigated lakes of the central North Island of New microhabitat used by Galaxias vulgaris (very Zealand has been attributed to the similar in many respects to Galaxias olidus) in abundance in these lakes of Galaxias the presence and absence of brown trout in brevipinnis, which declined dramatically the Shag River, New Zealand. following the introduction of trout. In Lake Several microhabitat variables were measured Taupo the high quality of the trout at random locations where G. vulgaris was deteriorated rapidly in the years after they present during the day. The galaxiids were established, the average weight of preferred coarse substrates, using rainbow trout dropping from 4 kg in them as resting places, but showed no other proportion of its behaviour that was inactive, microhabitat preferences. This pattern of either during the day or night, but the relative microhabitat use did not change in the frequency of FS postures increased at both presence of brown trout although galaxiid times. Type C galaxiids exhibited more active densities were considerably lower. behaviour both during the day and at night, The field observations were followed by but the relative frequency of cryptic FS experiments using trout (120-150 mm long) and postures was greater during the day than at galaxiids (75-85 mm long) in six artificial night. The proportions of galaxiids feeding were stream channels constructed from 2 m long reduced for all types A, B and C, but was least sections of 400 mm-diameter PVC stormwater marked for type C. Feeding rates were reduced pipe cut in half longitudinally. Each channel during both day and night for types A and B, was fitted at each end with 5 mmdiameter but not for type C. stainless-steel mesh and was covered by a The authors acknowledged that the tightly-fitting perspex lid. The channels were behaviour of both galaxiids and trout could positioned in pairs in three riffle areas of the have been modified by the artificial Silver Stream about 80 m apart. They were conditions of the experiment. However, their secured in position using steel stakes and were results indicated that the galaxiids modified placed so that, during base flow, water flowed their behaviour in the presence of trout, and evenly through the channels at a depth of 150 that the three genetic types responded mm. All channels received similar water flows. differently. Drift nets set inside and beside the channels showed that food availability inside the channels was similar to that outside. 3.6 Studies on the Disease Experiments in the channels confirmed that competition for space did not occur during the Impacts of Salmonids day even at high galaxiid densities. However, Introductory Comments the situation changed dramatically at night, In the early days of fish introduction, prolonged with the galaxiids spending significantly more transport times may have contributed to the time in slower areas when trout were present. death of eggs carrying disease or infectious Since G. vulgaris fed on drifting invertebrates, agents. Faster transport eliminated the time McIntosh et at. concluded that brown trout factor, making it more likely that diseases could could affect the galaxiids deleteriously by be introduced with fish and eggs (Ashburner forcing them to occupy less profitable feeding 1976). However, Australia still appears to be free positions. Further, they speculated that of most of the serious pathogens which affect interspecific competition for space, combined salmonids in many other countries (Humphrey with competition for foodand predation by 1985). To maintain this situation, there is a trout, could explain observed declines in G. total ban on imports of trout and salmon vulgaris populations. products, other than those canned or hot Edge et al. (1993) smoked, although this ban is constantly Edge et al. (1993) investigated the antipredator challenged by foreign exporters (Kailola et al. behaviour of three genetic types of Galaxias 1993). vulgaris (very similar in many respects to The importation of live fish and eggs is the Galaxias olidus) in the presence of brown trout most efficient way of importing pathogens for in two, recirculating stream channels. Fish that species. Imported- fish bring with them - behaviour was recorded using photography and not only pathogens specific to them, but also a video recorder. pathogens which may affect other fish or they The responses of the three genetic types (A, B may be hosts and vectors for pathogens found and C) of G. vulgaris to trout differed. Type A - previously in other organisms (Langdon 1988a) galaxiids exhibited more inactive behaviour ( . Furthermore, infectious agents maybe more increasing the frequency of the cryptic "flat on pathogenic in atypical hosts than in typical the substrate" posture, FS) during the day, but hosts, and may cause major disease outbreaks not at night. Type B galaxiids showed no when atypical hosts come into contact with significant effect of trout on the typical hosts (Langdon 1989b).

36 Although the likely role of introduced fish in Saville-Kent (1888) introducing and disseminating fish diseases in The remarks made by Saville-Kent (1888) in Australia is well described (Fletcher 1986, relation to the impact and origin of the fungus Langdon 1988b, 1989b, Morison 1988), most Saprolegnia are extremely interesting. He research has been focused on the pointed out that the fungus occurred each identification and treatment of diseases in breeding season at the salmon hatchery on the aquaculture (Ashburner 1983, Humphrey and River Plenty (where brown trout and Atlantic Langdon 1985, Rowland and Ingram 1991). salmon had been held since 1864). On some Furthermore, as new pathogens are occasions, it was said to be "so abundantly discovered, it is becoming increasingly difficult developed as to constitute a veritable epidemic to determine whether they originated from which may be communicated to apparently introduced fish or from native fauna (Fletcher healthy fish". 1986). Saville-Kent then went on to consider the It is assumed that parasites such as apparent epidemic some 17-18 years previously Ichthyophthirius multiftlis, which causes white which had caused the demise of the Australian spot disease, and Ichthyobodo necator ( grayling Prototroctes maraena. The grayling formerly Costia necatrix) were brought into were said to "have been seen floating down the Australia with live fish some time between rivers in thousands, covered more or less 1880 and 1930 (Ashburner 1976). Whether extensively with a cottony fungoid growth. So they were introduced with salmonids or with virulent and exhaustive was this epidemic that other fish species, or with both salmonids and many, more especially of the southern rivers, other species, is debatable and perhaps will were more or less completely denuded of their never be known. Butcher (1941) attributed an stock of this species and have so remained up outbreak of white spot disease, which caused to the present date". Saville-Kent posed the massive mortalities in trout at the hatchery of questions of how, when and where the the Ballarat Fish Acclimatisation Society, to epidemic originated and whether at the time ornamental carp. An earlier outbreak of the there were any abnormal conditions associated disease (apparently not associated with the with the rivers carrying the infected fish. He presence of carp) had been reported in trout at went on to say: "The approximate date of the the Plenty Hatchery in Tasmania in 1933 ( appearance of this epidemic would appear to Butcher 1941, Ashburner 1976). Similarly, be about the year 1869 or 1870, periods it may Saville-Kent (1888) and Hardy (1910) reported be remarked of great activity in association fungal infections at the Plenty and Studley with the distribution of the fry of the newly Park (Melbourne) salmonid hatcheries acclimatised Salmonidae in the rivers of this respectively. colony. Is it possible ...that the fungus, Whether pathogens were introduced into Saprolegnia, was hitherto unknown to Australia with salmonids or not, the Tasmania and was introduced with the ova of widespread stocking of salmonids, mainly these Salmonidae, or more probably in the trout, by the Ballarat, Plenty, Studley Park moss wherein they were packed? Under such and, later, other hatcheries would have spread conditions the germs or spores, like the parasites such as I. multif its and other microbes of measles or smallpox, arriving on a pathogens widely throughout Tasmania, virgin and congenial soil, might be expected to Victoria and New South Wales, then to South spread with devastating virulence among the Australia and Western Australia. aboriginal inhabitants." Unfortunately, there have been few studies on the role that hatchery-produced salmonids Parisot et al. (1965) have played in acting as vectors for the In July 1963, a batch of chindok salmon eyed dissemination of the wide range of protozoan, eggs was sent by air from the Coleman Fish metazoan, bacterial and fungal pathogens Hatchery on Battle Creek, a tributary of the typically found in Australian salmonid Sacramento River in northern California, USA, hatcheries (Ashburner 1978, 1983, Humphrey to the Victorian State Fish Hatchery at Snobs and Langdon 1985) or on other possible Creek. The eggs hatched normally in August disease impacts of salmonids on the Australian and at the "swim-up "stage in September the fauna. The few studies which have been fry appeared normal. However, undertaken are reviewed here. a sudden rise in mortalities occurred about Pollard (1974) ten days after the fry started feeding. The Pollard (1974) found that Galaxias maculatus moribund fry were reported to have pale gills in landlocked Lake Modewarre, southern and a red blotch on the skin in front of the Victoria, was infected with Ligula, a parasitic dorsal fin. Haemorrhages were seen in some cestode, and Eustrongylides, a parasitic cases on the side of the fish below and behind nematode. the dorsal fin and stretching to the ventral Ligula was present as the plerocercoid stage in surface, on the opercles and on the the coelomic cavity of the galaxiid. The mean branchiostegal skin. The disease outbreak percentage weight of plerocercoids per infected fish lasted for three weeks and resulted in losses was about 9% (maximum 50%) of the intact of about 11%. host weight. The mean number of plerocercoids According to Parisot et al. (1965), except for per infected fish was 1.5, the maximum number the lateral haemorrhaging, the symptoms per fish being five. The mean incidence of were almost a classic description of infection was 50%. The effects of these cestodes Sacramento River chinook disease on the host galaxiids included a reduction in (= infectious haematopoietic necrosis or IHN - general body condition, an inhibition of gonadal J. D. Humphrey, Australian Animal Health maturation, and an inhibition of movements to Laboratory, pers. comm.). Subsequently, all the spawning areas during the breeding season. fish in the infected batch at the Snobs Creek Eustrongylides was usually found encysted in Hatchery were destroyed and the disease has the visceral peritoneum. The mean number of not recurred. nematodes per infected fish was 5.4, and the maximum number per fish was 44. The mean Ashburner and Ehl (1973) incidence of infection was 80%. One of the Ashburner and Ehl (1973) reported the effects of this nematode on its host was the occurrence of the parasitic protozoan inhibition of egg laying by female fish when the Chilodonella cyprini on brown trout held at nematode was encysted in the ovary or vent. In the Victorian State Fish Hatchery at Snobs Lake Modewarre, Eustrongylides was also Creek, the parasite normally being found on found in rainbow trout and an eleotrine goby the gill filaments of the trout. It was found to and, and a similar form (thought to be an cause little or no damage to adults, but in fry ( intermediate-adult stage of the same species) 20-40 mm long) heavy mortalities associated was found in a cormorant. with gill hyperplasia resulted from as few as The finding of Ligula in the Australasian two or three of the protozoans per gill region constituted a new zoogeographic record, filament. and its occurrence in G. maculatus constituted The stocking of waters with infected trout a new host-family record. Regarding the origin would have assisted in the spread of C. of the Ligula infecting these landlocked cyprini throughout Victoria. Fish samples galaxiids, and thus the presence of this taken in Victoria during the previous ten parasite in the Australasian region in general, years had shown that C. cyprini occurred on Pollard speculated that possible agents for its several native and introduced fish species. introduction were the brown trout, rainbow Infected native fish included galaxiids, trout and redfin perch Perca fluviatilis, all of Australian smelt Retropinna semoni, which have been introduced into Lake Macquarie perch Macquaria australasica, Modewarre and all of which have been Murray cod Maccullochella peeli, trout cod recorded as a host of Ligula in the Northern Maccullochella macquariensis, southern Hemisphere. The arrival of Ligula in pygmy perch Nannoperca australis, river Australasia via a migratory bird host would be blackfish Gadopsis marmoratus, and striped much less likely because of its short adult life- gudgeon Mogurnda adspersa; infected cycle stage in the bird (less than five days) introduced fish included brown trout, compared with the fish host , (up-to 12-14 rainbow trout and goldfish Carassius months). auratus.

38 Ashburner (1977) for salmonids, with Atlantic salmon being the Ashburner (1977) described the incidence of most susceptible and rainbow trout the least mycobacteriosis in hatchery-confined chinook susceptible of the salmonids tested. salmon derived from a presumed "disease- Furthermore, the organism was transmitted free" consignment of 50,000 eyed eggs from inoculated fish to within-tank control received at the Victorian State Fish Hatchery fish via water and established a carrier state at Snobs Creek from Oregon, USA, in 1966. in Atlantic salmon. Before the salmon eggs were imported, Similarly, Carson and Handlinger (1988) found mycobacteriosis had not been observed at that an atypical strain of A. salmonicida Snobs Creek, although other acid-fast bacteria isolated from goldfish with cutaneous (Nocardia) had been isolated from rainbow ulcerative lesions proved to be highly virulent trout. Mycobacteria appear to have been to Atlantic salmon challenged by introduced with the eggs, particularly since intraperitioneal injection and by bath the strains appear similar to those isolated in immersion. The salmon developed lesions the USA. The possibility that the infection was bearing a close resemblance to classical transmitted to the salmon in the food they furunculosis in salmonids. received at Snobs Creek was ruled out because Although this atypical strain of A. salmonicida no cases of mycobacteriosis were found in the was introduced into Australia via goldfish hatchery stocks of brown trout and rainbow imported from Japan in 1974 (Humphrey and trout which at the time were fed on the same Ashburner 1993), it is likely to be food as the salmon. It is also unlikely that the disseminated by both goldfish and salmonids. salmon contracted the disease from their Whittington and Cullis (1988) and Carson and immediate surroundings, which were Handlinger (1988) predicted that outbreaks of indistinguishable from those of the trout held furunculosis in salmonid fish are likely to at Snobs Creek. occur in south-eastern Australia if this strain Ashburner reported that it took two years for of A. salmonicida is transmitted from goldfish the number of mycobacteria to increase to with GUD to salmonids. They concluded that readily detectable numbers, but noted that the the organism posed a significant threat to the incidence of infection decreased in subsequent aquaculture industry and wild salmonid stocks year-classes. The occurrence and effects of in Australia. Its potential impact on native mycobacteria in the Goulburn River system, in fauna is unknown. which Snobs Creek is located, or in Lakes Purrumbete and Bullen Merri, in which Langdon et al. (1988), Langdon ( chinook salmon derived from the Oregon 1989a, b) shipment of eggs were stocked, is unknown. Langdon et al. (1988) reported two outbreaks of a disease in hatchery-confined rainbow trout Whittington and Cullis (1988), Carson caused by the epizootic haematopoietic and Handlinger (1988) necrosis (EHN) virus of redfin perch Perca Whittington and Cullis (1988) found that an fluviatilis which was first isolated in north- atypical strain of the bacterium Aeromonas eastern Victoria in 1984. The outbreaks in salmonicida, which causes goldfish ulcer trout represented the first verified instance of a disease (GUD), had attributes typical of viral disease in Australian salmonid stocks. virulent, typical strains which cause Extensive virological surveys using appropriate furunculosis in salmonids. They isolated the techniques had previously failed to detect bacterium from diseased goldfish Carassius viruses or viral diseases in salmonids (Langdon auratus in Australia and inoculated it into et aL 1986). Atlantic salmon, brown trout, rainbow trout Langdon (1989a) subsequently found that and brook trout by intraperitoneal injection several native species, viz. Macquarie perch and by bath immersion. The results of their Macquaria australasica, silver perch Bidyanus experiments demonstrated that the strain of A. bidyanus and the galaxiid Galaxias olidus were salmonicida in populations of goldfish in all highly susceptible to the virus; Murray cod south-eastern Australia is highly pathogenic Maccullochella peeli was a potential carrier, and golden perch Macquaria ambigua and Australian bass Macquaria novemaculeata were considered unlikely to be naturally susceptible hosts. He considered that carrier individuals of redfin perch, rainbow estuarine as well as freshwater habitats, the trout and Murray cod, and possibly other fish, studies cover a relatively small part of the represented a further reservoir of infection. This native fish fauna. case illustrates the hazards of transmission of The most substantive evidence of impacts of infectious diseases between different families salmonids in Australia comes from Fletcher's ( and species of fish, and the risks of moving fish 1979) experimental introduction study and the from one area to another. Langdon observations of Tilzey (1976), Raadik (1993) recommended that translocations of P, and Closs and Lake (in prep) during the fluviatilis, salmonids, percichyids and invasion of trout into new areas. Much of the teraponids at least should be subject to health information on the distributions of salmonids certification of freedom from EHN virus. and native fish presented in section 3.1 was Further, Langdon (1989b) pointed out that derived from general fish surveys not although the EHN virus was not introduced specifically undertaken to investigate the into Australia with the naturally susceptible effects of salmonids on particular species or redfin or salmonids, it had been spread aquatic communities. Exceptions to this insidiously by their translocations on approach were the studies of Jackson and mainland south-eastern Australia. For Williams (1980) and Ault and White (1994). example, hatchery-reared trout infected by Jackson and Williams .(1980) compared the wild redfin were moved from the upper distributions of native fish in areas with and Murray catchment to the upper without trout. It was apparent that when trout Murrumbidgee drainage where the disease were present, galaxiids such as Galaxi.as olidus had since occurred on a trout farm. and Galaxias brevipinnis were restricted to the upper reaches of river catchments in areas Davies (1991) which were inaccessible to trout. However, The bacterium Yersinia ruckeri is responsible when trout-were absent, galaxiids were not for enteric redmouth disease, an acute and restricted to such areas. Observations made by chronic infection of salmonids, and has been Closs and Lake (in prep) in their invasion known to exist in Australia since the 1960s. study indicated that as trout moved Davies (1991) reported two clonal types of Y progressively upstream the galaxiid population ruckeri from Australia, one of which appeared became progressively fragmented, giving rise to to be unique to Australia and one of which a series of isolated populations, and producing shared characteristics with isolates from the type of trout/galaxiid distribution pattern Europe and the USA, suggesting that at least described in many of the distribution studies one biotype of Y ruckeri was introduced with presented in section 3.1. Ault and White ( salmonids or their eggs (J. D. Humphrey, 1994), using a similar approach to that Australian Animal Health Laboratory - pers. adopted by - Townsend and Crowl (1991) in comm.). The effect of Y ruckeri on native New Zealand, were able to demonstrate that Australian fauna is unknown. the presence of brown trout rather than habitat characteristics was responsible for the observed distribution of Galaxias truttaceus in 3.7 Overview of Studies on their study streams. Taken together, the numerous and widespread Impacts of Salmonids instances of fragmented galaxiid distribution Studies on the impacts of salmonids on patterns in the presence of trout (in a wide Australian fauna reviewed in sections 3.1-3.6, range of catchments, some in areas of natural including New Zealand studies on Galaxias vegetation, some in cleared areas), the more brevipinnis but excluding those on taxa not widespread distribution of these galaxiids in found in Australia, are listed in Table. 2. It is the absence of trout, and the observations of immediately apparent that there have been few fragmentation of the galaxiid distribution studies on or relating to the impacts of pattern as trout progressively move upstream, salmonids on fauna other than fish and, provides a substantial body of evidence for an considering the families of fish which occur in adverse impact of trout on these stream- areas in which trout have been introduced in dwelling galaxiids. Australia, including

40 Studies on the mechanisms by which requirements, are able to avoid direct salmonids have had an impact on the native encounters are likely to be able to co-exist fauna are sparse, but nevertheless indicate with salmonids. Evidence of exclusion based that predation has been the major cause of the on competition is extremely difficult to impact. This is hardly surprising given the demonstrate in field situations. However, the large size to which salmonids can grow and the few studies which have been done on the relatively small size of individuals in families interactions between stream-dwelling such as the Galaxiidae, which appears to have galaxiids and salmonids in artificial stream been the fish family most affected by channels indicate that competitive exclusion salmonids, at least on the basis of the present of galaxiids by salmonids can occur. evidence. The impact of salmonids on the native fauna The studies which have been done on the via the spread of pathogens, particularly via interactions between juvenile salmonids and the widespread releases of hatchery-produced the native fauna indicate that direct fish, is unknown. However, the occurrence of competitive encounters may occur between pathogens in salmonid hatchery stocks juvenile trout and those species which occupy indicates that salmonids have undoubtedly the same microhabitat and feed in the same played a major role in the spread of these manner on the same foods. Conversely, those disease organisms, irrespective of whether or native species which, because of their not the pathogens were introduced into particular life histories and habitat Australia with the salmonids. Table 2. Studies on impacts of salmonids on Australian fauna. Author(s) Native fauna Salmonid species

Saville-Kent (1888) Prototroctes maraena brown trout/Atlantic salmon Gray (1929) Whitley ( Galaxias brevipinnis rainbow trout trout brown trout 1935) Williams (1964) galaxiids brown trout Frankenberg (1966, 1969) Galaxias brevipinnis Morrissy (1967) brown trout/rainbow trout Galaxias olidus brown trout/rainbow trout Galaxias olidus brown trout/rainbow trout Cherax destructor brown trout/rainbow trout tadpoles brown trout/rainbow trout Dytiscidae brown trout Gyrinidae brown trout Renowden(1968) Galaxias brevipinnis brown trout/rainbow trout Ashburner and Ehl (1973) several fish species trout Pollard Andrews ( (1974) Galaxias maculatus trout 1976) Knott et al. (1978) Galaxias brevipinnis rainbow trout Tilzey (1976) Anaspides tasmaniae brown trout/rainbow trout Galaxias olidus brown trout Fletcher (1979) Galaxias brevipinnis brown trout Jackson (1978) Galaxias olidus brown trout Cadwallader (1979) Gadopsis marmoratus brown trout Jackson and Williams (1980) Galaxias olidus brown trout Galaxias olidus chinook salmon Cadwallader and Eden (1981) rainbow trout Cadwallader and Eden (1982) Galaxias brevipinnis brown trout Jackson and Davies (1983) Galaxias maculatus Sagar and Eldon (1983), NZ Galaxias maculatus brown trout Koehn (1986a) Koehn (1986b) Galaxias olidus brown trout Davies (1989) Galaxias brevipinnis brown trout/rainbow trout Humphries (1989) Galaxias olidus brown trout Langdon (1989a, b) Galaxias maculatus brown trout Jones et al. (1990) "non-trout" species rainbow trout Koehn and O'Connor (1990) Galaxias auratus brown trout/rainbow trout Lintermans and Rutzou (1990) several fish species brown trout Glova and Sagar (1991), NZ Galaxias olidus Galaxias rainbow trout brown trout/rainbow trout Kusabs and Swales (1991), NZ brevipinnis Galaxias Sanger and Fulton (1991) rainbow trout brown trout olidus Galaxias brown trout brevipinnis Galaxias brown trout brevipinnis Galaxias trout Sloane and French (1991) fontanus Galaxias brown trout/rainbow trout Shirley (1991) Hamr (1992) brown trout Raadik (1993) Ault and johnstoni Galaxias rainbow trout White (1994) Gillespie ( tanycephalus brown trout 1995) Closs and Lake (in galaxiids brown trout prep) Galaxias fuscus brown trout Galaxias pedderensis Galaxias fuscus Galaxias truttaceus tadpoles Galaxias olidus

42 4. CRITIQUE OF RESEARCH METHODS, RECOMMENDATIONS ON METHODS AND PRIORITIES FOR RESEARCH, AND MANAGEMENT ACTIONS 4.1 General Considerations 4.2 Review of Experimental Taylor et al. (1984) pointed out that although Methods and the effects of introductions may not be in doubt, at least on theoretical grounds, rigorous Recommended documentation of specific examples of impacts is generally lacking because investigators have Approaches for not accommodated the consequences of Investigating the Impact multiple causality in the design of impact studies. The demonstration of an impact by an of Salmonids on Native introduced species on a native species requires Fauna verification of a causal relationship between Future studies of distributions or, more observed or measured changes in a population specifically, mutually exclusive distributions of of the native species and the presence of the salmonids and native species in Australia, introduced species. This requires an should adopt the approach taken by Townsend experimental design with appropriate controls and Crowl (1991). Their statistical analyses and replicates. As pointed out by Morison ( incorporating various physical, chemical and 1988), such experimental manipulations can biological variables from a large number of seldom be achieved in nature, so there is then a sampling sites in one catchment indicated that compromise between the need to control all the presence and abundance of galaxiids were potential variables and the need to prevent the best predicted by the presence or absence of experiment from becoming an trout rather than by any of a wide range of oversimplification and artificial representation other possible variables such as changes in of the natural situation. land use, the nature of bankside vegetation Comparison of differences in the composition of and the substrate type. Their study was natural communities between areas with and specifically designed the test the hypothesis without an introduced species can provide that the occurrence of Galaxias vulgaris was evidence for impact, but only to the extent to affected by the presence of brown trout. This which alternative causal agents can be sort of approach is much more useful than eliminated as explanations for the observed merely recording the absence of native species differences. Furthermore, such approaches do in the presence of salmonids because it not usually provide information on underlying provides information on the likely cause of the mechanisms. The occurrence of a correlation observed distribution patterns of the native between the introduction of a species and a species which presence/absence studies do not subsequent change in a native population does provide. not establish causality. Similarly, trying to The approach of Minns (1990) who analysed demonstrate an impact at a site after an the data base on freshwater fish distributions introduced species has become established in New Zealand to examine patterns of overlap lacks the controls required to demonstrate and exclusion also has merit. The main causality (Taylor et al. 1984, Morison 1988). difficulty in this approach is that information in the various State data bases may not be site- specific and, therefore, not

4 3 detailed enough to demonstrate mutually- the rocks taking up about 50% of the cage exclusive distribution patterns. Again, this volume, the remaining volume being made up approach provides no information on the by the spaces between the-rocks. Cages were cause of the observed distribution patterns left open (i.e. top removed) for an initial period, unless appropriate habitat characteristics and then five cages were sampled to provide land use information is also included in the information on initial invertebrate community data base. However, it can provide the basis structure. The remaining 15 cages were for more detailed investigations of the searched in situ for vertebrate predators which Townsend and Crowl (1991) type. may-have-colonised them (no trout were found). Introduction experiments in the field, like that A single predator (trout) was placed in each of of Fletcher (1979), provide the most convincing five cages and the top fixed to each cage; these evidence of an impact of salmonids on native were the trout inclusion cages. In another five fish. Similar experiments have also been done cages; tops were fixed without adding a trout; to examine the impacts of salmonids on these were the trout exclusion cages. The macroinvertebrates and tadpoles, e.g. see remaining five cages were left open to allow free Cooper (1988), Feltmate and Williams (1989) access of all animals in the stream. The and Andersen et al. (1993). There are many complete design was run twice, and the practical difficulties in setting up and running composition of the invertebrate community in such experiments in lotic situations, not the all cages recorded. This sort of approach has least of which is the construction and great potential for investigating the effects of maintenance of the barriers at each end of the salmonids on macroinvertebrates in Australian experimental and control sections. It is also waters. important to run the experiments over long time It is important to obtain local knowledge of the periods in order to monitor progressive changes previous history of trout in any catchment in in macroinvertebrate community structure. For which introduction experiments are example, initially, the most obvious impact may contemplated since prior occupation of an area be that galaxiids are eliminated, followed by by trout may well have already modified the some of the larger macroinvertebrates, and so structure of the aquatic community. on. Only by long-term monitoring will these Introductionexperiments in nature imply changes become apparent. It is not possible to setting up the experiment in an area in which run true replicates of this type of experiment trout have not previously occurred, e.g. as in under natural conditions because no two Fletcher's (1979) study, in a stretch of stream streams are identical. However, the experiment above a waterfall which previously had been can be repeated one or more times in nearby inaccessible to trout. In situations where streams. evidence of impact is being sought for Replicated introduction experiments could be threatened species it may be inappropriate to set up in paired raceways in aquaculture introduce trout into an area which they had not facilities such as occur in trout hatcheries. previously occupied. In such - circumstances, These units are often big enough (20-30 m one approach would be to monitor the aquatic long) to simulate sections of small streams and community in a stretch of stream in which have the advantage that the water flow can be trout occur, then remove the trout downstream regulated. to a natural or artificial barrier and monitor the Rather than investigating the effects of trout subsequent changes in the aquatic community. on macroinvertebrates by comparing the fauna This approach of removing trout is being in sections of stream with and without trout, adopted by necessity in the recovery program Reice and Edwards (1986) adopted a different for Galaxias fuscus - by Raadik (1993), but is experimental design whereby they used a also being used experimentally with Galaxias series of benthic cages some of which olidus in a small upland stream in the contained trout and some of which did not. Australian Capital Territory (M.: Lintermans, The advantage of this approach is that Parks and Conservation Service, ACT replicates can be run for experimental and Department of the Environment, Land and control treatments. Their experimental Planning - pers. comm.). In the latter situation, protocol was as follows. Twenty cages were set trout were eradicated from a section of stream in the stream substrate and filled with cobble- using rotenone, and existing barriers to sized rocks (up to 100 mm diameter), upstream movement were augmented to prevent re-

44 invasion; G. olidus are now recolonising the interest to compare the incidence of stream from which they had been previously pathogens in populations of native fish (and absent. macroinvertebrates) which have not had Data from Renowden's (1968) study on the contact with salmonids with their incidence in distribution of galaxiids and trout in pools in a populations which have had contact with small stream are presented in Table 1 as an salmonids; for example, in the case of the indication of the relatively small numbers of study by Closs and Lake (in prep), in which fish likely to be encountered in field studies of the trout population had expanded upstream the impact of salmonids on native fauna. Such then contracted downstream because of a small numbers do not detract from the value of drought, would the pathogens in the galaxiid the observations because, at the field level, fauna be any different from that in gala-)did elimination of one species by another populations which had had no contact at all ultimately involves interactions between with trout? individuals, e.g. one trout eating one or more In summary, experimental studies have the galaxiids. However, observations involving such potential to provide the most compelling small numbers of individuals highlight the evidence of the impacts of salmonids on native need for replication of experiments or several fauna. Unfortunately, very little of this type of sets of observations of similar events to build research has been undertaken in Australia. up a convincing body of evidence to The most useful and practical techniques for demonstrate that predation, for example, is the demonstrating impacts in the field are causal agent for observed trout/galaxiid introduction experiments conducted either in distribution patterns. stream sections or in cages. Experimental The use of artificial stream channels to stream channels and even basic aquaria are investigate interactions between salmonids and ideal tools for investigating impact native fish or between salmonids and native mechanisms. Studies on salmonid/native macroinvertebrates has great potential. These fauna distribution patterns in nature should studies can be set up either in the field, e.g. be designed to incorporate an analysis of all McIntosh et at. (1992), or in the laboratory, e. possible variables which could contribute to g. Edge et at. (1993), and enable interactive the observed distribution patterns. mechanisms to be investigated under controlled conditions. The literature contains examples of a wide range of flow-through and 4.3 Research Priorities recirculating stream channels, e.g. see Salmonids, mainly brown trout, have been Brocksen et al. (1968), Ringstad (1974), implicated in the demise of ten of the fish Cadwallader (1975b). Fausch and White (1983) species classified as threatened (i.e. those in , McIntosh et al. (1992) and Edge et al. (1993), the endangered, vulnerable, potentially and Warren and Davis (1971) have reviewed threatened and indeterminate conservation the possibilities and constraints of their use. status categories) in the Australian Society Even basic glass aquaria can be used to good for Fish Biology 1992 listing (Table 3). effect, e.g. see Glova (1990), to investigate Of these ten species, five are galaxiids (four of predation and other interactions between which, G. fontanus, G. johnstoni, G. pedderensis salmonids and native fish and and G. tanycephaius occur only in Tasmania), macroinvertebrate, particularly to investigate two are nannopercids (pygmy perches), two are the mechanisms of impact of salmonids on the percichthyids (trout cod and Macquarie perch), fauna of lentic waters. and one is a prototroctid (Australian grayling). The most difficult area in which to investigate Macquarie perch and trout cod are relatively the impact of salmonids is that of fish disease, large fish compared with the other threatened primarily because most of the damage in species, and habitat degradation is thought to spreading pathogens has probably already been have played a major part in their demise ( done and because other species, in addition to Cadwallader and Backhouse 1983, Douglas et salmonids, may also be involved in the spread al. 1994). Faragher et al. (1993) suggested that of particular disease organisms. In addition, both brown trout and rainbow trout were likely working with pathogens, particularly viruses, to be major predators of juvenile trout cod. The requires quarantine facilities. However, it effect of trout on these would be of percichthyids still requires clarification, but Table 3. Species in the Australian Society for Fish priority should be given to research on the Biology 1992 listing of threatened fish in whose demise trout, mainly brown trout, have been threatened galaxiids, for which the impact of implicated (after Jackson et al. 1993). trout is thought to be the primary threatening process (Jackson et al. 1993), the pygmy perches for which we have little information on Endangered what caused their demise, and the Australian Galaxias fontanus Swan galaxias grayling. The role of salmonids, particularly Galaxias fuscus Galaxias Barred galaxias trout, in the extinction of the closely-related johnstoni Galaxias pedderensis Clarence galaxias New Zealand grayling Prototroctes oxyrhynchus Maccullochella macquariensis Pedder galaxias still has not been satisfactorily explained, Vulnerable Trout cod although it has been discussed at length ( Galaxias tanycephalus Thomson 1922; Phillipps 1940; Allen 1949, Nannoperca variegate Saddled galaxias 1961; Waugh 1973; McDowall 1968, 1976, Variegated pygmy 1987, 1990a, c). It is, therefore, imperative that perch the impact of trout on the Australian grayling Potentially threatened is investigated. As pointed out by Jackson and Edelia obscura Koehn (1988), it would be unwise to Yarra pygmy perch Prototroctes maraena contemplate stocking trout in waters Australian grayling containing Australian grayling until the Indeterminate relationships between this species and Macquaria australasica Macquarie perch introduced salmonids are better understood. The effects of salmonids on fish in the families Petromyzontidae (particularly 4.4 Management Actions juvenile lampreys), Anguillidae (particularly The most threatened species in whose demise juvenile eels), Aplochitonidae, Retropinnidae salmonids are implicated are the three and Gadopsidae also requires investigation. Tasmanian galaxiids, G. peddererensis, G. There is a pressing need to clarify the impact of fontanus and G, johnstoni, and the Victorian salmonids on the large Tasmanian crayfish galaxiid, G. fuscus. Galaxias pedderensis Anaspides tasmaniae, for which concern over appears to be the species most at risk ( the impact of brown trout has been expressed ( although Galaxias brevipinnis, as well as trout, Williams 1965, 1969; Knott 1973, Knott et al. is implicated in its demise). 1978), and to investigate the impact of Recovery plans, including estimated costs, for salmonids on other freshwater crayfish species, these and the other species of threatened fish including Euastacus spp., Cherax spp. and listed in Table 3 are outlined by Wager and Geocherax spp., which occur in areas occupied Jackson (1993). by trout. In Tasmania, management actions as part of The impact of trout on macroinvertebrates and recovery plans are being implemented for G. aquatic vertebrates other than fish has been pedderensis, Gs fontanus and G, johnstoni, as largely ignored and requires urgent well as for G. tanycephalus (Sanger and Fulton assessment. It is likely that trout have had a 1991, Gaffney et al. 1992, Hamr 1992, Sanger substantial impact on the structure of faunal 1993). The protection of existing populations of communities in fresh waters throughout the G. pedderensis by invasion from brown trout cooler parts of Australia, but this issue, with and Galaxias brevipinnis was considered to be the exception of Morrissy's (1967) study, has both difficult and likely to be unsuccessful, so also largely been ignored. specimens of G. pedderensis were translocated to another lake which had a rich (but not locally endemic) invertebrate fauna (Gaffney et al. 1992, Hamr 1992). However, this translocation of galaxiids to a previously fish- less lake has been criticised as inappropriate on ecological grounds (Horwitz 1995). The recovery plan for G. fontanus involves translocations of fish into upstream sections of streams devoid of brown trout and the

46 augmentation of a small natural barrier to trout access to the galaxiid populations, and to the upstream movement of trout on one assess whether the G. fuscus populations will stream (Sanger 1993). increase following trout eradication. Weirs will Habitat protection measures and translocations be built at the downstream end of the sections to suitable streams and lakes devoid of brown of stream to be secured for G. fiscus and trout are advocated for the conservation of G. trout will be eradicated upstream of the johnstoni. An interesting and practical solution barriers. Two barriers will be constructed at to the problem of preventing the introduction of each site, with the zone between them being brown trout into Clarence Lagoon is to continue monitored for the presence of trout. The stocking the lagoon with brook trout to provide galaxiids upstream of the barriers will be fishing for the many recreational anglers who monitored to record changes in population use the water, thereby reducing the risk of the structure. illegal introduction of brown trout. Brook trout Specific management actions for the protection and Gi johnstoni appear able to coexist. of other fauna thought to be affected by Proposals to safeguard G. tanycephalus include salmonids cannot be undertaken until the a cessation of brown trout stocking in Woods nature and extent of the impacts are lake, one of the only two waters in which this understood. However, as high-level predators, it is galaxiid occurs (Sanger and Fulton (1991). likely that salmonids, particularly brown trout Sanger and Fulton (1991) pointed out that the and rainbow trout, have had a marked impact speed with which the decline in abundance of on aquatic fauna and the structure of aquatic G. pedderensis occurred highlighted the need communities throughout the cooler parts of for routine fish survey work in order to Australia, so that fisheries and conservation recognise declines before they become agencies should ensure that waters or irreversible. They considered that the other six catchments are set aside specifically for the species of endemic galaxiids in Tasmania could maintenance of natural communities and that undergo similar declines at any time and trout are excluded from these areas. In some recommended that refuge populations of all instances it may be necessary to remove Tasmanian galaxiids be established, where the salmonids from particular waters as is being impact from brown trout predation is absent. done in the G. fuscus recovery program in In Victoria, a recovery plan for Galaxias fuscus Victoria (Raadik 1993). The setting aside of is being implemented (Raadik 1993). Part of the such waters or catchments can be program includes the building of trout accommodated in strategic plans for the exclusion structures on two streams to management of inland fisheries and aquatic determine their effectiveness in preventing resources in all affected States and Territories ( section 5.9).

5. POLICIES AND REGULATIONS RELATING TO THE STOCKING AND TRANSLOCATION OF SALMONIDS IN AUSTRALIA

5.1 Introductory Comments alternative arrangements" refer to formal, usually long-standing, arrangements for the Since their introduction into Australia last stocking of trout in particular waters by century, salmonids, particularly trout, have bodies such as the Ballarat Fish been released into most waters thought to be Acclimatisation Society. "Special management suitable for them and have now established or research needs" are those needs which in self-sustaining populations in many of these the view of the Fisheries Branch are sufficient waters, particularly in Tasmania and the cooler to merit variation in general policy for the parts of Victoria and New South Wales (section overall benefit of angling in the State. A 2). Consequently, a great deal of the damage recent example is the stocking of trout eggs has probably already been done as far as via Whitlock-Vibert boxes in a small number impacts on the native fauna is concerned. This of streams by members of angling bodies. of course took place long before codes of The policy states that waters will be practice (e.g. Turner 1988) and issues such as considered for stocking with trout when all of the maintenance of biodiversity (e.g. Kitching the following conditions are satisfied: and Lyonns 1993) were regarded as being • sufficient acceptable or marginal habitat important. However, a review of the current for their maintenance and/or growth policies, regulations and guidelines of the exists; various State and Territory agencies on • natural reproduction is insufficient to salmonid stocking and translocation in relation support a fishery; to impact on native fauna reveals a wide range • the fish are accessible to anglers; and of attitudes and responses to the problem. • there is a reasonable expectation that enough anglers will fish the water to justify 5.2 Victoria the expenses involved. The Department of Conservation and Natural Priorities for waters considered for stocking Resources, specifically the Fisheries Branch, is are determined by habitat suitability criteria, the agency responsible for salmonid stocking in existing or potential trout population levels Victoria. The Department considers trout to be and the needs of the angling public. "desirable introduced species" and manages The policy states that stocking of trout will the State's recreational fishery on that basis. not occur in waters in the following The Department also supports the commercial categories: aquaculture of salmonids. • where the released fish may constitute a The current policy on stocking trout in public threat to a population of a species of waters has been in place since 1988. The policy special concern or where an unique faunal states that the Department will produce trout assemblage occurs; for stocking inland waters and that stocking • where natural reproduction adequately will be confined to public waters except where supports a fishery; recognised alternative arrangements exist or • waters east of the Snowy River catchment; special management or research needs exist or and arise. "Recognised • waters identified as unacceptable habitat.

49 The Victorian Fisheries Act 1968 requires that out what has been done to conserve and all persons wishing to release fish into manage a taxon, a community or, potentially Victorian waters must first have written threatening process and what is intended to permission from the Department of be done. Action statements become public Conservation and Natural Resources (a documents. standard application form is provided for this Two examples of relevant nominations for purpose). Further, a person is required to listing under the Flora and Fauna Guarantee notify the Department if bringing fish or fish Act are given below. eggs from interstate. Trout releases are not The "deliberate or accidental introduction of permitted in private waters in the Mallacoota live fish into public or private waters within a basin in east Gippsland; few introduced fish Victorian river catchment in which the taxon to occur in this area, which is managed by the which the fish belongs cannot reliably be Department of Conservation and Natural inferred to have been present prior to the year Resources for the protection of its natural 1770 AD" was recommended by the Scientific aquatic fauna. Advisory Committee on 10 March 1992 for The Victorian Flora and Fauna Guarantee Act listing as a potentially threatening process on was proclaimed in Victoria in 1988. The Schedule 3 of the Flora and Fauna Guarantee Department of Conservation of Natural Act 1988. Resources, specifically the Flora and Fauna "Galaxias olidus var. fuscus - Tiger or Brown Branch, is responsible for the administration Galaxiid" was recommended by the Scientific of the Act. Advisory Committee on 22 May 1991 for The relevant objectives of the Act are: listing as a threatened taxon on Schedule 2 of • to guarantee that all taxa of Victoria's flora the Flora and Fauna Guarantee Act 1988. and fauna can survive, flourish and retain The impact of trout was recognised as a threat their potential for evolutionary which was likely to lead to the extinction of development in the wild; the taxon. • to conserve Victoria's communities of flora and fauna; • to manage potentially threatening 5.3 New South Wales processes; New South Wales Fisheries is the agency • to ensure that any use of flora and fauna responsible for salmonid stocking. Trout are by humans is sustainable; considered "beneficial" and are stocked on a • to ensure that the genetic diversity of flora regular basis. The commercial aquaculture of and fauna is maintained; salmonids is supported. • to provide programs of community The New South Wales Fisheries and Oyster education in the conservation of flora and Farms Act 1935 prohibits the stocking of fish, fauna; and or the eggs or fry of any fish, into any waters • to encourage the conserving of flora and without the consent of the Minister. fauna through co-operative community The objectives of stocking salmonids are: endeavours. • to maintain adequate stocks in public Any person or organisation can nominate waters by stocking streams and threatened taxa and communities or impoundments in which there is potentially threatening processes for listing inadequate natural reproduction or in under the Flora and Fauna Guarantee Act. An which environmental factors have had a independent Scientific Advisory Committee deleterious effect on stocks; and assesses the validity of the nominations and • to ensure that all fish stocked in public makes recommendations for listing either on waters are free of specified diseases. Schedule 2 of the Act (threatened taxa or The number of each species produced is communities) or Schedule 3 of the Act ( determined in consultation with recreational potentially threatening processes). Once a fishers. threatened taxon or community or a The principles governing stocking include: potentially threatening process is listed, the • all proposed stockings of public waters Department of Conservation and Natural must be approved by NSW Fisheries before Resources must prepare an action statement the stocking takes place; as soon as possible. An action statement sets

50 • all stockings of salmonids into public 5.5 Tasmania waters, regardless of the source of the stock, must be reported immediately to The Inland Fisheries Commission is NSW Fisheries on stocking data forms; responsible for salmonid stocking in the • all salmonids stocked into public waters inland waters of Tasmania. must be from hatcheries which are In its April 1987 newsletter, it was reported certified free from EHN virus, goldfish ulcer that the Inland Fisheries Commission had disease, yersiniosis and any other disease adjusted its trout stocking policy "to avoid stipulated by NSW Fisheries; conflict with sensitive native species". As a • in general, salmonids should not be stocked general policy, salmonids are only stocked in in areas where they have not previously waters in which they already occur. This has been stocked; been the case for some years. A general rule is • in general, salmonids should not be stocked that trout stocking also does not occur in into areas where they could compete with National Parks, although present trout stocks populations of endangered species; in parks are self-sustaining. • salmonids supplied to acclimatisation In specific areas such as Clarence lagoon societies must be stocked into public where Galaxias johnstoni occurs, the waters which have open access; and development of a recreational fishery based salmonids should not be stocked into on stocking with brook trout rather than streams to which they are not biologically brown trout is encouraged because brook suited and in which lethal or sub-lethal trout and G. johnstoni appear to be temperatures have regularly been compatible, unlike brown trout and G. experienced in the past. johnstoni (W. Fulton, Inland Fisheries Commission, Tasmania - pers. comm.).

5.4 Australian Capital 5.6 South Australia Territory The Department of Primary Industries, The ACT Parks and Conservation Service is the specifically the Fisheries Branch, is the agency responsible for salmonid stocking. agency responsible for salmonid stocking in Current policy is that there is no stocking of South Australia. salmonids (or native species) in streams in the The introduction and control of all non-native ACT, but trout are stocked for recreational fish is covered by the Fisheries (Exotic Fish, fishing purposes in Canberra's urban lakes. In Fish Farming and Fish Diseases) Regulations, practice, there has been little stocking of 1984. This legislation prohibits the importation salmonids in these lakes because of poor of all non-native fish to South Australia, but survival rates. allows the Department of Primary Industries to Salmonids are not stocked in the three Cotter issue permits allowing the importation and River water storages, viz. Corin, Bendora and farming of exotic fish if it is satisfied that the Cotter Reservoirs, because all three are closed fish are certified diseasefree and that they will to fishing. Furthermore, Cotter and Bendora be stocked or farmed in a manner consistent Reservoirs are in the Namadgi National Park with the aim of the Fisheries Act 1982 to and, together with their feeder streams, are conserve and enhance fish stocks in South managed as a "fish conservation zone", with Australia. the reduction of existing trout populations as a Under permit, the South Australian Fly management aim. Fishers' Association is the body which Googong Reservoir is managed jointly by the undertakes the importation and stocking of ACT Parks and Conservation Service and NSW salmonids, mainly brown trout and rainbow Fisheries. Trout are currently stocked in an trout. Eyed eggs are obtained usually from attempt to enhance the recreational fishery (M. Tasmania, hatched and the young trout are Lintermans, Parks and Conservation Service, either stocked into public waters or sold for ACT Department of the Environment, Land and stocking private waters (farm dams), usually Planning - pers. comm.). in the Adelaide Hills area. In the past, the Fly Fishers' Association in Queensland is currently being developed, attempted to stock any water which would which incorporates both decision making support trout through a normal season. Any protocols and disease risk assessment stretch of water which held trout for four out protocols (P. D. Jackson, Department of of five years was considered worth stocking (J. Primary Industries, Queensland - pers. Williams, South Australian Fly Fishers' comm.). Association - pers. comm.). The public waters which can now be stocked by the Fly Fishers' Association are limited by the Department of 5.9 Future Directions Primary Industries to about 5-6 rivers so as to Historically, in Australia the value of avoid potential conflict with threatened native salmonids as sport-fish and, later, as fauna. aquaculture species has overshadowed consideration of their effects on native fauna and, in general, legislation to safeguard native 5.7 Western Australia fauna from the impacts of salmonids has been The Fisheries Department is the agency lacking. Given the more enlightened public responsible for stocking salmonids. It has attitudes of recent years and the adoption by, recently released a discussion paper on the fisheries management agencies of the principles issues relating to the introduction of fish, of ecologically sustainable development, crustaceans and molluscs in Western incorporating the maintenance of biodiversity, Australia (Lawrence 1993). it is time for the various agencies responsible In relation to brown trout and rainbow trout, for salmonid management to re-assess their it is recognised that the cost of their attitudes towards the- adverse impacts of introduction into Western Australia is their salmonids and to take a more pro-active impact on natural ecosystems. On the other approach to protecting native fauna. hand, the benefits arising from their It is not good enough to say that no new introduction are the establishment of a waters will be stocked with salmonids when recreational fishing industry and an every inland fisheries manager in Australia aquaculture industry. It is seen as a benefit knows that almost every water which was that trout are unable to establish-self- thought to have been suitable for the survival sustaining populations in many waters, despite of salmonids has already been stocked with having been stocked for over 90 years. In order them! What is required is a more positive - to preserve "the integrity of existing trout approach in setting aside waters or populations" it is recommended that any catchments specifically for the management of further importation of trout into Western native fauna and: from which salmonidsare Australia should continue to be discouraged in excluded and, if necessary, removed. The order to minimise the risk of introducing Victorian Flora and :Fauna Guarantee Act 1988 pathogens. Although trout are released to is a good model for providing the legislative enhance the recreational fishery in specific framework for such an approach. The areas of the south-west of the State, stocking approach is not one of trying to turn back the is not now widespread because of conservation clock to a time when there were no salmonids concerns. in Australia, but to recognise that as well as The introduction of aquatic species for the providing substantial recreational and aquaculture industry is strictly controlled. All economic benefits, salmonids do have an interstate translocations of aquatic organisms adverse impact on Australia's aquatic fauna for aquaculture purposes currently require and that this fauna must be protected. health certification to prevent the introduction Currently, this protection is most needed in of disease. Tasmania. Within a strategic framework for the management of fisheries and-aquatic fauna, it 5.8 Queensland is possible to accommodate salmonid fisheries Salmonids are not a significant component of as well as the conservation of native fauna. For the Queensland fish fauna and their impact in example, recognising the need to balance the that State is negligible. However, it is worth various demands being made on the aquatic mentioning that a comprehensive policy for the environment and the resources it translocation of freshwater fish supports and at the same time ensuring that all such demands are ecologically sustainable, a proposal has been developed for a Victoria- wide strategic plan to accommodate the conflicting demands of conservation, recreational fishing and aquaculture ( Cadwallader 1992). Within the strategic framework, it is proposed that some water bodies or catchments would be managed primarily for the protection or rehabilitation of threatened fish species and other aquatic organisms and for the maintenance of aquatic habitats and their communities in a natural or undisturbed state. Other water bodies or catchments would be managed primarily for recreational fishing in its various forms, and yet others would be managed for commercial fishing, including aquaculture. There is a need for such an approach to be adopted more widely in order to ensure the survival of native fauna at the same time as enabling the continuation of the enjoyment of salmonids as fine sport-fish.

6. CONCLUSIONS AND RECOMMENDATIONS

1. There have been few studies on the impacts 6. Studies on the interactions between juvenile of salmonids on fauna other than fish and, salmonids and native fauna indicate that considering the families of fish which occur direct competitive encounters may occur in areas in which trout have been between juvenile salmonids and those introduced in Australia, including estuarine species which occupy the same microhabitat as well as freshwater habitats, the studies and feed in the same manner on, the same cover a relatively small part of the native foods. Conversely, those native species fish fauna. which, because of their particular life 2. The most substantive evidence of impacts of histories and habitat requirements are able salmonids in Australia comes from Fletcher' to avoid direct encounters are likely to be s (1979) experimental introduction study able to co-exist with salmonids. and from observations such as those of 7. The impact of salmonids on native fauna Tilzey (1976), Raadik (1993) and Closs and via the spread of pathogens, particularly via Lake (in prep) during the invasion of trout the widespread releases of hatchery- into new areas. produced fish, is unknown. However, the 3. With few exceptions, much of the occurrence of pathogens in salmonid information on the distribution of hatchery stocks indicates that salmonids salmonids and native fish is derived from have undoubtedly played a major role in general fish surveys not specifically the spread of these disease organisms, designed to investigate the effects of irrespective of whether or not the salmonids on particular species or aquatic pathogens were introduced into Australia communities. with the salmonids. 4. Taken together, the numerous and 8. Future studies of the distributions of widespread instances of fragmented galaxiid salmonids and native species in Australia distribution patterns in the presence of should adopt the approach taken by trout, the more widespread distribution of Townsend and Crowl (1991). Their statistical these galaxiids in the absence of trout, and analyses incorporating various physical, the observations of fragmentation of the chemical and biological variables from a galaxiid distribution pattern as trout large number of sampling sites indicated progressively move upstream, provides a that the presence and abundance of a substantial body of evidence for an adverse particular species were best predicted by the impact of trout on these stream-dwelling presence or absence of trout rather than by galaxiids. any of a wide range of other possible 5. Studies on the mechanisms by which variables. Their study was specifically salmonids have had an impact on the designed to test the hypothesis that the native fauna are sparse, but nevertheless occurrence of a particular native species indicate that predation has been the major was affected by the presence of brown trout. cause of the impact. This sort of approach is much more useful than merely recording the absence of native species in the presence of salmonids because it provides information on the likely cause of the observed distribution patterns of the native species which presence/ absence studies do not provide. 9. Introduction experiments in the field 14. Salmonids, -mainly brown trout, are . provide the most convincing evidence of implicated in the demise of ten of the fish an impact of salmonids on native fish. species classified as threatened by the 10.Introduction experiments in nature imply Australian Society for Fish Biology. Of these setting up the experiment in an area in species, five are galaxiids, two are which trout have not previously occurred. In nannopercids (pygmy perches), two are situations where evidence of impact is being percichthyids (trout cod and Macquarie sought for threatened species it may be perch), and one is a prototroctid (Australian inappropriate to introduce trout into an area grayling). The effect of trout on the which they had not previously occupied. In percichthyids still requires clarification, but such circumstances, one approach would be priority should be given to research on the to monitor the aquatic community in a threatened galaxiids, for which the impact stretch of stream in which trout occur, then of trout is thought to be the-primary remove the trout downstream to a natural threatening process, the pygmy perches for or artificial barrier and monitor the which there is little information on what subsequent changes in the aquatic caused their demise, and the Australian community. grayling. 11.Data from Renowden's (1968) study on 15.The impact of trout on macroinvertebrates the distribution of galaxiids and trout in and aquatic vertebrates other than fish has pools in a small stream indicate the been largely ignored and requires urgent relatively small numbers of fish likely to be assessment. It is likely that introduced trout encountered in field studies of the impact of have had a substantial impact on the salmonids on native fauna. Such small structure of faunal communities in fresh numbers do not detract from the value of waters, throughout the cooler parts of the observations because, at the field level, Australia. elimination of one species by another 16. In Tasmania, recovery plans are being ultimately involves interactions between implemented for Galaxias pedderensis, G. individuals. However, observations involving fontanus, G, johnstoni, and G. such small numbers of individuals highlight tanycephalus. The speed with which the the need for replication of experiments or decline in abundance of G. pedderensis several sets of observations of similar events occurred highlights the need for routine to build up a convincing body of evidence. fish survey work in order to recognise 12.The use of artificial stream channels to declines before they become irreversible. investigate interactions between salmonids 17.It is recommended that reserves for all and native fish or between salmonids and Tasmanian galaxiids be established. native macroinvertebrates has great 18.In Victoria, a recovery plan for Galaxias potential. fuscus is being implemented. The program 13.The most difficult area in which to involves the building of trout exclusion investigate the impact of salmonids is that structures to determine their effectiveness of fish disease, primarily because most of in preventing trout access to galaxiid the damage in spreading pathogens has populations and to assess whether the G. probably already been done and because fuscus populations will increase following other species, in addition to salmonids, may trout eradication. also be involved in the spread of particular 19.The value of salmonids as sport-fish and disease organisms. as aquaculture species in Australia has overshadowed consideration of their effects on native fauna and, in general, legislation to safeguard native fauna from the impacts of salmonids has been - lacking.

56 20. It is recommended that the various 22.Within a strategic framework for the agencies responsible for salmonid management of fisheries and aquatic management re-assess their attitudes fauna, it is possible to accommodate towards the adverse impacts of salmonids salmonid fisheries as well as provide for and take a more pro-active approach to the conservation of native fauna. There is a protecting native fauna. need for such an approach to be adopted 21. It is recommended that waters or more widely in Australia. catchments be set aside specifically for the management of native fauna and from which salmonids are excluded or, if necessary, removed. The Victorian Flora and Fauna Guarantee Act 1988 is a good model for providing the legislative framework for such an approach. The approach is not one of trying to turn back the clock to a time when there were no salmonids in Australia, but to recognise that as well as providing substantial recreational and economic benefits, salmonids have an adverse impact on Australia's aquatic fauna and that this fauna must be protected. Currently, this protection is most needed in Tasmania.

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