Fisheries

Introduction

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The variety of fish found in the rivers of the Murray-Darling Basin is extremely small, with no more than 50 species having been so far recorded. Of these, 11 are introduced species, several are essentially marine or estuarine species found only in the lowest reaches of the Murray, and 6 are diadromous, spending part of their life cycles in freshwater and part in the sea. Only 26 native species complete their life cycles totally within the Murray-Darling river system. Much remains to be learned about the the native fish of the Basin. For example, it was only in the 1970s that the Murray cod and trout cod were recognised as separate species, while as recently as 1991, a new species of yabbie was identified in the Barmah Forest.

The fish species present in the Murray-Darling Basin are listed in Table 1, with the diagram and map (Figure 1) providing a general indication of their distribution.

Figure 1  Freshwater fish by ecozones within the MDB (source MDBMC 1987)

Fish numbers and their changes in the MDB

The Murray-Darling river system has always been an unpredictable environment, ranging from severe floods to droughts, resulting in large fluctuations in fish populations. However, over the period of European settlement, there have been dramatic declines in both the numbers and distribution of most native species. For example, in the early years, there was an important commercial fishery (see below). More recently, over the 50 years to 1992, studies at Euston Weir on the River Murray indicated a 94 per cent decline in silver perch numbers and a 74 per cent decline in golden perch. Similar declines in silver perch populations in other rivers have also been observed.

Many species, such as the silver perch, western chanda perch and purple-spotted gudgeon, are said to be 'restricted', being now found only in limited areas. A number, such as the trout cod and Macquarie perch, are so reduced in numbers and distribution that they are now regarded as 'endangered', that is, they are in danger of extinction, and they are totally protected. There are only two natural breeding populations of the trout cod, in the River Murray between Yarrawonga and Tocumwal, and Seven Creeks in Victoria. The largest remaining population of silver perch is between Torrumbarry and Euston and its conservation is a high priority. Many other species, such as the southern pygmy perch and flat-headed galaxias, have also suffered dramatic declines in range and abundance. However, the full situation with regard to the Basin's fish population is essentially unknown (Cadwallader & Lawrence 1990); Kailola et al. 1993).

The Murray cod is the largest freshwater fish found in Australia and regarded as the Basin's premier species. It also occupies a special place in the Basin's history and folklore (Cadwallader 1993). The significant decline in its numbers over the past forty years has given rise to considerable research to arrest the decline and endeavours to re-establish larger populations.

Some reasons for changes in fish populations

Various factors have contributed to the decline in native fish numbers over the period of European settlement (Lawrence 1989; NSWWRC 1993; Gehrke et al. 1995).

River regulation

The regulation of almost all of the Basin's rivers to provide water for irrigation and other purposes has been to detriment of the native fish populations. Total flows have been reduced; the seasonal flow patterns have been changed; water levels in rivers change much more quickly than under natural conditions; and flood frequencies - especially the small and medium-sized floods - have been greatly reduced with the construction of reservoirs and other storage structures.

The reduced frequency of flooding is of particular significance, as it is the high flows that cause the migratory fish to move upstream to spawn, whilst it is the floodplains and wetlands that provide feeding, spawning and nursery areas for many species, such as Murray cod and silver perch. Most native fish spawn in spring, requiring particular water level and temperature conditions. Cold water releases from reservoirs that occur during periods of fish migration and spawning reduce spawning opportunities and survival rates. Rapid fluctuations in river levels are also deleterious for fish that spawn in shallow water, leaving fish or their eggs or fry stranded.

Barriers to fish movement

Many fish use different parts of a river system at different stages in their life cycles. For some species, such as the gudgeons and smelt, these can all be within a relatively short stretch of river, but for others, the distances involved can be considerable. For example, the golden perch spawns in flooded reaches of lowland rivers, the young use the floodplains as nurseries, and later they move upstream. The golden and silver perch move over most of the Murray-Darling river system, with the Murray cod covering recorded distances of 1,000 km and the golden perch 2,300 km (Figure 2).

Figure 2 Movement of golden perch and barriers to fish movement in the MDB (source: Reynolds 1983; Lawrence 1989, 130)

Movement over such distances is now only possible during periods of major floods, as numerous barriers to fish movements have been erected across virtually all of the Basin's rivers (Figure 2). Combined with the regulation of the rivers, these barriers have had major impacts on the life cycles of many fish species, especially the migratory ones, contributing to reductions in their numbers and distributions. For example, golden and silver perch disappeared between Yarrawonga Weir and Hume Dam following their construction. Approximately 2,900 barriers have been documented across the Basin.

Fishways of different kinds exist on 22 of the barriers, but most are poorly designed and offer only limited fish passage. To help overcome the problems created by such barriers, changes are being made to the operation of the Murray mouth barrages (in the interest of the fish populations of the Coorong) and the locks on the lower reaches of the Murray (to facilitate and encourage fish migration upstream). At other barrages, new fishways have been constructed, as at Torrumbarry (as part of the new weir) and Yarrawonga, with new facilities planned for
other locations.

Decline of water quality

Over the period of European settlement, many factors have contributed to the decline of water quality in the Murray-Darling Basin (see Water Quality), to the significant detriment of the fish population. Some of the pollutants affect the fish directly, others indirectly through damage done to their habitats. They include siltation of waterways, suspended sediment (which can clog the gills of fish), increasing salinity levels, agricultural chemicals, and effluent from industries and sewage treatment works. Some chemicals, such as endosulfin, are directly toxic to fish and other marine organisms, but much less is known about the sub-lethal effects of chemicals and other pollutants.

Excessive quantities of nutrients, especially nitrogen and phosphorous, not only contribute to the growth of algae, some of which are toxic, but also result in depletion of dissolved oxygen in the water, to the obvious detriment of fish and other marine organisms (see Water Quality).

River improvement

The many features of a river channel and its banks, such as weed beds and other plants, rocks, logs, and different types of stream beds, provide the essential habitats for fish, for shelter, resting areas, spawning sites and food sources. Greater diversity of environments contributes to greater biological productivity. However, in the name of 'river improvement', much has been done over the years that has reduced and even eliminated the diversity, through the removal of snags and river-side vegetation and the realignment or reconstruction of river banks. Such measures have been to the detriment of fish habitats and populations.

Overfishing

The overall declines in fish numbers and distributions, as well as the natural fluctuations, make it difficult to determine the real effects of overfishing. It appears much less of a problem than the changes to the natural habitat. However, given the limited knowledge of many species and their scattered distributions, even very limited fishing can be excessive for a 'restricted' or 'endangered' species, such as the silver perch and trout cod.

It is for such reasons that the state fisheries authorities place various restrictions on what can be caught in terms of numbers and species and on the fishing gear that can be used. At particular times and places, there are bans on fishing, such as the closed season for Murray cod and protection for trout cod in the River Murray downstream of Yarrawonga Weir (Table 2)

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Exotic species and diseases

The impacts of the introduced species on the native fish and aquatic habitats of the Basin are still inadequately known and, as a consequence, are matters of controversy. Clearly, there is competition for food, such as between the Murray cod and redfin at the larval and juvenile stages. Reservoirs have provided ideal environments for some exotic species, such as carp, while the maintenance of constant water levels behind weirs and in wetlands has benefited exotic species to the detriment of native ones.

There is growing evidence of the detrimental impact of European carp (Cyprinus carpio) on native species of fish and the overall aquatic environment (MCMC 1994; Anon. 1995; Brown 1996). In no more than 30 years after their illegal release into Lake Hawthorn, near Mildura, carp are now estimated to account for from 70 to over 90 per cent of fish numbers in the rivers of Murray-Darling Basin (The Australian, January 13, 1996). Because of their feeding methods, carp are undermining the banks of rivers, killing aquatic plants, and stirring up bottom sediments, releasing nutrients that contribute to blue-green algae outbreaks, as well as killing and feeding on the organisms that graze on the blue-green algae (Gehrke & Harris 1994). They are also interbreeding with goldfish. Carp have been described as the rabbits of the waterways. In a South Australian wetland where carp have been eliminated, there have been significant improvements in aquatic plants, water quality and bird life. The National Carp Task Force is providing a focus for continuing research and community concern relating to carp (see its newsletter, Cyprinus).

With the introduction of exotic species have come a number of pathogens and diseases that affect native fish, for example, epizootic haematopoietic necrosis (EHN) virus was introduced with redfin into areas of New South Wales and Victoria. Thus far it has affected only redfin, but it could spread to native species. There is also concern about a virus associated with barramundi farming to which native species have shown susceptibility. Other viruses are associated with specific species: for example, spring viraemia is believed to be specific to carp and offers a potential means of control option.

Managing the fish resources of the MDB

As part of the endeavours to restore the Basin’s fisheries, and especially the status of the native species, the Murray-Darling Basin Commission in 1991 approved a Fish Management Plan for the Basin to complement the activities of the state fisheries authorities (MDBC 1991). this was completely revised , and updated and re-issed as the Native Fish Strategy 2003-2013. 

Fishing in the Murray-Darling Basin

Long before European settlement, native fish species provided an important source of food for Aboriginal people. Large quantities were harvested and some of the fish traps they used are still to be seen along the Darling River (see Heritage Resources). Large quantities were also harvested in the early to mid-19th century by European settlers, but there was a rapid decline in the catch through the latter part of the last and the early years of this century.

Fishing in the Murray-Darling Basin has long been both commercial and recreational.

Commercial fishing

The Murray-Darling Basin is the only area in Australia where commercial freshwater fishing is undertaken. The waterways involved are much more restricted than previously, with the main ones being the Coorong, Lakes Alexandrina and Albert, Lake Victoria, the Lower Darling, the Murray and Murrumbidgee, and the Edward and Wakool Rivers. On a state basis, commercial fishing is virtually limited to New South Wales and South Australia (Stewart et al. 1991).

The main species fished commercially are the Murray cod, golden perch, freshwater catfish, European carp, and bony bream. In South Australia, the main species in quantitative terms are the golden perch (callop), European carp and bony bream; in New South Wales, they are the European carp, golden perch, Murray cod and redfin. Annual catches vary considerably, as illustrated by data for New South Wales (Figure 3).

Figure 3 Total catch of inland commercial fisheries in New South Wales, 1947-84 (source: Derwent 1984)

The most important fish for human consumption (and the most important in economic terms) is the golden perch (callop), with annual catches in South Australia ranging from 50,000 to 175,000 kg, and, in New South Wales, from 80,000 to 240,000 kg (Rohan 1989). The second most important fish taken for human consumption is the Murray cod, the prime table fish and one of the world's largest freshwater species. "Recent catches in South Australia have ranged from 3,500 to 20,000 kg per annum and, in New South Wales, from 10,000 to 28,000 kg per annum. In the 1950s, catches in the order of 100,000 kg per annum were still taken in South Australia" (Cadwallader and Lawrence 1990). Bony bream is used for pet food, crayfish bait and fishmeal. One means of assisting the control of carp would be an expansion of the commercial fishery, not only for human consumption but more especially for the production of fishmeal (most of which is currently imported) and other products (MCMC 1994; Roberts & Tilzey 1997). In South Australia, efforts are being made to expand the human consumption of carp, while carp are being used for the production of stockfeed pellets (at Curlwaa) and liquid fertiliser (at Deniliquin).

Commercial fishing data for 1990-91 are shown in Table 3. With the exception of carp, the commercial fishery in the Basin is a declining industry, due in part at least to the reduced numbers of fishermen.

In addition to river fishing, there is now an important commercial fish farming or aquaculture industry in the Basin, with an increasing number of operations, particularly to supply fresh fish to local markets (see for example Carson 1995) (Figure 4).

Figure 4 Fish farms and hatcheries and fishways on rivers in MDB

There are over 60 licensed fish farms in the Basin. The most important species farmed is the rainbow trout, with production of over 320 tonnes per annum valued at $1.6 million. Other species produced include Murray cod, Atlantic salmon, golden perch, brook trout, and catfish (GHD 1992, 8-7/8). As with other intensive livestock operations, there is growing concern about the high nutrient levels of effluent.

Yabbies are also caught commercially in South Australia and New South Wales, but have suffered from loss of habitat and overfishing. In the early 1970s, annual catches over 100,000 kg were recorded in Lake Alexandrina. Yabbies are also produced on a number of fish farms in New South Wales.

Recreational fishing

Recreational fishing is the third most popular outdoor activity in Australia (Ross & Duffy 1995). In the Murray-Darling Basin, it is of far more importance than the commercial fishing industry. It is undertaken in virtually all of the Basin's rivers and reservoirs and forms a major part of the Basin's recreational and tourism activities (Lynch 1995). No clear data are available on the catch taken by recreational fishing, but the activity has an economic value estimated at over $400 million a year. At least 1.75 million people fish recreationally in New South Wales each year.

The main species fished in the Basin are the Murray cod (the most sought after fish), golden perch, silver perch, freshwater catfish, spangled perch, river blackfish, two-spined blackfish, brown and rainbow trout, and Atlantics salmon. The yabbie and River Murray crayfish (the world's second largest crayfish, weighing up to 3kg) are also targets for recreational fishing.

Fish breeding and stocking

The Basin's freshwater fisheries are supported by a number of research stations and hatcheries, operated by state government authorities and private interests.

The research stations play an important role in increasing knowledge of the Basin's fish and ensuring the continued existence of the restricted and endangered species. The major centres are the Inland Fisheries Research Station at Narrandera, Snobs Creek Research Centre at Eildon, and Kaiela Fisheries Research Station at Shepparton.

The major function of the hatcheries is to breed young fish or fingerlings for release into the Basin's rivers and reservoirs. For example, in 1991-92, over one million juvenile native fish and three million trout and salmon were released into New South Wales waters. In addition, in 1991, 37,000 fry of the endangered trout cod were released. On a smaller scale, the Charleville Fishing and Restocking Club has released over 128,000 golden perch (yellowbelly) fingerlings into the Warrego and other local rivers since 1991.

Conclusion

Australians place a very high value on the country's freshwater fish, especially the native species, a value significantly greater than the economic returns from the commercial and recreational fisheries. In spite of this, fisheries rank low in the order of priorities in terms of the rivers and the use of the water. Yet there is no better indication of river health than the nature of the native fish stocks.

References

Anon. (1995): National Carp Summit Proceedings. Murray Darling Association, Adelaide.

Brown, P. (1996): Carp in Australia. Fishfacts 4. NSW Fisheries, Sydney.

Cadwallader, P. (1993): Ponde, the Murray Cod. Murray-Darling Basin Commission, Canberra.

Cadwallader, P. & Lawrence, B. (1990): "Fish". pp. 317-335 in The Murray, edited by N. McKay & D. Eastburn. Murray-Darling Basin Commission, Canberra.

Carson, J. (1995): "Fish farm leaps into the big time". Australian Farm Journal, 5(8), 22-24.

Derwent, L. (1994): "Commercial and recreational fishing of carp in NSW: current management and options". pp. 43-49 in Proceedings of the Forum on European Carp, Wagga Wagga, NSW 20th June 1994. Murrumbidgee Catchment Management Committee, Wagga Wagga.

Geddes, M. (1990): "Crayfish". pp. 303-307 in The Murray, edited by N. McKay & D. Eastburn. Murray-Darling Basin Commission, Canberra.

Gehrke, P. & Harris, J. (1994): "The role of fish in cyanobacterial blooms in Australia". Australian Journal of Marine and Freshwater Research, 45(6),

Gehrke, P. et al. (1995): "River regulation and fish communities in the Murray-Darling river system, Australia". Regulated Rivers: research and management, 11, 363-375.

GHD (1992): An Investigation of Nutrient Pollution in the Murray-Darling River System. Gutteridge Haskins & Davey for the Murray-Darling Basin Commission, Canberra.

Kailola, P.J. et al. (1993): Australian Fisheries Resources. Bureau of Resource Sciences / Fisheries Research and Development Corporation, Canberra.

Lawrence, B. (Editor)(1989): Proceedings of the Workshop on Native Fish Management, Canberra, June 1988. Murray-Darling Basin Commission, Canberra.

Lynch, P. (1995): Freshwater Guide 1995.:a guide to NSW inland fishing laws. New South Wales Fisheries, Sydney.

MCMC (1994): Proceedings of the Forum on European Carp, Wagga Wagga, NSW 20th June 1994. Murrumbidgee Catchment Management Committee, Wagga Wagga.

MDBC (1991): Fish Management Plan. Murray-Darling Basin Commission, Canberra.

MDBMC (1987): Murray-Darling Basin Environmental Resources Study. Murray-Darling Basin Ministerial Council, Canberra.

NSWWRC (1993): Our Water: a review of the current status of the water resources of New South Wales and the key issues relevant to their future development. NSW Water Resources Council, Sydney.

Pease, B.C. & Scribner, E.A. (1993): New South Wales Commercial Fisheries Statistics 1990-91. NSW Fisheries, Sydney.

Reynolds, L.F. (1983): "Migration patterns of five fish species in the Murray-Darling river system". Australian Journal of Marine and Freshwater Research, 34, 857-871.

Roberts, J. & Tilzey, R. (Editors)(1997): Controlling Carp: exploring the options for Australia. CSIRO Land and Water, Griffith.

Rohan, G. (1989): "River (Murray) fishery review". Safish Magazine, 13(3), 4-7.

Ross, J. & Duffy, H. (Editors)(1995): Fish Australia: the essential fishing companion. Viking-Penguin Books Ltd., Melbourne.

Stewart, P. et al. (1991): Twenty Five Years of Australian Fisheries Statistics. Working Paper WP 14/91. Bureau of Rural Resources, Department of Primary Industries and Energy, Canberra.

Table 1 Fish and crayfish species in the Murray-Darling Basin (source: Cadwallader & Lawrence 1990; Geddes 1990)

* Hybrids between carp and goldfish are quite common.

Table 2 Limits on freshwater fishing in the Murray-Darling Basin (sources: Lynch, P. (1995): Freshwater Guide 1995: Guide to NSW Inland Fishing Laws. NSW Fisheries, Sydney; Anon. (1995): Freshwater Recreational Fishing in New South Wales: A Brief Guide with New Trout Rules. NSW Fisheries, Sydney; Anon. (1995): Recreational Fishing in South Australia. Primary Industries South Australia, Adelaide; Anon. (1995): Victorian Recreational Fishing Guide. Victorian Fisheries Department of Conservation and Natural Resources, Melbourne; Anon. (1996): Recreational Fishing in Queensland Freshwater. Queensland Boating and Fisheries Patrol, Brisbane)

1. Fish are measured from the snout to the tip of the tail, except for Murray crayfish which are measured from the rear of the eye socket to the centre of rear of carapace.

2. The figures for bag limits are for fishing in rivers.  The second figures, with an asterisk, are for fishing in dams.  It should be noted that various restrictions apply to fishing in terms of locations and closed and open seasons.  For these, the individual state regulations should be consulted.

3. There is a closed season in NSW and Victoria on the taking of Murray cod from September 1 to November 30.  In South Australia, the closed season extends from September 1 to December 31.

4. Only in the waters of Lake Hume and Mulwala.

5. No limit on fish over 21cm but under 35cm.

6. 'Usually taken at 750g, 35cm' (Recreational Fishing in Queensland Freshwater).

7. Bag limit for trout and salmon in NSW varies with season and location.

8. (a) in, on or next to lakes and impoundments north of the Great Dividing Range (excluding the Wimmera Basin); and (b) in, on or next to all waters south of the Great Dividing Range (including the Wimmera Basin). (c) Silver Perch must not be taken from any other waters north of the Great Dividing Range.
   
   
9. Freshwater Catfish must not be taken from any other inland waters or marine waters, other than in, on or next to all waters within the Wimmera Basin.
   
   
10. Applies only to Lake Dartmouth and its tributaries, the Yarra River and its tributaries and the Upper Coliban Reservoir and its tributaries. Macquarie Perch must not be taken from any other inland waters or marine waters.
    A closed season on the taking of Macquarie Perch applies from 1 October to 31 December in each year.
11. South Australia.- Crap / Redfin / Mosquito fish - introduced species not to be returned to the water alive.

Note that this is a very general summary, that specific rules and regulations may apply to particular locations, and that the regulations change from time to time.

Table 3 Commercial freshwater fish catches in New South Wales and South Australia,  1990-91 (source: South Australian data provided by South Australia Fisheries; New South Wales data from Pease & Scribner 1993; Stewart et al. 1991)

* The figures are for the whole of New South Wales, but for the species listed, the greater part of the fishing activity and aquaculture is in the Murray-Darling Basin.