If all permanent and seasonal water bodies supported fish to their maximum carrying capacity, there would be plenty to be caught for food and income or for recreation. Total recreational fishery is estimated to be worth over $50 million annually to the State of Victoria alone. Fish are an invaluable source of protein throughout Asia, representing perhaps 60% of total animal protein intake in Sri Lanka for example.
Inland fishing adds vital income for irrigation farmers in Sri Lanka, many of whom have subdivided their land and water holdings between their children over the years. The industry directly benefits 50,000 rural people, but overall annual yield of inland fish declined from a peak of 39,000 t in 1989 to 12,000 t by 1994 because of bureaucratic changes. The result was lower incomes for fishers and higher prices for fish, penalising the poor. In a new thrust, the government now aims for a yield of 48,000 t by year 2000.
A lake or reservoirs carrying capacity for fish may be determined by such factors as dimensions, age, water renewal rate, supply of nutrients and organic carbon, temperature profile, pH, salinity and biochemical oxygen demand. The factors relationship with catchment land-use, fish productivity, catch per unit effort and local regulations needs further study, especially in the tropics and southern hemisphere.
Systematically organised information is not generally available about the hydrology, limnology and catchment characteristics of many water bodies in either Sri Lanka or Victoria. However, predictive equations have now been developed for individual reservoirs in Asia and their scientific management has increased fish yields. This ACIAR-funded project aims to derive similar predictive indices that will apply to a range of water bodies of various sizes and ages in both Sri Lanka and Australia. Sri Lankan reservoirs range from below 2 ha to over 324 ha in size; one reservoir is roughly 2300 years old.
The researchers, from Kelaniya University in Sri Lanka and Deakin University near Melbourne, will use a GIS to marshall data already available for lakes and reservoirs in the GoulburnMurray district of Victoria and for ten reservoirs in each of two districts of Sri Lanka. They will formulate surplus-yield models based on those data. The team will obtain satellite-sensed information, via Landsat and SPOT, on geographic and water quality characteristics for these and other local water bodies, and check it using on-ground measurements and other models. There will be interviews and questionnaires to discover all the uses of the water bodies and their catchments, and the views of all groups and authorities involved.
Sri Lankan permanent reservoirs carry Tilapia, an introduced vegetation-eating fish that is self-recruiting. In Victorian lakes and reservoirs, which are relatively cool, this project will focus on the recreational fishing of introduced salmonids such as trout, maintained from hatchery stock.
The project will also experiment with cage-culture of carp in Sri Lanka and silver perch in Victoria. Techniques will be developed for growing this years fry into fingerlings (1013 cm long) in cages set in selected publicly-owned permanent waters, without damaging the local ecology. Fingerlings will be released into seasonal reservoirs when they fill the next year, for later recapture as food before the water disappears.
Commercial fish-farming is intensive in Australia, but were public waters to be used for cage culture of silver perch to stock warm-water irrigation water storages, the industry could be low-cost. This could enable Australian irrigation farmers to diversify and improve rural incomes.
The researchers hope for a two-way flow of information with all relevant sectors of community and government in Sri Lanka and Australia throughout the project. Apart from training for Sri Lankan staff, and improved fish production with associated lower prices to consumers, the project should produce a review of management and stocking strategies for public waters, and workable cage-culture guidelines. The work should be applicable to the reservoir fisheries burgeoning across Asia, Africa and South America.
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