Trophic state, fish community and intensive production of salmonids in Alicura Reservoir (Patagonia, Argentina).

TEMPORETTI, P.; ALONSO, M.; BAFFICO, G.; DIAZ, M.; LOPEZ, W.; PEDROZO, F.; VIGLIANO, P.

LAKES & RESERVOIRS RESEARCH AND MANAGEMENT

Blackwell Publishing

Año: 2001 vol. 6 p. 259 - 267

1320-5331

The Governments of the Provinces located in Patagonia, Argentina, promote the intensive breeding of salmonids in the Andean Patagonian Region. Although annual production is low (450 ton year-1), some effects are notorious. Waste produced by salmonids breeding (feed losses, feces and excretion) causes modifications of water quality, sediments and biota due to an increase of nutrients and organic matter concentrations, with the consequent risk of rising eutrophication levels. Possible changes in water composition, sediments, algae and wild fish populations were studied. Sites affected by fish farming showed increased nutrient concentration, phytoplankton and periphyton biomass. Chlorophyll a was a similar at both (affected and unaffected by fishfarms sites) site. Sediments dramatically reflect fish-farm waste inputs: TP and organic matter increased 12 and 4 times, respectively. The species present in the gillnet catches were the autochthonous Percichthys trucha, Odontesthes hatcheri, Diplomistes viedmensis and the introduced salmonids Oncorhynchus mykiss, Salmo trutta, Salmo salar sebago and Salvelinus fontinalis. About 50% of the total catch were salmonids. A major portion of the CPUW was composed by rainbow trout, followed by perca. CPUW obtained for this reservoir agrees with values ranges as proposed by Quirós (1990), for Patagonian reservoirs. Comparing with studies made by Freyre et al. (1991), a variation in catch composition exists. Which consist mainly of an increase in numbers and well being of O. mykiss and a decrease of P. trucha. Presence of fish escaped from hatcheries, recognizable by their erosioned fins was observed particularly in a sampling station near the fish cage systems. Variations in catches could be caused by cyclical changes in fish populations (Wooton, 1991), by direct and indirect effects of intensive fish farming, or by combination of both events and can only be understood through long term studies of catch variations.