Abstract

Pontastacus cubanicus is commercially important in the waterbodies of the lower Don area in Russia. In the 1970s the amount of the crayfish caught averaged 75 tons/year, while in recent years the catch has not been exceeding 10 tons. The pollution of the waterbodies by toxicants in 1991-1992 had a negative effect on the populations of crayfish and their feed organisms (zooplankton, benthos). Stabilization of the ecological situation by 1997 has contributed to the extension of the habitats and to an increased abundance of Pontastacus cubanicus. The highest density of the crayfish was observed in the upper reaches of the River Sal with its tributaries (700-1000 specimens/ha); 400 sp./ha were found in the Ust-Manych Reservoir, while in the Don and in the reservoirs of Proletarskoye and Veselovskoye, despite their pure water, the density was low (65-150 sp./ha). The bulk of the trappable population belonged to specimens of commercial size (53-59%). In the waterbodies of intensive catch the middle-sized (30-40%) and small specimens (16-33%) prevailed, while in the waterbodies of low level of catching large specimens were abundant (57-95%). The average length of the crayfish ranged from 10.2 to 15.4 cm and the weight from 35.2 to 113 g. Their physiological state was good: the concentration of protein in the haemolymph amounted to 5.7-6.76 mg%, that of calcium made up 10.4-10.8 mM/l; the percentage of juvenile blood-cells is 20-28; the criterion of viability was 2-2.65 and the haemocytes were not observed to change. At present the biomass of crayfish in the waterbodies of the lower Don amounts to 140 tons. It decreased 4 times compared to the 1980s; in polluted waterbodies the biomass dropped 17 times with the catches coming to a mere 23-25 tons.

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