GENETIC CONSEQUENCES OF SELECTIVE FISHING

Selective fishing, removing mainly old large fish, leaves young fast g rowing and early maturing individuals nearly intact. This leads to an increased rate of generations' succession,''rejuvenation'' of spawning stocks, to decrease in their numerical size and biomass. Such dynamic s is typical for species with diverse ecology. A hypothesis, according to which reorganizations of universal adaptive system, that determine s individual differences in growth and maturation rates, are responsib le for uniform changes in biology of populations under selective fishi ng pressure, is proposed. These differences turned out to be correlate d with intrapopulation sex differentiation and levels of allozyme geni c diversity in sockeye salmon Oncorhynchus nerka (Walbaum), pink salmo n O. gorbuscha (Walbaum), and some other salmonid species. The ratio b etween intra- and inter-group components of genetic diversity is maint ained at a stable, optimal level by fine subpopulation structure, orde red in time and space, in case of natural reproduction of a population system. Disproportional removal of large, usually more homozygous ind ividuals, leads to an increase of heterozygosity, acceleration of grow th and maturation rates with negative consequences. Interpopulation ge netic differences are disappearing. Still, this process is adaptive;an d timely termination of unfavorable external impact leaves a chance fo r the restoration of genetic structure and normalization of reproducti on of populations' gene pools. Selection against small, more heterozyg ous individuals (which may occur at hatcheries), leads to inbreeding. Intrapopulation genetic diversity declines, while interpopulation dive rsity increases. This process is inadaptive, and probably leads to irr eversible degradation of artificially maintainerd populations. Genetic foundations of rational fishery are considered in concluding part of the paper, and practical recommendations are given.