LOW GENETIC-VARIABILITY IN A WIDELY DISTRIBUTED AND ABUNDANT CLUPEID SPECIES, SARDINELLA-AURITA - NEW EMPIRICAL RESULTS AND INTERPRETATIONS

Considering the wide geographic distribution and the catches of Sardin ella aurita, the observed allozyme diversity (H=0.011) is strikingly s mall. Potential explanations for this low gene diversity, which includ e restrictions on effective population size owing to variance in repro ductive success, demographic instability, historical bottlenecks in po pulation size, selection, and technical artifacts are examined and qua ntified. This quantification, though rough, shows that no single Facto r can account for the lack of diversity. However, demographic instabil ity of S, aurita, especially if this instability has persisted over ev olutionary time scales, together with much greater than Poisson varian ce in individual reproductive success, could account reasonably for th e results. Pleistocene reduction of population size seems also a neces sary co-factor. Technical artifacts, mostly scoring difficulties linke d to liver autolysis, are considered also and analysed in different cl upeid species. (C) 1998 The Fisheries Society of the British Isles.