CAMBIAMENTI TEMPORALI NELLA DIVERSITÀ GENETICA DEL TONNO ROSSO (Thunnus thynnus) DEL MEDITERRANEO

Fishery-based studies of the Atlantic Bluefin tuna (ABFT, Thunnus thynnus) did not reach unambiguous conclusions, leaving open the debate on whether the Eastern stock (i.e. Eastern Atlantic and Mediterranean) is undergoing a serious demographic crisis, which should likely reflect overfishing. In this study we collected contemporary (N=256) and historical (N=206) biological samples of ABFT of the Western Mediterranean sea, the latter dating back to the early 20th century, i.e. before the shift to industrial fishery. Measure of genetic differentiation and a general heterozygote deficit suggested that differences exist among subpopulations, both now and a century ago, and hence that the Western Mediterranean tuna do not represent a single, panmictic population unit. Statistics designed to infer changes in population size, both from current genetic variation and from comparisons between historical and contemporary populations, did not provide consistent evidence for recent population bottlenecks. In principle, these results might be compatible with a demographic crisis which has not been severe enough to significantly deplete the ABFT allele pool yet. However, various kinds of considerations concur in suggesting a simpler interpretation of these results, namely that the available genetic data do not support a major stock decline in the Western Mediterranean ABFT.