Patterns of temporal genetic variability in the overexploited Mediterranean stock of Atlantic bluefin tuna (Thunnus thynnus)

The estimation of genetic variability and the identification of temporal variation in genetic structure of a population is crucial for the conservation of endangered species undergoing strong overexploitation, such as the Atlantic bluefin tuna Thunnus thynnus. Fishery is having strong impact on bluefin tuna population abundance and serious consequences on genetic potential of Mediterranean populations may occur. Owing to the interest in the conservation and ownership of bluefin tuna stocks, it becomes critical to resolve structure and dynamics of populations over time. A molecular approach becomes fundamental to unlock ancient genetic features of populations and for genetic comparisons to modern populations. This can be decisive for assessing genetic and demographic changes in fishery resources overexploited since decades. The demonstration of loss of genetic variability in wild populations is empirically limited by lack of samples before heavy overexploitation started. Although rare, archived samples represent a unique opportunity to access ancient populations. Comparative analyses of genetic diversity at 8 microsatellite loci in ancient (skeletal records collected from 1911 to 1926 by Massimo Sella) and modern samples (from fishery vessels) of Mediterranean bluefin tunas revealed a temporal stability of genetic diversity over about 90 years and more than 50 years of industrial exploitation of the stock. On the other hand, significant changes in the genetic structure of Central Mediterranean bluefin tuna samples were detected. The results of such work can argue for an evidence that, in the Mediterranean, stock overexploitation has not yet corrupted the genetic potential of such relevant fishery resource and that bluefin tunas are not fully panmictic. Overall, the results did outcome from analysis of temporal genetic variation in fishery resources that include comparisons between ancient unexploited and modern (over)exploited populations can really contribute to assess the conservation of fish stock