Population genetics of tunas

Abstract

Population genetic studies on tunas are reviewed. These studies have focused on phylogenetic reconstructions, species identifications and stock delineation, and have used tools ranging from blood group and allozyme analysis to PCR‐aided examination of mitochondrial DNA variation. Both allozyme and mtDNA approaches show tunas in the genus Thunnus to be very closely related to one another, but also indicate that the two presently recognized subspecies of northern bluefin tuna, Thunnus thynnus thynnus and T. t. orientalis, in fact may be worthy of species status. These techniques also permit the unequivocal recognition of specimens, which is not always possible on morphological grounds. However, it is arguable that, until recently, tunas have not received their due attention from geneticists given their commercial significance and the need for information on stock structure to ensure sustainable management. This may be because tunas are known to be highly vagile and therefore levels of population differentiation are expected to be low. None the less, population subdivision has been recorded in several species (skipjack, yellowfin, albacore), although this tends to be on a broad (intra‐ or inter‐oceanic) rather than on a more local scale. New molecular tools, including the PCR‐based analyses of nuclear genes and microsatellite loci, are yielding new, highly polymorphic markers, and will enable more powerful analyses of stock structure than have hitherto been possible.