MOLECULAR RESOLUTION OF MARINE TURTLE STOCK COMPOSITION IN FISHERY BYCATCH - A CASE-STUDY IN THE MEDITERRANEAN

Based on an extensive sampling regime from both nesting populations an d bycatch, frequency analyses of mitochondrial (mt) DNA control region haplotypes in the Mediterranean were used to assess the genetic struc ture and stock composition of the loggerhead sea turtle, Caretta caret ta, in different marine fisheries. The analyses show the following. (i ) In drifting longline fisheries working in Mediterranean pelagic habi tats 53-55% of turtles caught originated from the Mediterranean stock; (ii) In bottom-trawl fisheries all turtle bycatch is derived from thi s regional stock; (iii) This regional stock contribution to fishery by catch suggests that the population size of the Mediterranean loggerhea d nesting population is significantly larger than previously thought. This is consistent with a recent holistic estimate based on the discov ery of a large rookery in Libya. (iv) Present impact of fishery-relate d mortality on the Mediterranean nesting population is probably incomp atible with its long-term conservation. Sea turtle conservation regula tions are urgently needed for the Mediterranean fisheries. (v) The sig nificant divergence of mtDNA haplotype frequencies of the Turkish logg erhead colonies define this nesting population as a particularly impor tant management unit. Large immature and adult stages from this manage ment unit seem to be harvested predominantly by Egyptian fisheries. (v i) Combined with other data, our findings suggest that all the nesting populations in the Mediterranean should be considered as management u nits sharing immature pelagic habitats throughout the Mediterranean (a nd possibly the eastern Atlantic), with distinct and more localized be nthic feeding habitats in the eastern basin used by large immatures an d adults. (vii) Between the strict oceanic pelagic and the benthic sta ges, immature turtles appear to live through an intermediate neritic s tage, in which they switch between pelagic and benthic foods.