Spatio-temporal genetic dynamics of European hake (Merluccius merluccius) populations from Atlantic fishing grounds

Résumé

The overexploitation of fisheries is a major problem nowadays and therefore scientists and managers try to assess the risks of collapse and to propose strategic plans to improve the sustainability of fisheries. Spatio-temporal genetic analyses of marine resources help to describe the connectivity pattern existing across populations and its temporal stability, so the inclusion of this type of data into strategic plans is increasingly demanded. Present molecular data obtained from microsatellite markers and mitochondrial DNA sequences on European hake (Merluccius merluccius) samples collected from its whole distribution range during the last decade, have allowed to establishing important eco-biological properties of this fishery. The macroscale pattern of connectivity recovered upon a mitochondrial clock situates the initial divergence between populations of the two main European basins in the Late Pleistocene (ca. 150,000 yr bp). The Atlantic hake conforms a single panmictic population extending from Northern Ireland to the Canarian Sea and only the North Sea population exhibits a limited gene flow with the rest of Atlantic grounds. A southwards latitudinal migration pattern put forward in this thesis, suggests that a significant biomass displacement occurs systematically from the main spawning grounds of the species in Southwestern Ireland (Great Sole and Porcupine Bank grounds) to northern latitudes of the Southern Stock (Cantabrian Sea). The panmictic scenario proposed for the European hake alternates episodes of metapopulation divergence and therefore its genetic management should ignore unfounded structural criteria. In fact, the interannual monitoring of the genetic diversity of this species, measured through its effective genetic population size, appears to be a good predictor of its genetic status and correlates tightly with biomass trends from interdisciplinary records. The results presented in this thesis are of upmost relevance for the long-term genetic management of this European species regarding its ecological and commercial sustainability.