Challenging the knowledge bio-based fisheries of tropical tuna stocks: assessing genomic population structure in yellowfin (Thunnus albacares)

Tropical tunas (TT) account for the greatest part of world tuna catches but their stock biomass declined ca. 60% from 1954 to 2006, increasing the risk of ecological/economic extinctions. The monitoring and management of TT stocks is currently jeopardized because four international and intergovernmental Regional Fisheries Management Organizations (RFMOs) are engaged, each operating independently in its jurisdictional area. The effort of RFMOs to manage and conserve TT lies on stock assessments systematically distorted by insufficient fishery and population biological data. Despite the relevance of TT, their genetic population structure is not well resolved yet, with several studies leading to discordant evidence. In particular Yellowfin tuna, Thunnus albacares (YFT) population structure is still poorly understood and they have been considered to be highly mobile and consist of a single panmictic spawning population for the purposes of stock assessment and management in each ocean. However as suggested by some studies in Indian Ocean there may be distinct population structure at a much smaller scale than has generally been considered for highly migratory species. The YFT genetic population structure will be investigated at global scale (between- and within-ocean), using next-generation sequencing (2b-RAD method for genotyping by sequencing) through examination of Single Nucleotide Polymorphisms (SNPs). This approach can represent a major advancement over classical techniques used until now (i.e. based on allozymes, DNA microsatellites and mitochondrial DNA) in order to reveal the YFT stock structure between and within each ocean. The novel genomic data that will be generated can potentially reveal YFT population structure at a level not possible through classical latter approaches with significant implication for YFT stock assessment and management. In fact a carelessness of the proper genetic structure might lead to the over-exploitation and depletion of some populations with dramatic consequences for the long-term conservation and sustainable use of YFT stocks.