Silky sharks (Carcharhinus falciformis, Carcharhinidae) are currently the second</p><p>most harvested shark species in the pelagic longline fisheries and populations are declining. This</p><p>species is currently managed as a single stock per Regional Fisheries Management Organization</p><p>due to a lack of data on stock delineations suggesting other options for population-level</p><p>management. Genetic population structure can resolve dispersal boundaries and provide an</p><p>appropriate foundation for defining distinct stocks, which is crucial for any successful wildlife</p><p>management. This study investigated the global stock structure of silky sharks using high-</p><p>throughput sequencing of genomic data from pooled individuals (pool-seq) based on 628</p><p>specimens collected by scientists on research charters, observers aboard commercial vessels, and</p><p>fish markets across 11 circumglobal regions. Single nucleotide polymorphisms (SNPs) indicate significant population structure between all 11 regional samples. FST values calculated from mitochondrial (mtDNA) markers ranged from 0.012 - 0.160 and from 0.014 - 0.035 for nuclear (nDNA) markers within oceans,</p><p>with much higher values between oceans (mtDNA: 0.383 - 0.844, nDNA: 0.042 - 0.078). Many</p><p>pelagic sharks show population structure on the spatial scale of different ocean basins as seen</p><p>here, but these within-ocean results are unprecedented for a pelagic shark and challenge the</p><p>single stock per RFMO management scheme currently in place. Here we report evidence for</p><p>multiple stocks within the jurisdiction of each of the regional fisheries commissions. These</p><p>results argue that multiple stocks per RMFO need to be established to ensure these smaller stocks</p><p>are not over exploited.
