A Fragile Stronghold: Genomics Reveal Angelshark Population Vulnerability in Corsica, a Key Mediterranean Refuge.

Once common in Eastern Atlantic and Mediterranean coastal waters, the angelshark (Squatina squatina) has disappeared from 90% of its historical geographic range over the last century. Populations have drastically declined, likely due to the combined effects of overfishing, coastal habitat destruction, and the species' slow life history traits. The island of Corsica remains one of the last Mediterranean refuges for this IUCN Critically Endangered species, underscoring the need for conservation action. Given the difficulty of observing this benthic shark, we employed genomic methods to investigate the fine-scale spatial genetic structure, genetic diversity, and effective population size. Skin samples were opportunistically collected from accidental bycatch of angelsharks by local fishers in eastern Corsica and genotyped for 9699 Single Nucleotide Polymorphisms. We show that these individuals belong to a single population and exhibit high site fidelity, particularly among females, supporting male-biased dispersal. Genetic relatedness analyses identified 35 close family relationships, with 42% of sampled individuals showing a close relative. Additionally, we revealed multiple paternity within a single litter, suggesting a polyandrous mating system not previously documented in Squatinidae. The estimated effective population size of 290 individuals (95% CI: 209-453) is concerning given the persistent bycatch of hundreds of angelsharks by local artisanal fisheries during the annual spring reproductive aggregation of Spicara smaris. Protecting these ephemeral breeding colonies would not only benefit angelsharks but also help sustain numerous other threatened elasmobranchs and commercially important fish species (i.e., Zeus faber). Our findings highlight the value of integrating genomic tools into the conservation of elusive marine species. Conservation efforts should focus on reducing bycatch through gear modifications, seasonal fishing restrictions, and preserving estuaries. Studying and protecting this Corsican refuge is of paramount importance, as it could serve as a source population for restoring angelshark populations in formerly abundant areas.