Documenting historical changes in shark fisheries near Islas Marias, Mexico, using fishers' local ecological knowledge

Many shark species and populations are threatened globally due to human actions. Protecting these top predators is crucial to maintaining healthy marine ecosystems; however, for many habitats, long-term, historical datasets necessary to track population changes are lacking. In Islas Marias, Mexico, where shark fishing has occurred for decades, data on landings by species remain unavailable and the presence of a prison in the archipelago from 1905 to 2019 has hindered monitoring efforts. We used a synthesis of fishers' local ecological knowledge (LEK) to address this knowledge gap about changes in shark populations near Islas Marias. Using LEK documented from interviews with 82 fishers, we cataloged shark species diversity, catch, and perceived relative abundance in the region. Fishers reported the presence of 15 species and one genus of sharks near Islas Marias. Overall, catch sizes and perceived relative abundance trends derived from interviews suggest that populations of sharks near Islas Marias have been in decline since at least the 1960 s. Interview participants attributed shark declines to envi-ronmental, social, and market factors. These results highlight the importance of fishers' expert knowledge in reconstructing species population trends.