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Pelagic sharks in parks: Marine protected areas in the Eastern Tropical Pacific provide limited protection to silky sharks tracked from the Galapagos Marine Reserve

Abstract:

Marine protected areas (MPAs) are being increasingly delineated to protect at risk species, however, their effectiveness in protecting wide-ranging species is uncertain. Silky sharks (Carcharhinus falciformis) have experienced large declines in the Eastern Tropical Pacific, and their conservation may benefit from the recently expanded network of MPAs in the region. To examine time spent by silky sharks in MPAs and overlap of shark movements with fisheries, we tracked 38 silky sharks from the Galapagos Marine Reserve (GMR) with SPOT tags for up to 639 d. Time spent within MPAs varied little between the wet (Dec-May) and dry seasons (Jun-Nov), with sharks showing periods of residency in the GMR during both seasons; males and females spent ~45 % and 33 % of their time within the GMR, respectively. However, the silky sharks spent comparatively little time in other MPAs within the region; total time within all MPAs was 44–55 %. Combining silky shark space use with apparent fishing effort data from Global Fishing Watch revealed that sharks experienced the most fishing effort during the dry season within Ecuadorian waters north of the Hermandad Marine Reserve. Sharks did not encounter any concentrated areas of fishing effort during the wet season; however, Global Fishing Watch data severely underestimate fishing effort in the region. Overall, for a wide-ranging species, silky sharks spent a high proportion of time within the protected waters of the GMR, but their movements extended far beyond the GMR and other marine reserves, putting them at risk from commercial fisheries operating in the region.