Using fisheries data to model the oceanic habitats of juvenile silky shark (Carcharhinus falciformis) in the tropical eastern Atlantic Ocean

Abstract

Investigating the relationship between species and environmental conditions is key for the correct management of highly migratory large pelagic species like silky shark (Carcharhinus falciformis). This species is currently ranked as vulnerable by the International Union for Conservation of Nature and the population trend may be decreasing globally. Tuna fisheries annually catch around 5 million tons worldwide but may have effects on the ecosystem, including impacts on certain sensitive non-target species. We provide the first insights into the environmental preferences of silky shark in the Atlantic Ocean by modelling their presence from tropical tuna purse seine observer data (-7500 fishing sets between 2003 and 2015) with a set of biotic and abiotic oceanographic factors, spatial-temporal terms and fishing operation variables. Oceanographic data (sea surface temperature, sea surface temperature change, salinity, sea surface height, chlorophyll-a, chlorophyll-a change, oxygen, and current information such as speed, direction and eddy kinetic energy) were downloaded and processed from the EU Copernicus Marine Environment Monitoring Service. Results provide information on the hotspots dynamics of silky shark as well as its habitat preferences. Models detected a significant relationship between seasonal upwelling events, mesoscale features and silky shark presence and suggested strong interaction between productive systems and the spatial-temporal distribution of the species. The model also highlighted both persistent (i.e. Gabon) and temporary areas (i.e. Guinea and southern-central tropical Atlantic Ocean) for silky shark in the region. This information could be used to assist tuna regional fisheries management organizations in the conservation and management of this vulnerable non-target species.