Operational oceanography applied to skipjack tuna (Katsuwonus pelamis) habitat monitoring and fishing in south-western Atlantic

Skipjack tuna (Katsuwonus pelamis) ranks third among marine resources that sustain global fisheries. This study delimits the spatiotemporal habitat of the species in the south-western Atlantic Ocean, based on operational oceanography. We used generalized additive models (GAMs) and catch data from six pole-and-line fishing vessels operating during 2014 and 2015 fishing seasons to assess the effect of environmental variables on catch. We also analysed Modis sensor images of sea surface temperature (SST) and surface chlorophyll-alpha concentration (SCC) to describe fishing ground characteristics in time and space. Catch was positively related to thermocline depth (24-45 m), SST (22-24.5 degrees C), SCC (0.08-0.14 mg/m(3)) and salinity (34.9-35.8). Through SST images, we identified that thermal fronts were the main surface feature associated with a higher probability to find skipjack. Also, we state that skipjack fishery is tightly related to shelf break because bottom topography drives the position of fronts in this area. Ocean colour fronts and plankton enrichment were important proxies, accessible through SCC, used to delineate skipjack fishing grounds. Catch per unit effort (CPUE) was higher towards summer (median 14 t/fishing day) due to the oceanographic characteristics of the southern region. High productivity in this sector of the Brazilian coast defines the main skipjack feeding areas and, as a consequence, the greatest abundance and availability for fishing.