Spatio-temporal trends of sailfish, Istiophorus platypterus catch rates in relation to spawning ground and environmental factors in the equatorial and southwestern Atlantic Ocean

Spatial and temporal trends of sailfish catch rates in the southwestern and equatorial Atlantic Ocean in relation to environmental variables were investigated using generalized additive models and fishery-dependent data. Two generalized additive models were fit: (i) spatio-temporal', including only latitude, longitude, month, and year; and (ii) oceanographic', including sea surface temperature (SST), chlorophyll-a concentration, wind velocity, bottom depth, and depth of mixed layer and year. The spatio-temporal model explained more (average similar to 40%) of the variability in catch rates than the oceanographic model (average similar to 30%). Modeled catch rate predictions showed that sailfish tend to aggregate off the southeast coast of Brazil during the peak of the spawning season (November to February). Sailfish also seem to aggregate for feeding in two different areas, one located in the mid-west Atlantic to the south of similar to 15 degrees S and another area off the north coast of Brazil. The oceanographic model revealed that wind velocity and chlorophyll-a concentration were the most important variables describing catch rate variability. The results presented herein may help to understand sailfish movements in the Atlantic Ocean and the relationship of these movements with environmental effects.