Modelling the impacts of environmental variation on the distribution of blue marlin, Makaira nigricans, in the Pacific Ocean

Blue marlin are distributed throughout tropical and temperate waters in the Pacific Ocean. The preference of this species for particular habitats may affect its distribution and vulnerability to being caught. The relationships between the spatial pattern of blue marlin abundance and oceanographic conditions, which may be influenced by climate change, were examined using generalized additive models fitted to catch and effort data from longline fisheries. Distributions of blue marlin density, based on combining the probability of presence and abundance given presence, indicate that there is annual variation in the distribution of blue marlin and that the population apparently moved east during the 1997-1998 El Nino. The interannual variability in blue marlin distribution appears to be associated with El Nino events and is related to shifts in sea surface temperature and the deepening of the thermocline. Models of catch and effort that include oceanographic variables could be used, given predictions from climate models, to explore future changes in distribution, which could then be used to provide management advice related to time-area closures.