Modelling the impacts of environmental variation on habitat suitability for Pacific saury in the Northwestern Pacific Ocean

We developed habitat suitability index (HSI) models for two size classes of Pacific saury Cololabis saira in the Northwestern Pacific Ocean. Environmental data, including sea surface temperature, sea surface height, salinity, and net primary production, and catch and effort data from Taiwanese distant-water stick-held dip net fisheries during the main fishing season (August-October) during 2002-2015 were used. Habitat preferences and suitable habitat area differed between size classes. The suitable habitat was located between 40-47.5 degrees N and 145-165 degrees E for large-sized Pacific saury but encompassed a greater area (35-47 degrees N and 140-165 degrees E) for medium-sized Pacific saury. Both size classes were affected by substantial interannual variation in the environmental variables, which in turn can be important in determining the potential fishing grounds. We found a significant negative relationship between the suitable habitat area and the Nino3.4 indices with a time-lag of 6 months for the large-sized (r = -0.68) and medium-sized (r = -0.42) Pacific saury, respectively, as well as the total landings of Pacific saury by all fishing fleets (r = -0.46). As remotely-sensed environmental data become increasingly available, HSI models may prove useful for evaluation of possible changes in habitat suitability resulting from climate change or other environmental phenomena and in formulating scientific advice for management.