Synergy among oceanographic variability, fishery expansion, and longline catch composition in the central North Pacific Ocean

The fishing grounds of the Hawaii-based longline fleet span over 13 million km(2) in the central North Pacific Ocean. We investigated over 20 years of commercial fishery logbook data and independent observer data to gain an understanding of the variation in magnitude and composition of the fleet's catch on both intra- and interannual scales. We found that the fishery follows a quarterly geographic migration and that the fishery has expanded over time with a 5-fold increase in effort and a spatial expansion primarily to the northeast of Hawaii during the third quarter of the year. The World Ocean Atlas and ocean reanalysis data indicate that waters to the northeast of Hawaii are a particularly effective fishing ground because of the vertical overlap of preferred thermal habitat and fishing gear. Furthermore, we found that the Hawaii-based fleet faced little international competition in this region. The expansion of the fishery has also affected catch composition, resulting in discard rates that exceed target catch rates. Understanding how catch varies as a result of oceanographic variability and fleet movement can lead to a more efficient, resilient, and cost-effective fishery.