Mesoscale cyclonic eddies and pelagic fisheries in Hawaiian waters

The combination of prevailing northeasterly tradewinds and island topography result in the formation of vigorous, westward propagating cyclonic eddies in the lee of the Hawaiian Islands on time scales of 50-70 days. These mesoscale (~10² km) features are nowhere more conspicuous or spin up more frequently than in the Alenuihaha Channel between the islands of Maui and the Big Island of Hawaii. Like other open-ocean eddies, their biological impact can be significant, although Hawaii´s open-ocean, wind driven features dynamically contrast the well-studied cold core current-generated eddies such as those that spin off the Gulf Stream or the Kuroshio. These latter features characteristically trap or isolate an adjacent water mass retaining its developed floristic composition. Cyclonic eddies in subtropical waters such as around Hawaii vertically displace the underlying nutricline into the overlying, nutrient-deplete euphotic zone creating localized biologically enhanced patches. Direct high-resolution horizontal and vertical observations of these vortices made from satellite and shipboard platforms provide new perspectives on biological enhancement within open-ocean cyclonic eddies are presented. How eddies may directly influence pelagic fish distribution are examined from recreational and commercial fish catch data coinciding with the presence of eddies