Should I stay or should I go?: fish larvae retention in the Hawaiian archipelago

In Hawai‘i, Marine Protected Areas (MPAs) have been established to protect bottom fish stocks. MPAs are a powerful management tool, providing a range of ecological benefits within and outside their boundaries. It is known that larval transport is an important mechanism for MPA spillover benefits. Studies accounting for the physical processes that transport fish larvae across MPA boundaries, however, are scarce and often inadequately considered in the designation process. Our research corrects this lacuna by describing how circulation influences the dispersal of fish larvae in the Hawaiian archipelago. Outputs from 3D models that simulate ocean circulation (ROMS and HYCOM) were coupled offline with a biological model depicting adult spawning strategy, larval development, swimming behavior, mortality and settlement (BOLTS). Spawning and receiving areas of larvae were considered to be the 10 km wide region around the islands and larvae were tracked for 30 days. Organisms older than 15 days where considered retained after spending a day within the limits of a receiving site. Results indicate that local retention is generally higher than larval export. Also, larval exchange between the main Hawaiian islands and the Papahanaumokuakea Marine National Monument or Johnston Atoll is null. Considering only the MPAs as release and receiving sites, local retention is bigger than export, suggesting that MPAs are not supplying each other. When all receiving sites are considered, larval export from MPAs to fishing sites is high, although some areas are more efficient than others in producing larvae that will be overall retained in the archipelago. Seasonal variability in overall retention was not observed for 2005. These results corroborate that larval dispersal changes with the location of the spawning/receiving sites, and must be taken into account in future MPA designations.