Investigating the Spillover Effect for a Marine Protected Area in Hawai'i

Marine protected areas (MPAs) are widely utilized as a management tool to conserve biodiversity and to protect and restore fish populations within their borders. Another potential benefit of MPAs is that they supplement adjacent fisheries through two primary mechanisms: increased production due to export of pelagic eggs and larvae, and the net emigration of adults and juveniles (spillover). While it is generally accepted that larval export provides greater overall fishery benefits, adult spillover can mitigate costs associated with marine reserves providing incentive for fishermen to accept this form of management. This effect was investigated for a marine reserve on the north shore of Oahu in the Hawaiian Islands. Underwater visual surveys were conducted both inside and outside of the MPA at varying distances from the boundary. Habitat information was also collected at each transect. The relationship between fish assemblage metrics and habitat parameters at two distinct scales (in situ and remotely sensed) was explored and found to account for a large portion of the variability. The remaining variation in fish abundance and biomass was correlated with distance from the reserve boundary showing a decreasing gradient from inside to outside. This indicates the emigration or spillover of adult fish. These results improve understanding of the ecological and fishery effects of marine reserves in Hawaii. Lessons learned can help inform MPA design, ecosystem-based management, and marine spatial planning.