A Seascape Approach to Investigating Fish Spillover Across a Marine Protected Area Boundary in Hawaiʻi

Abstract

Marine protected areas (MPAs) can benefit fisheries through export of pelagic eggs and larvae, and the net emigration of adults and juveniles (spillover). Spillover was investigated for a marine protected area on the north shore of Oahu, Hawaii utilizing a seascape approach. This study incorporated habitat variables and underwater visual surveys of fishes and benthos measured at two distinct scales (125 m2 and 1000 m2) inside and outside the protected area at varying distance from the boundary. The relationship between fish biomass from small-scale surveys and key habitat variables was found to account for a large portion of the variability for both resource (targeted) fish species (17%) and non-resource fish (28%). The remaining variation in resource fish biomass was significantly correlated with distance from the MPA boundary showing a decreasing gradient from inside to outside (r²=0.34, p<0.01), indicating fish spillover at a local scale (<1km). In contrast, non-resource fish biomass demonstrated no such relationship (p=0.45). The evidence of spillover based on the small-scale surveys was corroborated by results from large-scale surveys, which also showed a significant relationship (r2=0.30, p<0.01) between resource fish biomass and distance from the MPA boundary. In addition, observed spatial distribution of fishing effort was consistent with fishers responding to biomass gradients across MPA boundaries. Fish spillover can help mitigate costs associated with the establishment of marine protected areas in terms of lost fishing area and therefore have a positive effect on the attitudes of fishers towards marine reserves and marine protected areas.