The effect of marine protected areas on an exploited population of sex-changing temperate reef fish: an individual-based model

Abstract

The effect of two marine protected areas (MPAs) on roman Chrysoblephus laticeps (Sparidae), an exploited reef-fish species inhabiting the South African temperate south coast, was simulated with a spatially explicit, individual-based model based on geographically correct habitat distribution. The model domains were small compared with the dispersal range of pre-recruits, and recruitment was held constant. Adult fish movement rules were based on the results of high-resolution markand-recapture and telemetry studies. Fish densities, age-structure and life-history parameters were derived from comprehensive underwater surveys and biological analyses. The model included the effect of fishing on size-at-sex change. The results indicate a recovery of fish abundance-per-recruit, size frequency and sex ratio to, or close to, pre-exploitation levels within the protected areas 10 years after the implementation of both MPAs. Results suggest that, for resident species such as roman, even small MPAs (6 km²) can offer protection. The small exchange of post-recruit fish into the adjacent areas results in negligible improvement (1%) of catches. The MPAs support more and larger spawning fish, which may improve recruitment into adjacent fished areas.

Keywords: Chrysoblephus laticeps; fisheries management; individual-based model; marine protected areas; South Africa, spillover

African Journal of Marine Science 2008, 30(2): 337–350