Spillover of exploitable fishes from a marine park and its effect on the adjacent fishery

The role of a marine protected area in enhancing local fisheries, through t he emigration or spillover of exploitable fishes, was studied in a coral re ef park (Mombasa Marine Park, Kenya) and fishery over a seven-year period d uring a time when the park's border changed and pull seines were eliminated . We measured catches before and after the park's establishment and during the management changes and compared these catches with the unmanaged side o f the park. Additionally, we placed baited traps on both sides of the park over a full tidal cycle which allowed us to measure the spillover from the park compared to the deeper, rougher, and less fished reef edge. The total wet mass of catches per trap, the mean size of the trapped fish, and the nu mber of fish species caught per trap declined as a function of the distance away from the park edge on both the southern and northern sides. However, this relationship was truncated on the unmanaged side which also had smalle r catches, smaller fish, and fewer species than the managed side. Trap fish ers on the managed side adapted to the spillover by increasing the traps pe r fisher, which had the effect of reducing the catch per trap. Tides and re ef morphology also appeared to interact and influenced catches, but we foun d no relationships between catches and benthic substratum cover, which was usually dominated by seagrass and sand. Spillover from the deeper reef edge was evident for the managed but not the unmanaged side of the park, but ma y be due to differences in reef morphology interacting with tidal patterns rather than management. On the managed side, the park significantly increas ed the catch per fisher and catch per area by >50%, but even after the park 's size was reduced, the total catch was reduced by similar to 30%. The red uced park was still similar to 50% of the total area. Consequently, the cat ch per area increase was insufficient to compensate for the lost area over this early period of the park's establishment. Spillover was greatest for t he dominant fisheries species. These were moderately vagile species in the rabbitfish (Siganidae; herbivores), emperors (Lethrinidae; carnivores), and surgeonfish (Acanthuridae; herbivores) families, which had instantaneous e migration rates from the park to the reserve fishing ground of similar to0. 5. Our field survey, combined with previous modeling studies, based on adul t emigration rates from marine reserves, suggests that tropical fisheries d ominated by rabbitfish, emperors, and surgeonfish should be enhanced by clo sed areas of similar to 10-15% of the total area. The optimal protected are a may increase if larval export is important, but the predicted response sh ould not be measurable for >10 years, beyond the length of our study, as br eeding stock develop inside protected areas.