Partial Protection - Does It Work? A Kenyan Example
MCCLANAHAN CO-AUTHOR OF LONGEST FISHERY CLOSURE STUDY
Tim McClanahan, Pew Fellow and Senior Conservation Zoologist at the Wildlife Conservation Society, has co-authored a study examining four closures in Kenya’s coral reef fisheries that were instituted at different times and produced a nearly continuous recovery for over 37 years. McClanahan and his colleagues found that certain species of fish increased their numbers up to 10 years after the closures and then remained unchanged; whereas fishable stock reached its peak only after 25 years. Their findings suggest that coral reef fishery recovery it is a slow process and that the only way to maintain fisheries stocks might be to permanently close the areas.
TOWARD PRISTINE BIOMASS: REEF FISH RECOVERY IN CORAL REEF MARINE PROTECTED AREAS IN KENYA
Tim R. McClanahan, Nicholas A. J. Graham, Jacqulyn M. Calnan, and M. Aaron MacNeil. 2007. Toward pristine biomass: Reef fish recovery in coral reef marine protected areas in Kenya. Ecological Applications 17 (4) 1055-1067.
MarineNZ Editor's Note: This study is set in a tropical setting looking at coral reef species and ecology, however there are some direct comparisons that can be made here with some of our NZ studies on partial protection that look at the impact of removing top end predators, (by fishing) from sensitive and complex reef systems. In this case some species took 10 years to recover under full protection and significant changes are still be observed under full protection after 30+ years of full protection.
Identifying the rates of recovery of fish in no-take areas is fundamental to designing protected area networks, managing fisheries, estimating yields, identifying ecological interactions, and informing stakeholders about the outcomes of this management. Here we study the recovery of coral reef fishes through 37 years of protection using a space-for-time chronosequence of four marine national parks in Kenya. Using AIC model selection techniques, we assessed recovery trends using five ecologically meaningful production models: asymptotic, Ricker, logistic, linear, and exponential. There were clear recovery trends with time for species richness, total and size class density, and wet masses at the level of the taxonomic family. Species richness recovered rapidly to an asymptote at 10 years. The two main herbivorous families displayed differing responses to protection, scarids recovering rapidly, but then exhibiting some decline while acanthurids recovered more slowly and steadily throughout the study. Recovery of the two invertebrate-eating groups suggested competitive interactions over resources, with the labrids recovering more rapidly before a decline and the balistids demonstrating a slower logistic recovery. Remaining families displayed differing trends with time, with a general pattern of decline in smaller size classes or small-bodied species after an initial recovery, which suggests that some species- and size-related competitive and predatory control occurs in older closures. There appears to be an ecological succession of dominance with an initial rapid rise in labrids and scarids, followed by a slower rise in balistids and acanthurids, an associated decline in sea urchins, and an ultimate dominance in calcifying algae. Our results indicate that the unfished “equilibrium” biomass of the fish assemblage >10 cm is 1100–1200 kg/ha, but these small parks (<10 km2) are likely to underestimate pre-human influence values due to edge effects and the rarity of taxa with large area requirement, such as apex predators, including sharks.
Key words: coral reef ecology, ecological interactions, ecological succession, fisheries closures, fisheries production, fisheries yields, indirect effects, marine reserves, marine protected areas, maximum sustained yield, MSY, spillover