TY - JOUR

T1 - Malthusian overfishing and efforts to overcome it on Kenyan coral reefs

AU - McClanahan, Tim R.

AU - Hicks, Christina C.

AU - Darling, Emily S.

PY - 2008/9

Y1 - 2008/9

N2 - This study examined trends along a gradient of fishing intensity in an artisanal coral reef fishery over a 10-year period along 75 km of Kenya's most populated coastline. As predicted by Malthusian scenarios, catch per unit effort (CPUE), mean trophic level, the functional diversity of fished taxa, and the diversity of gear declined, while total annual catch and catch variability increased along the fishing pressure gradient. The fishery was able to sustain high (similar to 16 Mg.km(-2).yr(-1)) but variable yields at high fishing pressure due to the dominance of a few productive herbivorous fish species in the catch. The effect of two separate management strategies to overcome this Malthusian pattern was investigated: fisheries area closure and elimination of the dominant and most "competitive'' gear. We found that sites within 5 km of the enforced closure showed significantly lower total catch and CPUE, but increased yield stability and trophic level of catch than predicted by regression models normalized for fishing effort. Sites that had excluded illegal beach seine use through active gear management exhibited increased total catch and CPUE. There was a strong interaction between closure and gear management, which indicates that, for closures to be effective at increasing catch, there must be simultaneous efforts at gear management around the periphery of the closures. We propose that Malthusian effects are responsible for the variation in gear and catch and that active management through reduced effort and reductions in the most competitive gear have the greatest potential to increase the functional and trophic diversity and per-person productivity.

AB - This study examined trends along a gradient of fishing intensity in an artisanal coral reef fishery over a 10-year period along 75 km of Kenya's most populated coastline. As predicted by Malthusian scenarios, catch per unit effort (CPUE), mean trophic level, the functional diversity of fished taxa, and the diversity of gear declined, while total annual catch and catch variability increased along the fishing pressure gradient. The fishery was able to sustain high (similar to 16 Mg.km(-2).yr(-1)) but variable yields at high fishing pressure due to the dominance of a few productive herbivorous fish species in the catch. The effect of two separate management strategies to overcome this Malthusian pattern was investigated: fisheries area closure and elimination of the dominant and most "competitive'' gear. We found that sites within 5 km of the enforced closure showed significantly lower total catch and CPUE, but increased yield stability and trophic level of catch than predicted by regression models normalized for fishing effort. Sites that had excluded illegal beach seine use through active gear management exhibited increased total catch and CPUE. There was a strong interaction between closure and gear management, which indicates that, for closures to be effective at increasing catch, there must be simultaneous efforts at gear management around the periphery of the closures. We propose that Malthusian effects are responsible for the variation in gear and catch and that active management through reduced effort and reductions in the most competitive gear have the greatest potential to increase the functional and trophic diversity and per-person productivity.

KW - artisanal fisheries

KW - demographic change

KW - gear use and management

KW - fisheries closures

KW - fisheries yields

KW - Kenya

KW - marine protected areas

KW - resource competition

KW - social-ecological systems

KW - FISHERIES MANAGEMENT

KW - FISH COMMUNITIES

KW - MARINE PARK

KW - IMPACTS

KW - BIOMASS

KW - POPULATIONS

KW - PERSPECTIVE

KW - RESILIENCE

KW - SPILLOVER

KW - SYSTEMS

U2 - 10.1890/07-0876.1

DO - 10.1890/07-0876.1

M3 - Journal article

VL - 18

SP - 1516

EP - 1529

JO - Ecological Applications

JF - Ecological Applications

SN - 1051-0761

IS - 6

ER -