The effect of a closed area and beach seine exclusion on coral reef fishcatches

摘要

Fish landing data from the Mombasa Marine National Park (MNP) and a marine reserve exploited by various gears were studied over a 5-yr period to determine the influence of the closed area and different gears in fisheries. The number fishing and boats per landing site was constant, but total and catch per unit effort progressively declined in all sites on an annual basis irrespective of the existence of a marine reserve, exclusion of the beach seines or use of gear. Differences between landing sites were most pronounced when analysed on a catch per area as opposed to the more standard catch per fisherman, suggesting compensation in human effort when catches decline. A marine reserve next to a closed area that excluded beach seines had the highest catch per area (5.5 kg ha(-1) month(-1)) despite having the highest density of fishermen (0.07 +/- 0.02 fishermen ha(-1) month(-1)). The annual rate of decline in the catch was lower than the other sites at around 250 g day(-1) compared with 310-400 g day(-1) in the other sites. One landing site, which excluded beach seine landings for mure than 20 yrs, had a high catch per area (similar to5.3 kg ha(-1) month(-1)), but after experiencing a doubling in the effort of other gears (line, speargun and trap), the catch per fisherman and area were reduced. Environmental or habitat degradation and excessive effort remain the most likely explanation for the overall declines in catch from 1995 to 1999. Closed areas and beach seine exclusion have the potential to increase catch rates, but the first often reduces the total fishing area and possibly leads to a loss of total catch, at least on a time scale of less than 10 yrs. The exclusion of beach seines can lead to an increase in other gear types that can also cause reductions in catch.