Effects of intense fishing pressure on an assemblage of coral reef fishes

Abstract

Fishing is the most important exploitative activity on coral reefs.Despite this, there are few direct tests, utilizing manipulative or natural experiments, of the impact of fishing on coral reef fish assemblages.This paper documents a natural experiment in the central Philippines: a dramatic increase in fishing pressure within a 750 m long marine reserve, previously protected from fishing for 10 yr (1974 to 1984).In 1983, the site had a significantly higher abundance of fishes, particularly those considered to be favoured targets of fishermen (e.g.serranids, lutjanids, lethrinids), than similar sites which were fished.Abundances were estimated by visual census within the reserve and at 3 control sites.In early 1984, protective management broke down and fishing by up to 100 municipal fisherman began, using traps, hand-lines, gill-nets, spears and occasionally more destructive, non-selective fishing methods, such as explosives and drive nets.The reserve and control sites were recensused after 18 mo of fishing in the Sumilon Island reserve.There were decreases in abundance of favoured targets of fishermen and a significant change in community structureincluding significant decreases in both species richness and densityof the coral reef fish assemblage inside the reserve but not at the 3 control sites.Species which contributed most to the change in community structure were not favoured targets and had not constituted a large proportion of yield in previous years Significant decreases in abundance of small, schooling planktivores and benthlc feeding chaetodontids, and significant increases in abundance of small labrids and large scarids, were related largely to the effectiveness of explosives and drive nets against planktivores and herbivores and degradation of the shallow benthic habitat caused by both these methods.Thus, the intense fishing pressure had both direct and indirect effects and a far wider impact on the fish assemblage than the predicted significant decreases in abundance of target species.