Rapid Build‐up of Fish Biomass in a Caribbean Marine Reserve

Abstract

Marine reserves, where fishing is excluded, have been argued to be an effective means of managing complex reef fisheries and of protecting populations of species vulnerable to overfishing. The argument rests on predictions of increases in abundance and size of fishes after the elimination of fishing mortality, which in turn leads to greater egg production per unit of reef and greater export via pelagic dispersal to fishing grounds. This study reports responses of fish populations to area closure in a small Caribbean marine reserve surrounding the island of Saba in the Netherlands Antilles. Part of the reserve has been closed to fishing since 1987, and the remainder is subject only to light fishing. Fish populations were visually censused and sizes of individuals present estimated from counts in fished and unfished areas of the marine park in 1991 and 1993. For four of five commercially fished families, biomass was greater in the unfished area than in the fished. Predictions of greater abundance and size in the unfished area were upheld for many of the species observed. Between 1991 and 1993 overall biomass of commercially important families increased 60%, based largely on increases in abundance between years. The predatory snappers (Lutjanidae) increased 220%. Fishing pressure in Saba was reduced between censuses due to changing employment opportunities. It was notable that populations increased in both fished and unfish ed areas of the park, and the latter is probably an effect of this reduced fishing intensity. Reserves have been suggested as refuges for species vulnerable to overexploitation, especially groupers. Despite protection from fishing, the Saba Marine Park has low population densities of such species, perhaps due to a lack of supply of larvae from unprotected source areas. My study shows that target fish populations may respond swiftly to reductions in fishing pressure and that reserves could play an important role in fisheries management. But protection of vulnerable species is only likely to be successful if networks of reserves are established throughout species ranges to link larval supply and settlement areas.