Effects of an increase in trap mesh size on an overexploited coral reef fishery at Discovery Bay, Jamaica

Abstract

One of the most popular management tools for Caribbean reef fisheries is a minimum mesh size for traps. It is believed that increasing the mesh size of traps in overexploited fisheries will result in higher catch rates in the long term, but lower catch rates in the short term. This study represents the first attempt to document the short-term and long-term effects of partly replacing small mesh with a larger mesh size in an artisanal coral reef fishery. A community level mesh exchange program was initiated in the Discovery Bay trap fishery in March 1991, whereby active fishers were given large mesh (1.5 inch: 3.8 cm) wire to construct traps in exchange for handing in their small mesh (1 inch: 2.5 cm and 1.25 inch: 3.2 cm) traps. Although the total number of active traps and the total number of hauls per month did not significantly change in the fishery, the proportion of small mesh traps decreased substantially as a result of the mesh exchange program, leading to a concurrent reduction of fishing mortality in smaller sized fish. Changes in the fish populations were examined by comparing catch-per-unit-effort (CPUE as number of fish per trap per haul, and kg per trap per haul); mean size of individual fish; catch composition; and length frequency distributions for the 2 most common species, for both 1.25 inch and 1.5 inch traps in 3 separate 6 mo periods (July to December) in 1990 (10 mo before the implementation of the mesh exchange program), 1991 (immediately after the implementation of the mesh exchange program) and 1994 (3 yr after the implementation of the mesh exchange program). The results indicate that reef fish populations at Discovery Bay, and hence yields to the fishery, have increased in the 3 yr since the mesh exchange program was implemented. The number of fish caught per trap haul has increased; the total weight of the catch per trap haul, at least of the smaller mesh sizes, has increased; the catch composition has shlfted towards larger and more valuable species; the mean size of fish taken by the fishery is larger; and the population of 1 narrow-bodied species investigated has shifted towards larger size classes since the increase in mean mesh size in the fishery. However, despite an increase in the gross catch per week by the trap fishery, catch rates still differ markedly between small and large mesh traps, with small mesh traps catching less per haul but more per week than large mesh traps. As a consequence, fishers still using small mesh traps are benefitting the most from recovery of the reef fish populations, which demonstrates the need for further efforts to eliminate the smaller mesh traps from the fishery.

Evidencia de la recuperación inicial de la comunidad coral en Bahía Discovery, Costa norte de Jamaica

“…In addition, where the insults to coral reef are of a long term humaninduced chronic nature, such as overfishing and land development (Mumby, Hasting & Edwards, 2007), engagement with fisherfolk and land developers is vital to minimise the human-induced threats which are so damaging to coral reefs. Unfortunately, previously successful efforts to engage the local fisherman in controlling catches around Discovery Bay (Sary et al, 1997) have not been maintained, and it may be that the development of a sustainable Discovery Bay Marine Protected Area is the only solution.…”

Ocean surgeonfish Acanthurus bahianus. II. Fishing effects on longevity, size and abundance?

“…Koslow et al (1989) found large declines in catches of acanthurids (all species combined, no separate information on Acanthurus bahianus) in heavily fished areas of southern Jamaica between 1969to 1973and 1986. Sary et al (1997 found that, following 4 yr of use of traps with an increased mesh size (which reduced catchability of small fish) at northern Jamaica, catch rates (biomass) of acanthurids (all species combined) increased, but without a consistent pattern of change in the mean size of A. bahianus.…”

“…Jamaica (published data on body size; Reeson 1983, Sary et al 1997) has a dense human population (2.6 million, 4400 km 2 land, 1240 km 2 reef), and one of the most intensive trap-fisheries in the Caribbean (Munro 1983, Koslow et al 1989, 1994, Sary et al 1997. The human population density in the Bahamas is fairly low (295 000 people on 10 000 km 2 land, 3150 km 2 reef), especially in the general vicinity of Lee Stocking Island (data collection November 1998November , 1999, which is well away from population centers.…”

“…Reef-fisheries at Jamaica are intense, and based on traps (Munro 1983, Koslow et al 1989, 1994, Sary et al 1997. Koslow et al (1989) found large declines in catches of acanthurids (all species combined, no separate information on Acanthurus bahianus) in heavily fished areas of southern Jamaica between 1969to 1973and 1986.…”

“…Besides being one of the most widespread tropical west Atlantic shore fishes, A. bahianus is one of the commonest small (it reaches ~600 g), herbivorous reef-fishes throughout its range. In parts of the Caribbean where there are intensive trap-fisheries for reef-fishes, A. bahianus is a major component of trap-catches (Munro 1983, 2000, Reeson 1983, Koslow et al 1989, 1994, Recksiek et al 1991, Beets 1997, Sary et al 1997, Garrison et al 1998, Robichaud et al 2000, is important in subsistence fisheries (Randall 2002), and is of minor commercial significance (Froese & Pauly 2004). Trapping is the primary method by which this species is fished.…”