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Queen conch, Strombus gigas, in fished and unfished locations of the Bahamas: effects of a marine fishery reserve on adults, juveniles, and larval production

Vera Beach,J. Howard

Published 1997 in Oceanographic Literature Review

ABSTRACT

Marine fishery reserves <MFR'sJ have been set aside in coastal areas throughout the world with the hope ofreversing population decreases commonly observed in many marine resources. In this study. a comparison ofpopulation structure ofthe commer­ cially important gastropod Sfrombus gigas, queen conch. was made between a fished area and an MFR in the Exuma Cays, central Bahamas. There were 31 times more adult conch on the shallow «5 m) Great Bahama Bank in the MFR, and in a survey at 7 depth inter­ vals (to 30 ml on the island shelf in the Exuma Sound, mean adult density was always higher in the MFR, by as much as 15 times. Shell length and lip-thick­ ness measurements indicated that adults in the MFR migrate with age from bank nursery sites into deeper sound water, whereas those on the bank in the fished area were harvested be­ fore reaching water sufficiently deep to protect them from free-diving fisher­ men. Although sparsely distributed ju­ veniles in shallow-water «15 ml habi­ tats of the sound were the primary source ofadults in the fished area, large juvenile aggregations on the bank also contributed to the deep-water adult stock in the MFR. Total larval densities in the MFR were frequently an order ofmagnitude higher than those found in the fished area, and densities oflate-stage larvae were 4 to 17 times higher. Because the surface current along the Exuma Cays shelfflows to the northwest. late-stage larvae found inside the reserve must have been spawned outside the reserve; thus the high densities ofjuvenile and adult conch are the result of natural accumulation of larvae in the area, as well as the result of protection from fishing. Although the fate oflarvae dis­ persed from the reserve is uncertain, it is likely that high numbers ofreproduc­ tive stock and larvae in the reserve have a significant positive effect on populations in the northern Exuma Sound. Designs of reserves that con­ sider ontogenetic requirements of the target species and strategic locations for larval production, import, export, and metapopulation dynamics will op­ timize fishery benefits for the many marine vertebrate and invertebrate species that possess pelagic larvae.

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