Age Distribution and Density Patterns of Strombus gigas in Greater Lameshur Bay, Saint John, U.S. Virgin Islands

Conway, Sybil; Morrow, Tracey

ABSTRACT: In this study the population of S. gigas in Greater Lameshur Bay was surveyed, using band transects in star formations, to determine age-density patterns. We found two distinct size classes of juveniles (3.5 - 6 inches and 6 - 9 inches) which correspond to two year classes. The density of small juveniles was greater at the NW portion of the bed where the sea grass is less dense and there was a concentration of large juveniles at the SE end of the bed which is closer to the shore and where the growth of sea grass is more dense. INTRODUCTION: The Queen Conch, Strpmbus gigas, is found from Bermuda and South Florida throughout the Caribbean. For years this large marine gastropod has been prized for its beautiful shell and tasty meat. However, since the 1960’s its numbers have been declining due to overfishing. In order to maintain the conch population, in the face of rising demand for its products, management measures, such as size limits, catch quotas, and closed seasons, have been instituted. To make these management techniques more effective in meeting the needs of the conch as well as the people who depend on the income from conch fishing, further research into the population ecology of S. gigas is necessary. S. gigas can be found at depths ranging from 0 - 120 ft. (Berg). This range may correspond to the depth of the photic zone as S. gigas is an herbivore. Juvenile conch, 3 - 9 inches, are most abundant at shallower depths (30 -40ft.) (Randall, 1964). Thalassia testudinum and Syringodium filiforme beds are the favored habitat, but gigas is also found on sand flats, gravel, coral rubble, and hard coral rock bottom. (Randall, 1964). S. gigas grazes on epiphytic algae and bacteria found on the sea grass leaves and other substrates. S. gigas spawns once a year, from May to September, and adults migrate to shallow areas to lay eggs , usually between July and October (Berg). The S. gigas population in Greater Lameshur Bay was chosen for study because of its location within the Virgin Islands National Park. Although this population had experienced some fishing pressure in the past, it has been virtually untouched for the past year. The purpose of this study is to determine the location and size of the S. gigas population and to examine density patterns and age distribution.