Comparison of Homing Patterns of Strombus gigas and Strombus costatus in Greater Lameshur Bay

Moreau, Carine

ABSTRACT: In Greater Lameshur Bay there are two populations of the conch strombus, Strombus gigas and strombus costatus. The daily movements of five representatives of each species were followed for six consecutive days to monitor the possibility of a homing instinct. It was found that the conch were significantly (p<.05) moving towards their home. The S. gigas moved eastward and the S. costatus moved westward. INTRODUCTION: The queen conch, Strombus gigas, and the milk conch, strombus costatus are two species of large marine gastropods found throughout the Caribbean. Both conch have similar life cycles, breeding patterns, and diets consisting of epiphytes scraped off of seagrasses and macroalgae(Webb 1985). The genus Strombus moves over the bottom in a very unique "pole vaulting" fashion. It uses its foot and claw-like operculum to dig into the sand and propel itself forward in a hop. Both species are found in abundance in Greater Lameshur Bay, St. John. In recent years the population of S. gigas has been threatened by overharvesting throughout the Caribbean. S. gigas has been harvested as an important food source for Caribbean people as well as for its beautiful pink shell. There is currently a five year moratorium to protect S. gigas in St. John and St. Thomas. This law forbids any collection of the queen conch until December 31, 1992. The purpose of the moratorium is to allow the population to regenerate. However, this five year protection will have no long-term benefit unless research is done to find out how to properly manage the harvesting of conch once the moratorium is lifted. Studies have been conducted on the habitat selection, reproduction, feeding, distribution, and migration of S. gigas. Not as much research has been done on Strombus costatus because it has only minor economic importance. Only recently has its life cycle been analyzed. S. gigas inhabits the shallower areas of the grass beds that are densely populated by the sea grass Thalassia testudinum, while S. costatus are found in deeper, sandier areas of the bay (Apledoorn 1985). The purpose of my project was to compare and contrast the daily roaming patterns of the queen conch Strombus gigas and the milk conch Strombus costatus. Five queen conch were taken from a grassy area to a sandy area and five milk conch were taken from a sandy area to a grassy area. The null hypothesis was that the movement of the conch would be random although they had been moved from their homes. By better understanding the homing patterns of these two conch species in Greater Lameshur Bay, it may be possible to set up protective areas to save the populations from extinction once the moratorium is lifted.