Population Assessment of Queen Conch, Strombus gigas, in the St. Eustatius Marine Park, Netherlands Antilles

Abstract:

Queen Conch, Lobatus gigas, is a large, herbivorous, marine gastropod found primarily in the Western Atlantic Caribbean region. Adult conch range in length anywhere from 143-264 mm and are typically found in depths up to 25 meters, but are more often found between 10 – 18 meters. Due to its commercial importance and high market value, queen conch populations have dwindled to extremely low levels within its range. St. Eustatius Marine Park was established in 1996 and became actively managed in 1998 to conserve and protect the marine environment surrounding St. Eustatius up to and including the 30-meter (100 feet) depth contour and regulates the conch fishery on the island. Within the park, two no-take reserves are established on both the northern and southern ends of the island. The study revealed numerous sites that are ideal conch habitat from depths of 60-110 feet. Average density of conch was 0.043 conch/m2. A total of 86 individuals were included in the survey. The average length of conch was 22.1 cm with average lip thickness was 1.0cm. Individuals were on average 170.4 cm apart and were uniformly distributed. Density of Lobatus gigas in St. Eustatius is three times greater than densities reported for Turks and Caicos but drastically lower than densities reported for beds at similar depths in the Bahamas and Dominican Republic. The results of this survey suggest that Statia’s conch population may be very unique because the shallowest bed is located at 60 feet and conchs have been observed in depths up to 110 feet. Conch may be aggregating in certain areas for nutritional, reproductive or protective benefits. Typical locomotory and reproductive behaviour were observed during the study. Most conch surveyed met regulation size, which is encouraging because it means that juveniles are being left and allowed to reach sexual maturity thereby replenishing the population. Because catches are not reported it is not known if most conchs being collected are greater than 19cm (siphonal length) and have a fully-grown lip, which may mean immature individuals may be being removed prior to reproducing. There are numerous opportunities for further study on the L. gigas population in the St. Eustatius Marine Park including larval, behavioural and migration studies as well as collection of basic oceanographic data, which would have widespread applicability.