Initial Queen Conch (Strombus gigas) studies on St. Eustatius

The large marine gastropod, Queen conch (Strombus gigas) was studied over a period of 3 months on the island of St. Eustatius. Strombus gigas are widely distributed throughout the Caribbean and are important to local communities due to its nutritional and traditional value. Because of an increase in conch landings since the seventies Strombus gigas populations have dramatically declined causing it to be included in the Appendix II of CITES. Fishermen on St. Eustatius have seen Strombus gigas populations move to deeper waters. Strombus gigas have been actively protected since 1996 by the St. Eustatius Marine Park in all surrounding water up to a 30-meter depth contour; no fishing is allowed in the two marine reserves and regulations state that Strombus gigas may only be caught free diving to a max of 20 conch per person per year and with a minimum shell length of 19 cm. This study focuses on estimating a trend in Strombus gigas populations and testing a towed video method for benthic (queen conch) surveys. Dive surveys covered a transect of 50 meters long and 10 meter wide, noting species, shell length and lip thickness. The video array was constructed of light weight materials with a live feed to the towing vessel to check alignment. Towed video transects covered a length of 500 meters with a width of 1 meter only noting species and numbers. To calibrate this towed video method, a diver followed the video array on 5 occasions to establish a correction factor. Fisheries samples were taken whenever the fishermen would land his catches and notify us. Population trend surveys showed no clear trend and were unusable due to the limited sample size. For the dive surveys a total of 25 sites were sampled of which 11 sites met the minimum density for Strombus gigas to reproduce, of these 11 sites at least 5 are within the marine reserve and thus unfished. Towed video calibration proved promising, in the future better observer training and greater sample size is necessary. Of the 11 towed video sites, Strombus gigas clearly prefers the rubble/algae sites over bare sandy sites. Of the 11, 7 sites met the minimum required density for reproduction. But the towed video calibration made clear that the Strombus gigas numbers noted during the towed video analysis are likely to be an over estimate as adult Strombus gigas numbers seem to include dead Strombus gigas and Strombus costatus who are misinterpreted. In future studies better observer training is necessary, a larger sample size for trend indications and the towed video calibration is needed as well. Strombus gigas reproduction and fishing pressure also need to be studied. 

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