Data for mangrove oyster (Crassostrea tulipa) spat collection in Gulf of Guinea brackish systems 2017-2018
Description
Wild harvests of the oyster (Crassostrea tulipa, Lamarck 1819) are threatened by adverse oceanographic conditions, and therefore, the species is under serious consideration for management and aquaculture production development. Towards this goal, experiments were wet up in different water bodies to explore strategies for optimal seed production. This data was collected to test two key hypotheses; 1) that there were no spatial and temporal variations in spat availability among and within different brackish systems along the Gulf of Guinea coast of West Africa, and 2) that artificial spat collectors did not differ in their efficiency for harvesting C. tulipa from the open water systems. Different spat collectors were deployed on stationary racks at three different locations in each of four different brackish systems namely, Densu Delta, Narkwa Lagoon, Bwnya Lagoon, and Whin Estuary. Five treatments of different oyster spat collector substrates (coconut shell, nylon net, oyster shell, PVC, and ceramic tiles) were deployed to evaluate their effectiveness for harvesting C. tulipa spat (response is spatfall; number of spat per sq m). Spat collection was repeated monthly for a year (12 months). Three experimental stations (ST) with bamboo racks mounted were established in each water body to cover the head, middle, and mouth regions. For each collector type, 9 collectors were deployed on three strings (i.e. three collectors per string) affixed to a rack at each experimental station. Hence, a total of 45 collectors were deployed per station and 540 for all the water bodies combined (12 stations). Later in the experiment, one station was eliminated due to the consistent destruction of the rack by local fishers. Sampling was done monthly by harvesting all collectors and replacing them with a new set each month. Collectors were examined in the laboratory for settled spat on them. The total number of spat on each collector was counted. For each collector unit deployed, spat settlement was recorded for both sides, that is, the upper- and lower-horizontal surfaces. Spatfall on individual collector surfaces and mean spatfall per sq m were calculated based on density. The monthly rainfall and anomalies in the vicinities of the four brackish systems were obtained from national meteorological data stations (Meteo Stations = Accra, Saltpond and Takoradi). Accra for Densu Estuary, Saltpond for Narkwa and Benya Lagoons, and Takoradi for Whin Estuary.