Spatial and size distribution of Queen Conch (Lobatus gigas) veligers in relation with ocean surface currents in Lac Bay, Bonaire

Since the 1970s the demand for Queen Conch (Lobatus gigas) meat increased due to the growth of tourism. This resulted in the collapse of the fisheries on this species and in CITES taking the species up in their Appendix II. Despite the various regulations little recovery was noticed. Fishery on the Queen Conch in Bonaire has been reduced since the 1930s and is prohibited in the present. Even though there are regulations against fishing, poachers still harvest this species. One of the problems, next to overfishing, is that harvested conchs get younger every year. Because veligers of the Queen Conch do not actively swim they are dependent on ocean currents for their dispersal. It is hereby that veligers can be transported for hundreds of kilometres resulting in the possible dependency of the Queen Conch population of Lac Bay on distant larval sources. Bonaire is located in downstream currents from Los Roques, Venezuela. Therefore there is a possibility that the majority of Bonaire’s Conch population may originate from sources in that direction. So where do veligers in Lac Bay come from? How many are present? Where are the veligers located? And what is the influence of ocean currents on their dispersal? Plankton was collected by using a conical plankton net with a mesh size of 200μm and with a diameter of 0.5m. Samples were taken at the surface. After towing samples were fixated by either a 4% formaldehyde-seawater solution or a 96% ethanol solution. Veligers were located and identified microscopically. Before identification took place veligers were divided in four size classes: 200-300 μm, 300- 600μm, 600-900 μm, and >900 μm to help determine their origin. However, identification was difficult therefore an additional group was introduced: the cf. veligers. Additionally the direction of the surface currents and the flow of currents below the direct surface of Lac Bay were determined. The plankton samples that were taken in Lac Bay provided data on the occurrence of Queen Conch veligers and their spatial and size distribution throughout the bay and in the direction of Las Aves Archipelago. Surface currents data provided insights in the velocity and direction of currents that ran through the bay. Veligers found during this study ranged from 0.0 to 0.00035 individuals per litre. Veligers in the smallest size classes were most abundant, which could mean that the source of the veligers is in the close vicinity of Lac Bay. Additionally, veligers were more abundant around the reef possibly due to the fact that Queen Conch forms spawning aggregations near reef tracts, in addition phototaxis might have played a role. What the effect is of currents on the dispersal of Queen Conch veligers has to be further determined by performing more research. 

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