Influence of Ecosystem Components on Queen Conch (Strombus gigas) Population Densities in St. Croix, U. S. Virgin Islands

The queen conch is one of the most highly valued fishery resources throughout the Caribbean, but populations throughout its range have declined severely, and available data are insufficient for conducting traditional stock assessments.  To address this deficiency, we conducted stratified fishery-independent surveys of queen conch in St. Croix, U.S. Virgin Islands, generating habitat-based density data.  We completed 503 radial surveys and located 4773 individuals, representing a cumulative density of 302 conch per hectare.  Regression tree analyses were used to identify relationships between conch densities and measured ecosystem variables.  Habitat type was the strongest predictor of juvenile densities, followed by management zone and water depth.  The model predicted that the highest densities of juveniles would be found in patchy (30-50% cover) and continuous seagrass within the closed fishing zone in 11-15 m of water (2178 per hectare).  Adult densities were predicted to be highest (523 per hectare) across several different habitat types, at depths between 21-30 m within the closed fishing area.  This method of extrapolating population densities incorporating multiple ecosystem components can provide standing stock estimates for stock assessments.