The spatiotemporal dynamics of habitat use by blacktip (Carcharhinus limbatus) and lemon (Negaprion brevirostris) sharks in nurseries of St. John, United States Virgin Islands

摘要

Shark nursery areas are widely regarded as essential habitats for the growth and survival of young individuals. The effective management and protection of shark nursery habitat are contingent upon a clear understanding of how individual species utilize such habitat both spatially and temporally. Although shark nurseries have been identified in the Caribbean, this information is generally lacking. From 2006 to 2012, we used passive acoustic telemetry to monitor the presence, movements, and habitat use of 65 juvenile blacktip sharks (Carcharhinus limbatus) and 42 juvenile lemon sharks (Negaprion brevirostris) within Fish Bay and Coral Bay, two shark nurseries in St. John, United States Virgin Islands. Both species were present in each bay during all months of the year, but abundance peaked during the summer (June-September). Although telemetry data indicated that blacktip and lemon sharks moved throughout each embayment, each species exhibited strong site fidelity to core areas across all years of the study. Habitat partitioning was observed in both nurseries as blacktip sharks generally occurred in areas characterized by water depths of 1.5-6 m with seagrass and sand/mud substrate, while lemon sharks remained in close proximity to or within shallow (＜1 m), mangrove-fringed seagrass habitat. Blacktip sharks were also observed to exhibit greater activity space during the nighttime hours (1900-0659 h) within Coral Bay. The results of this study indicate that Fish Bay and Coral Bay are nursery areas that warrant designation as essential fish habitat and exemplify the need for additional focused management measures.