Habitat Use of Blacktip Sharks (Carcharhinus limbatus ) at Fishing Piers

摘要

Blacktip sharks (Carcharhinus limbatus) can be observed near fishing piers throughout the summer along the northeast coast of South Carolina. These piers attract and support a wide variety of potential prey and sharks are able to forage on fishers' discards with minimal energetic cost. I tagged 12 blacktip sharks with acoustic transmitters, monitored piers with acoustic receivers, and conducted pier-creel surveys to determine the habitat use of blacktip sharks at fishing piers, factors that influenced residence time and presence/absence at piers, and any cyclical patterns in visits to piers. Data were analyzed with pier association indices (PAI), mixed models, and fast Fourier transformation analyses. While the majority of monitored sharks were infrequently detected at piers, four (33.3%) displayed a high degree of fidelity at piers. Two sharks (16.7%) were detected only at the pier where they were tagged, whereas two other individuals were detected at all monitored piers in 2017. The most likely model for shark residence time at piers included terms for pier location and diel cycle (wi = 0.52), while the most likely model explaining presence/absence of sharks at piers included terms for tidal height and diel cycle ( wi = 0.95). Sharks did not display cyclical patterns in detections at piers. To my knowledge, this is the first study to specifically examine the habitat use of blacktip sharks at fishing piers. My data suggests that fidelity of sharks at piers is a phenomenon for some of the tagged sharks, but not all.