Abstract

In the present study, acoustic telemetry was used to assess the movement and residency patterns of several shark species around artificial reefs in the northern Gulf of Mexico. Eight sandbar sharks (Carcharhinus plumbeus), five Atlantic sharpnose sharks (Rhizoprionodon terraenovae), four bull sharks (Carcharhinus leucas) and two nurse sharks (Ginglymostoma cirratum) were monitored within a 64 km2 area for periods of one to 450 days. Sandbar sharks had the highest overall residency indices (range = 0.004-0.432, mean±SD = 0.151±0.160) followed by nurse sharks (range = 0.02-0.10, mean±SD = 0.06±0.05), Atlantic sharpnose sharks (range = 0.001 – 0.049, mean±SD = 0.013±0.020) and bull sharks (range = 0.001 – 0.024, mean±SD = 0.012±0.010). Residency indices were not significantly different among species (F4,17 = 2.37, P = 0.09). Residency indices were significantly different among seasons for sandbar sharks (F3,65 = 3.81, P = 0.014), nurse sharks (F3,16 = 3.48, P=0.041) and bull sharks (F3,28 = 54.29, P < 0.001). Five individuals also made long- distance seasonal migrations: two sandbar sharks were detected off the coast of Florida and South Carolina (247 km - 1,888 km), one bull shark was detected in the Florida Keys (844 km) and one nurse shark was detected in the Florida Keys in two consecutive years (864 km - 866 km). Homing behaviors were apparent for some migrating individuals. For example, one sandbar shark returned to the same site after a 3,776 km round-trip migration, and one nurse shark emigrated and returned to the same sites over four consecutive years. The present study indicates that individual sandbar sharks can show both high site fidelity and long-distance migrations. Similarly, individual nurse sharks can also perform long-distance migrations that are greater than previously known.

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