Site fidelity of migratory bonnethead sharks Sphyrna tiburo (L. 1758) to specific estuaries in South Carolina, USA

Abstract

To examine the migratory patterns, habitat utilization and residency of bonnethead sharks (Sphyrna tiburo (L. 1758)) in estuarine systems within coastal South Carolina, a tag-recapture experiment was conducted from 1998 to 2012 during which 2300 individuals were tagged. To assess the intra and inter-annual movements of tagged sharks, six estuaries within state waters were monitored using multiple gear types in addition to the cooperative efforts of recreational anglers throughout the southeastern United States. Over the course of the experiment 177 bonnetheads were recaptured after 3days to 8.9years at liberty, representing a recapture rate of approximately 8%. All bonnetheads were recaptured within the same estuary where they were originally tagged on intra and/or inter-annual scales, with the exception of six individuals, which were recaptured during migratory periods (i.e. late fall, winter and spring) in coastal waters off Florida, Georgia, North Carolina, and South Carolina. On 23 occasions cohesion was demonstrated by groups ranging in size from 2 to 5 individuals that were tagged together and recaptured together, with times at liberty ranging from 12days to 3.6years. Additionally, 13 individuals were recaptured multiple times with times at liberty ranging from 12days to 8.9years; all individuals were recaptured in the same estuary where they were initially tagged. We hypothesize that bonnetheads are using South Carolina's estuaries as summer feeding grounds due to the relatively high abundance of blue crabs (Callinectes sapidus), including ovigerous females during spring and summer months, and the location of these ephemeral yet predictable feeding areas is socially transmitted to relatively young, naïve sharks by experienced, older individuals. The high degree of intra and inter-annual site fidelity demonstrated by bonnetheads in this region offers unique opportunities for in situ study of various aspects of the biology of this species, including identification of essential habitats, growth, homing mechanisms, mortality rates, movement patterns and social behavior.