Blacktip shark Carcharhinus limbatus presence at fishing piers in South Carolina: association and environmental drivers.

Abstract

We tagged 12 Carcharhinus limbatus with acoustic transmitters and monitored their presence at five piers along the north-east coast of South Carolina, USA in 2016 and four piers in 2017 using acoustic receivers. Data were analysed with pier association indices (PAI), mixed models and fast Fourier transformation analyses to identify potential factors related to residence time and presence at piers and any cyclical patterns in visits to piers. While the majority of monitored C. limbatus were infrequently detected at piers, three (25.0%) were highly associated with piers (PAI ≥ 0.50). Of the C. limbatus that were detected after initial capture, three (25.0%) recorded detection events only at the pier where they were tagged and two individuals (16.7%) recorded at least one detection event at all monitored piers. The best-fit model explaining C. limbatus residence time at piers included terms for pier location and diel cycle (wi = 0.88), whereas the best fit model explaining presence-absence of C. limbatus at piers included terms for tidal height, diel cycle, barometric pressure and angler count (wi = 0.98). Carcharhinus limbatus did not appear to display cyclical patterns in their visits to piers. Along the north-east coast of South Carolina, association of C. limbatus with piers is a phenomenon for a proportion of mature individuals, but continued research is necessary to understand if this behaviour is driven by attraction to and feeding on angler discards or increased foraging opportunities resulting from the attraction of potential prey to the physical structure provided by piers.