Behavioral Sensitivity of Adult Sandbar Sharks, Carcharhinus Plumbeus, to Prey-Simulating Electric Fields

Elasmobranchs detect weak electrical stimuli in their environment using specialized organs called ampullae of Lorenzini, found at the base of conductive jelly-filled canals that terminate as pores on the surface of the skin. Pore numbers do not change through ontogeny, so adult animals have lower pore densities than juveniles. This is hypothesized to result in decreased resolution. The canals, however, lengthen with ontogeny, which is hypothesized to increase sensitivity. Previous elasmobranch electrosensitivity studies have been limited to small animals, primarily juveniles and neonates. We used a behavioral assay to quantify the sensitivity of large adult sandbar sharks (Carcharhinus plumbeus, mean total length 183cm) to prey-simulating electric fields. The results of this experiment were compared with previously published data on juvenile sandbar sharks (mean total length 69cm) to evaluate the effects of ontogeny on sensitivity. Adult sandbar sharks demonstrated a lower median sensitivity, 0.002 nV/cm, than juveniles, 0.5nV/cm. The minimum field that elicited a response in adults was also lower, 1.156 nV/cm, compared with 25.2nV/cm in juveniles. This is the lowest documented sensitivity of any elasmobranch to date. Our results support the hypothesis that canal lengthening through ontogeny results in increased electrical sensitivity in larger animals.