Home range and diving behaviour of Heaviside’s dolphins monitored by satellite off the west coast of South Africa

Abstract

Three Heaviside’s dolphins Cephalorhynchus heavisidii were fitted with satellite depth recorders off the west coast of South Africa during February–April 1997 and monitored for 51, 73 and 130 days, respectively. In total, 345 locations were received from the three animals, but only 27 from one male. Using α -local convex hull and minimum convex polygon methods, respectively, the home range for the remaining male was estimated at 1 520 and 2 347 km², with corresponding core-area estimates (50% of locations) of 134 and 123 km². For the female, the home range estimates were 672 and 1 027 km², and those for the core area were 71 and 230 km². The female’s home range was the smallest yet described for this species, and the animal was resighted nearly three years later within 13 km of the tagging site. Binned dive data were received at 6-hourly intervals. From comparison of maximum dive depth and time-at-depth data, we concluded that dives <4 m deep were associated with surfacing bouts. Dives to below 4 m occurred throughout 24 h but were shallower during the day and deepest either at dusk or at night. This pattern was consistent with earlier descriptions of offshore movement during the day and may be related to the diel vertical migration of its principal prey, shallow-water hake Merluccius capensis.

Keywords: Cephalorhynchus heavisidii, dive depth, saddle attachment, Service Argos satellite system, surfacing intervals, time-at-depth

African Journal of Marine Science 2014, 36(4): 455–466