Rosemary Gales A , Rachael Alderman A B , Sam Thalmann A and Kris Carlyon A

Abstract

Context: Mass strandings of cetaceans occur frequently in Tasmania, Australia, with efforts made by authorities to rescue stranded animals when possible. Determining the fate of rescued cetaceans following a stranding event is essential to assess individual survival and the effectiveness of rescue procedures; however, few studies have monitored animals post-release and their fate remains largely unknown. Satellite telemetry of released cetaceans provides a means of assessing the short- to medium-term success of stranding management techniques.

Aims: To examine the short- to medium-term survival and at-sea movement and behaviour of long-finned pilot whales (Globicephala melas) on their release following a mass-stranding event.

Methods: We deployed satellite transmitters on 5 of 11 long-finned pilot whales returned to sea after a mass-stranding event in Tasmania in November 2008. The transmitters, incorporating a corrosive link, were attached to the dorsal fin of two adult and three subadult whales before release. The resulting telemetry data were examined to infer behaviour of the tagged individuals post-release, including swim speeds and how individuals moved in relation to each other over time.

Key results: Tracking data established the success of the rescue attempt and confirmed survival of stranded individuals in the short term (12–32 days) following release. Although conditions required whales to be released individually, data showed the tracked whales re-united immediately after release. A subsequent aerial survey revealed that they had formed a larger group with six additional whales which then separated and reformed.

Conclusions: Short-term survival of long-finned pilot whales following mass stranding and rescue was confirmed and behaviour was consistent with known behavioural information for this species. Importantly, the present study demonstrated physical recovery from a traumatic event in spite of delayed rescue and that individuals successfully re-united following individual release.

Implications: The present study confirmed that the rescue procedures employed were successful in the management and release of mass-stranded long-finned pilot whales, at least in the short term. It also provided some insight into the at-sea behaviour of this highly social and gregarious species and supported the theory behind stranding management techniques and the considerable resources and effort required for rescue of stranded cetaceans.