Further evidence of the importance of St. Helena as habitat for whale sharks

Abstract

Background Remote oceanic islands may play important roles in the life history of whale sharks; they have been hypothesized to be the site of mating or pupping in this species. One such island is St. Helena in the South Atlantic, which was recently discovered to play host to a seasonal population of adult male and female whale sharks. Approach Two collaborative expeditions have been conducted to St. Helena since the 3rd International Whale Shark Conference. The goals of these were: to document whale shark abundance and population composition, to characterise behaviour and habitat use around the island, and to determine regional scale movement patterns using satellite telemetry. Results The whale shark population observed at St. Helena consisted of an approximately equal mix of mature males and females. The animals were 8.5–11 m in length, i.e. larger than the sub-adults seen in most coastal aggregation sites, but smaller than the large female animals seen regularly in the Galapagos. Two reliable eyewitness accounts of mating behaviour have been recorded at St. Helena, but we have not directly observed this behaviour during the expeditions. An acoustic array was deployed around the island in January 2016 to determine local habitat use patterns, but data are not expected to be available from this effort until the end of 2016. Conclusions Preliminary satellite telemetry results suggest that St. Helena whale sharks travel to the west coast of Africa, not to the east coast of South America. We propose that regional movement patterns are similar to those observed in the eastern Pacific, with animals apparently feeding in coastal upwelling zones, and travelling to remote oceanic islands to fulfill aspects of the reproductive cycle. Environmental regulations have recently come into effect that completely protect the whale shark in waters surrounding St. Helena.