Satellite tracking of whale sharks using tethered tags

Aggregations of whale sharks, Rhincodon typus, occur each year off South Africa (Indian Ocean) and in the waters surrounding Utila, Bay Islands, Honduras (Caribbean Sea), where they form the basis of a whale shark ecotourism industry. In 1998 and 1999 the Shark Research Institute deployed tethered satellite tags on five whale sharks in an effort to gather information on their diving profiles and both long-term and short-term movements. Satellite tags were attached to the sharks by divers using tag anchors placed in either the skin or musculature of the shark, and tethers from 1.5 to 7 m were used with varying degrees of success. Tethered tags provide real-time data about the habitat use and diving profiles of whale sharks, and may be recovered if they detach prematurely from the host animals. An unexpected finding was that the sharks dived regularly to depths of >320 m, which may have contributed to premature detachment of the tags due to drag and, as result, the hydrodynamics of the tag were refined. Sharks tagged off the coast of KwaZulu-Natal, South Africa, travelled northwards. One shark tagged off the coast of Utila Bay Islands, Honduras, travelled to the Swan Islands, then moved along the Yucatan Peninsula and into the Mexico Basin, while the second shark tagged off Utila travelled to the coast of Belize. This study confirms that tethered satellite tags are effective tools in monitoring travel paths and habitat use of whale sharks when real-time data is needed.