Do basking sharks hibernate?
Until recently it was thought that basking sharks hibernate in the winter. There were two main reasons for this hypothesis. The first reason was that basking sharks apparently disappeared for most of the year. People normally see them in the late spring and summer. Sightings at other times of year are very much rarer. There has been one sighting of a basking shark off the west coast of the Isle of Man this February (2005) so winter sightings are not unknown, just rare. The second major reason for thinking that basking sharks hibernate was that some winter-caught basking sharks have shed their gill rakers. This obviously renders them incapable of filter feeding. This led to the general belief that basking sharks probably hibernate on the bottom in deep water whilst their rakers grow back and until the plankton levels came back to levels that made it worthwhile for them to feed. It was thought that they lived off the huge store of oil in their liver. A 4-ton basking shark may have a one