Energy absorption from ocean waves: a free ride for cetaceans.

Flukes of cetaceans are capable of absorbing energy from ocean waves for propulsion. The extent of this energy absorption is demonstrated by considering the flukes of an immature fin whale, Balaenoptera physalus. In a fully developed seaway corresponding to a wind speed of 20 knots (around Beaufort force 5) and at a low swimming speed, of 2.5 m s-1, this whale was able to absorb up to 25% of its required propulsive power in head seas and 33% of propulsive power in following seas. Consequences of wave-energy absorption for energetics of cetacean migrations are discussed.