When sharks just open wide and say yum.

Basking sharks may not be living on the knife-edge of starvation after all.

Watching sharks and modeling their energy use has convinced David W. Sims of the University of Aberdeen in Scotland that the animals get by quite well with less than half the prey density that researchers believed sharks need. In the July 22 PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON B, Sims releases more results of an ongoing project that's challenging 40 years' thinking about sharks.

Basking sharks feed by stretching open their jaws and barreling through clouds of little water creatures such as copepods. Bristle-like rakers near the sharks' gills filter out the good stuff. The method may yield a decent dinner, but it's hardly an efficient way to swim. Old calculations suggested that the sharks need a food density of at least 1.4 grams per cubic meter (g/[m.sup.3]).

However, Sims found that basking sharks in the English Channel routinely dined until food patches thinned out to 0.5 to 0.6 g/[m.sup.3]. Those numbers agree with conclusions from a feeding model that Sims updated to include such factors as modern measurements of shark metabolism and swimming.

The numbers undermine the old theory that skimpy prey drives the sharks into hibernation, Sims says. He doubts that they hibernate at all.