Foods and Feeding 139
muscles, lifting of the throat region, and additional contractions of the
stomach itself. The surrounding seawater then rinses away the rejected
items. Afterwards, the stomach is pulled back in through the mouth and
back into place by a combination of suction and peristaltic waves passing
down the esophagus. Such “gastric oral eversion” is known in several other
shark species. Expulsion of objects from the other end of the intestinal tract
is accomplished by pushing the intestine out through the cloaca. Between
gastric oral eversion and intestinal cloacal inversion, sharks would be able
to cleanse and flush their entire gastrointestinal tract. Dogfish may not
bark, but they can barf.
How do sharks find food?
Sharks use all five of their senses, plus one or even two we lack, to detect
and then home in on food items. Different senses function additively at
different but overlapping distances from a food source, increasing the ac-
curacy of detection as the shark closes in on the food.
Hearing and smell operate at the greatest distances and over different
time scales. Sound travels fast in water; chemicals diffuse slowly. Numerous
experiments have shown that sound alone attracts sharks to a potential food
source. Sharks detect sounds with their inner ears, much as we do. Pulsed
sounds between frequencies of 20 and 1100 Hz are especially attractive.
In the sea, these are the frequencies emitted by a rapidly swimming fish or
by the squeaks, squeals, grunts, thumps, and buzzes produced by injured
A general picture of the additive use
of the senses in foraging sharks.
Distances given are approximate
and change with water clarity, light
levels, prey type and behavior, cur-
rent speed, and habitat, not to men-
tion shark species. Under some
conditions, smell may function at a
greater distance than hearing. Illustra-
tion by Gene Helfman