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What is the metabolism of a shark?
Sharks live in the slow lane. They have what we consider to be very slow
metabolisms and are built to conserve energy in almost all aspects of their
lives, especially when compared with us or even with bony fishes. Their
fins and scales and body shape, as discussed in questions in this chapter, are
optimal for moving through the water efficiently. In addition, their resting
metabolic rates are comparatively low, about one-third that of similar-sized
bony fish. Their active metabolic rates are only about 3 times that of rest-
ing rate, whereas in a bony fish, active rates are 10 times that of resting
rates. Feeding rates are also low: a 2-kg (4.5-lb) Spiny Dogfish, Squalus
acanthias, needs only 8 g (about a third of an ounce) of fish per day to main-
tain itself, whereas a similar-sized salmon needs four times that amount.
The above generalizations hold when we talk about small sharks such
as the Spiny Dogfish, which are about the size of some bony fishes. It is
considerably harder to measure the metabolism of large sharks because of
difficulties of keeping them in captivity. But indirect measures can be used,
such as estimating oxygen consumption by looking at body temperature as
a shark with a transmitter passes through water of different temperatures.
This was done for a 4.5-m-long (14.75-ft) White Shark. The resulting cal-
culation indicated that the White Shark used about one-eighth of the oxy-
gen per pound of body weight that a human being uses. The same calcula-
tions give us some idea of how often a White Shark must feed to maintain
itself. If the same shark fed on a dead whale and ate 30 kg (66 lb) of whale
blubber, which is not an unusual amount for a White Shark, it could sur-
vive for six weeks before it would have to feed again.Chapter 2
Form and Function
of Sharks