Form and Function of Sharks 33
How good is a shark’s sense of smell?
Elasmobranchs have exceedingly acute olfactory (smelling) capabilities,
which they use to find prey over long distances. Many popular accounts
refer to sharks as “swimming noses” because of their reliance on this sense.
Detection involves paired nostrils on the underside of the snout. The
nostrils lead to the enlarged olfactory bulbs of the brain via olfactory
nerves. A shark’s olfactory bulb takes up 3% to 14% of total brain mass,
depending on the species. White Sharks have the largest olfactory bulbs
relative to brain mass of any shark, skate, or ray. Hammerheads are inter-
mediate (7% of brain mass), and skates fall at the lower end, although they
are still remarkably sensitive to odors.
Sharks are attracted to blood, as we all know, but some other chemicals
are even more enticing. Laboratory tests have shown that certain amino
acids, the building blocks of proteins, are more stimulating than blood.
Amino acids would be released into the water when a fish or crab was in-
jured or decomposing, or even was just excreting waste products, which
happens more often than injury.
Olfactory cues can be dispersed in a number of ways. One is diffusion
of odor molecules through the water. But diffusion is a slow process that
may disperse odors a short distance, on the order of a few meters. Longer-
distance detection requires that the odor be carried by water currents, and
this is probably the major way sharks locate food using their sense of smell.
Operators of shark-watching boats attract White Sharks to the boats by
A single vertebra thought to be from
a White Shark. Several of these large
vertebrae were found on a beach at
Goose Island, British Columbia, and
are now on display at the Whale In-
terpretive Centre at Telegraph Cove
on Vancouver Island, British Colum-
bia. Photo by Gene Helfman