Shark Behavior 79
is left to land. But some sharks have learned to follow wading anglers in an-
ticipation of the activity. This behavior has been observed in several places
in the Caribbean where anglers stalk Bonefish in shallow water, only to
find they are in turn being followed by large Lemon Sharks. Bonefish are
legendary for putting up a long and strenuous fight, after which the angler
usually releases the Bonefish. But the long fight often exhausts the Bone-
fish, making it vulnerable to nearby predators. One study estimated that as
many as 40% of released Bonefish are eaten by attendant Lemon Sharks.
Why do sharks swim at the surface with their dorsal
fins sticking out?Assuming we are talking about sharks in water deep enough to sub-
merge their entire body, no one really knows the answer. This behavior
certainly makes life easier for Hollywood filmmakers during dramatic, sus-
penseful moments, but that doesn’t help the sharks much. The key prob-
ably lies in thinking more in terms of why sharks swim near the surface,
which they certainly do more than many other large fishes. That their dor-
sal fins stick out is an artifact of having a stiff fin protruding from their back
more than a result of the shark actually trying to stick it out of the water.
One possibility is discussed in chapter 2 at the end of the section “How
good is a shark’s sense of smell?”
How smart are sharks?
In the several ways by which we measure intelligence—brain size,
learning ability, behavioral complexity, creativity, or insightful behavior—
we could be accused of stacking the deck in favor of humans, since we use
measures on which humans tend to score high. These metrics may not
necessarily be appropriate for assessing intelligence in other animals, espe-
cially sharks.
With those caveats in mind, scientists use two main types of information
to assess intelligence in sharks: brain size and learning ability. Brain size
has to be scaled relative to body size, because larger animals with bigger
heads can obviously have larger brains, period. Two measures are therefore
used, and argued about: brain weight relative to body weight, and the “en-
cephalization quotient,” a measure of brain size compared to an accepted
standard (admittedly a human standard) (see “How large is a shark’s brain?”
in chapter 2). For present purposes, the first measure of brain weight rela-
tive to body weight will do.
It is difficult to determine evolutionary trends in brain size among
elasmobranchs other than to say that groups that are more evolutionarily