Foods and Feeding 145
Nearly half of the 33 sharks filmed struck at the bait with their tail, hitting
the bait 65% of the time. Six sharks struck more than once; one individual
struck at the bait seven times in less than a minute. An average strike lasted
two-tenths of a second, the shark striking the bait about midway down its
tail. None of the sharks tried to bite at the bait before striking it with its
tail. Other researchers filmed Pelagic Thresher Sharks (Alopias pelagicus)
near the Philippines feeding on schools of sardines. A shark would rapidly
enter a school of prey, brake with its pectoral fins, and sling its tail tip over
its head, literally whipping the tip at the sardines. The tip can reach speeds
of 129 kph (80 mph) and injured the prey, sometimes breaking their spines
and even cutting them into pieces. The disabled prey were then swallowed.
These observations clearly show that tail strikes are a common and even
preferred feeding tactic, at least in these species.
Ambushers. Ambush predators are frequently referred to as “lie-in-
wait” foragers, evoking the image of a lioness hiding in tall grass and
pouncing on a passing zebra or tourist. Sharks and their relatives seldom
have the convenience of tall grass to hide in. Instead, they either move
slowly through the water, sneaking up on prey, which they capture with a
sudden burst of speed, or they lie partially or completely buried in bottom
sediments, lunging out at passing fish and crustaceans. The element of sur-
prise is key to success in ambush predators.
Some of the largest sharks, including White Sharks and Tiger Sharks,
are ambush predators of the first type. White Sharks have been extensively
photographed launching themselves up into the air, a squirming young
Cape fur seal tightly grasped in the deadly jaws. A typical feeding sequence
near Seal Island, South Africa, begins shortly after dawn, with the shark
moving slowly near the bottom. Its dark back blends with the dark bottom
below, the camouflage enhanced by the dim light conditions of early morn-
ing. Upon detecting the silhouette of an unsuspecting seal at the surface,
the shark explodes to the surface, snapping its jaws closed as it engulfs the
seal. The surface rush has been named the “Polaris breach” because it is
reminiscent of a Polaris missile being fired upward from a submarine. The
success rate of initial breaches and lunges observed at Seal Island was about
31% and declined rapidly if the seal escaped the initial attack; fewer than
20% of feeding sequences involving multiple capture attempts were suc-
cessful. (Some individual sharks, however, are successful as much as 80% of
the time, and White Shark attacks on sea lions off the Farallon Islands near
San Francisco are successful 99% of the time.) Once the shark loses the
element of surprise, the likelihood of success plummets. An average attack
event is over in less than a minute and a half.
Tiger sharks feed on all sorts of active prey, including dolphins, sea tur-