156 Sharks: The Animal Answer Guide
This tail whip-cracking has been reported as a defensive behavior by the
same shark in South Africa when cornered by divers in a cave (see “Are any
sharks territorial?” in chapter 4).
Blacktip Reef Sharks near Palau, Western Caroline Islands, have been
observed at least twice feeding perhaps cooperatively. Three Blacktips
swam along a shoreline, “escorting” a school of 15 to 20 Milkfish (Chanos
chanos). The sharks appeared to be keeping the Milkfish from moving into
very shallow water by cutting off their access to the shoreline, while forc-
ing them into a tight group. Different sharks intercepted the school if it
moved into shallower water. The sharks’ movement was slow except when
individuals cut off the compacted Milkfish school if it moved toward the
shore. No attacks occurred. The Milkfish school then swam into deeper
water with the sharks following closely. On a second occasion, the same ob-
server watched seven juvenile Blacktips that kept a group of about 20 small
jacks (Caranx sexfasciatus) bottled up against the roots of a small mangrove
islet. The Blacktips formed a semicircle, individuals occasionally darting
towards the mangrove roots to attack any jacks that strayed beyond the
mangrove plants. The observer speared one of the sharks and found a par-
tially eaten jack in its stomach.
Other species of sharks (Oceanic Whitetip, Whitetip Reef, threshers)
have been observed and reported as possible cooperative feeders, but the
observations remain unconfirmed. Recognizing that sharks have relatively
large brains, and that our knowledge of the catalogue of their behaviors
grows in complexity with the years, it won’t be surprising to learn that
other species feed in a coordinated, cooperative manner.
http://www.ebook3000.com