Sharks The Animal Answer Guide

Foods and Feeding 155

surround it, and progressively tighten the circle. Escape attempts by the

seal are thwarted by individual sharks that refrain from attacking it but

force it back to the center of the tightening circle. Eventually, one or more

Sevengills actually bite the seal, which stimulates attacks by the rest of the

pack. Sevengills are also thought to use cooperative feeding to eat other

large prey such as large Bat Rays, Spotted Gully Sharks (Triakis megalop-

terus), porpoises, and other Sevengill Sharks. All of the elements of cooper-

ative feeding were observed in the reported attacks, including coordinated

movement, division of labor, and initial restraint.

Other sharks that are thought to feed cooperatively include Sand Tigers

off North Carolina and Australia, and Blacktip Reef Sharks in the Indo-

Pacific. Sand Tigers have been observed herding prey, usually schooling

fishes. In the waters off North Carolina, a school of 100 or more Sand

Tigers, a species that is usually solitary, surrounded a school of Bluefish

(Pomatomus saltatrix) and herded them into very shallow water, shallower

than Bluefish and Sand Tigers normally occupy. The sharks then launched

an all-out attack on the nearly stranded Bluefish. A group of Sand Tigers

off New South Wales, Australia (where they are called Gray Nurse Sharks),

herded a small shoal of juvenile Yellowtail Kingfish (Seriola lalandi) into

a tight group before feeding on them. These sharks herded the prey by

whipping their tails and creating sharp pressure waves that sounded like

gunshots. The tail whipping may also have stunned the prey fish; killer

whales also use this technique to feed on herring in the waters near Iceland.

Broadnose Sevengill Sharks feed cooperatively on fur seals. (a) The sharks first form a loose circle around the prey and
(b) then tighten the circle and prevent any attempts at escape; (c) eventually one shark launches an attack, at which
time (d) the rest of the group shares in the kill. From D. A. Ebert, “Observations on the predatory behaviour of the Sevengill Shark Noto-
rhynchus cepedianus,” South African Journal of Marine Science 11 ( 1991 ): 455 – 65 ; reproduced with permission, © NISC (Pty) Ltd