Schooling in Sphyrna lewini, a Species with Low Risk of Predation: a Non-egalitarian State

Authors

  • Dr. A. Peter Klimley

    Corresponding author
    1. Marine Biology Research Division (A-002), Scripps Institution of Oceanography, University of California, San Diego, La Jolla
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Marine Biology Research Division (A-002), University of California, San Diego, La Jolla, CA 92093, U.S.A.

Abstract

The scalloped hammerhead, Sphyrna lewini, forms schools as highly polarized as those of the obligate schoolers, Atherinops affinis, Engraulis mordax, Scomber japonicus, and Trachurus symmetricus. On the other hand, schooling hammerheads do not maintain preferential elevations and bearings to their nearest-neighbors and remain at larger inter-individual distances than the facultative schoolers, Gadus morhua and Pollachius virens, and the obligate schooler, Clupea harengus. Members of hammerhead schools vary in size more than those of small bony fishes. Furthermore, aggression is very common in schools of hammerheads; most individuals are females which compete for a position at the center of the school. Larger females perform two approach-type behaviors, Hit and Cork-screw, within the schools and force smaller sharks to the edge as they perform two withdrawal-type behaviors, Acceleration and Head-shake. Males are rare and enter the schools, performing Torso-thrust. The differences between schools of hammerheads and those of small teleosts are consistent with schooling in hammerheads functioning not to confer protection from predation, but to permit conspecifics to interact socially during the resting phase of their diel cycle.

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