A historical approach to describing the complex behaviour of a large species of carnivorous shark. Case study No. 1: the scalloped hammerhead, Sphyrna lewini

Abstract

A historical example, case study No. 1, is given illustrating the complexity of interactions between sharks in their natural environment. Scalloped hammerhead sharks, Sphyrna lewini, form polarized schools at offshore islands and seamounts. Females perform a display while inside a school to force smaller individuals to the periphery. The Corkscrew consists of a rapid burst of swimming into a tight looping trajectory, with the shark rotating its torso almost 360° on its longitudinal axis. This conveys a shark’s intent to contact the recipient with a Hit. This is competition for a position at the centre of the school. Males dash into the schools, directing emphatic tail beats to one side with a Torso Thrust, propelling the shark‘s anterior torso laterally, to pair with a dominant female. The pair then moves outside the school to copulate in midwater with the male biting the female’s body and inserting his clasper within her uterus.