Scaling of bite force in the blacktip shark Carcharhinus limbatus

Abstract

Although bite force is a frequently studied performance measure of feeding ecology, changes in bite force over ontogeny have rarely been investigated. Biting by the blacktip shark Carcharhinus limbatus was theoretically modeled over ontogeny to investigate the scaling of bite force, the morphological basis of the observed scaling relationship, the ecological consequences of ontogenetic changes in performance, and whether cranial morphometrics can be used as an accurate proxy for bite force. Theoretical bite force, which was positively allometric with respect to total length (TL), ranged from 32 N (61 cm TL) to 423 N (152 cm TL) at the anterior tips of the jaws and from 107 (61 cm TL) to 1083 N (152 cm TL) at the posterior teeth. This observation is attributed to positive allometry in the mechanical advantage of the jaw-adducting mechanism and the cross-sectional area of all four jaw-adducting muscles. Theoretical bite force was accurately predicted by cranial morphometrics including prebranchial length and head width as well. Although positive allometry of bite force in C. limbatus would seem to indicate an ecological necessity for this phenomenon, dietary analyses do not necessarily indicate any ontogenetic shift in prey types requiring larger bite forces. The positively allometric increase in theoretical bite force may be associated with numerous other selective pressures including maintenance of an apical position within the ecosystem.