Patterns of growth and the effects of scale on the feeding kinematics of the nurse shark (Ginglymostoma cirratum)

Abstract

Successful capture of prey often depends, in part, on the magnitude, duration and speed of feeding behaviours. Animal size and experience are potentially important to these aspects of behaviour, but the effects of scale on the muscular dynamics of and capture by aquatic vertebrates remain relatively unknown. This study examines scale effects on prey capture kinematics in the nurse shark Ginglymostoma cirratum, an inertial suction feeder. Morphometric analyses were performed on the heads and feeding apparati of 12 specimens between 71 and 244 cm total length (TL). These data indicated isometric growth of the feeding apparatus. The kinematics of prey capture in another 12 specimens (33 to 268 cm TL) were recorded with high speed video (200 fps). Across the size range, maximal angular excursions remained constant whereas the maxima of linear excursions increased isometrically. However, various phases of the prey capture sequence apparently did not increase in duration. Regressions of the components of prey capture timing generally had slopes between 0 and 0.5, supporting a model of muscular scaling initially proposed for largemouth bass. This model implies that increases in the duration of prey capture are the result of physiological constraints on muscular contraction. There is also a pattern of scaling across several taxa of aquatic vertebrates consistent with a second model of musculoskeletal scaling, although it does not necessarily apply within each taxon.