A comparative morphological analysis of body and fin shape for eight shark species
Published on 19. August 2017
A comparative morphological analysis of body and fin shape for eight shark species
Duncan J Irschick, Amy Fu, George Lauder, Cheryl Wilga, Chi-Yun Kuo, Neil Hammerschlag
ABSTRACT:
Sharks are diverse and ecologically important predators and are also highly varied in their biology and behaviour. Prior studies have posited basic relationships between body form and lifestyle; previous investigations of body shape in sharks, however, have been restricted to a few species, or measured dead sharks, which may show artefacts of preservation or distortion and/or require lethal sampling. Therefore, using non-lethal field methods, we examined body and fin shape in a group of eight different shark species that co-occur in coastal waters of the Western Atlantic but vary to different degrees in biology and ecology. We measured a series of 12 morphometric variables and body size (pre-caudal length) from wild individuals (N = 90 sharks total) belonging to the families Carcharhinidae [order: Carcharhiniformes (tiger, bull, blacktip, lemon, blacknose, Atlantic sharpnose and sandbar)] and Ginglymostomatidae [order: Orectolobiformes (nurse)]. By taking phylogeny into account using the SLOUCH method, our analysis revealed isometry of all 12 morphological variables measured relative to body length among all species, indicating that despite substantial lifestyle differences, the general body form of these carcharhiniform and orectolobiform species is overall highly conserved. Univariate analyses were consistent with this result in showing no substantial differences among species once the effects of body size were accounted for, although there was a modest difference among the species in leading edge of the caudal fin, which was also revealed by an elliptic Fourier analysis. A multivariate principal component analysis showed some differentiation among species in the height of the dorsal fin, the length of the lower lobe of the caudal fin and in overall body girth, but the lack of significant variation in the univariate analyses suggests that such differences may not be biologically substantial. Our conclusion was that these sharks are similar in gross morphology, which underscores the generality of the shark body form for different niches. Indeed, the most important variable distinguishing the species was variation in body length, which in sharks is generally linked to variation in diet type or breadth.
Biological Journal of the Linnean Society, blx088, DOI: 10.1093/biolinnean/blx088