Are morphological traits explaining swimming performances of several deep-sea sharks from New Zealand?

Sharks have been present in oceans for more than 400 millions of years and have survived several mass extinctions (Devonian, Permian, Triassic and Cretaceous). Although some morphological features are well preserved between all shark species (cartilaginous skeleton, lack of swim bladder, renewable teeth,...), they show remarkable adaptations to their different lifestyles. Among sharks, data regarding deep-sea species are scares, and especially about their ecology. In this work we focused on deep-sea sharks’ swimming performances. Indeed, as active predators, shark swimming capabilities take part in several essential behaviours such as hunting, escaping, home range, migratory behaviours. While the swimming performances are well studied on shallow-water sharks, only limited data about their deep-sea counterparts are available; at most it is suggested they are slow and lazy swimmers. However, recent study shows significant differences of swimming cruise speed between eight deep-sea sharks from New Zealand. Several studies about the shallow-water species show a high importance of morphological traits related with the swimming performances. Here we investigate what are the morphological traits that could take part in deep-sea sharks swimming cruise speed previously observed. We also measure the traits differences between species and correlate it with their phylogeny. Thirty morphological traits from eight deep-sea species and one surface species (control) were measured. These morphological traits include classical measurements of length from the fins or the body but also geomorphological features and ratios for the rostrum and different fins. First results of the statistical analysis seem to show out that variables like area of the pectoral or caudal fins (which play a major role for locomotion of surface sharks), are not the main factors influencing speed of deep-sea sharks. Conversely, rostrum length, distance between the first and the second dorsal fin with the caudal fin, seem to be factors separating the different speed groups.