6 - Swimming Mechanics and Energetics of Elasmobranch Fishes

Abstract

1. Introduction 2. Elasmobranch Locomotor Diversity 3. Elasmobranch Kinematics and Body Mechanics 4. Hydrodynamics of Elasmobranch Locomotion 5. The Remarkable Skin of Elasmobranchs and Its Locomotor Function 6. Energetics of Elasmobranch Locomotion 7. Climate Change: Effects on Elasmobranch Locomotor Function 8. Conclusions The remarkable locomotor capabilities of elasmobranch fishes are evident in the long migrations undertaken by many species, in their maneuverability, and in specialized structures such as the skin and shape of the pectoral and caudal fins that confer unique locomotor abilities. Elasmobranch locomotor diversity ranges from species that are primarily benthic to fast open-ocean swimmers, and kinematics and hydrodynamics are equally diverse. Many elongate-bodied shark species exhibit classical undulatory patterns of deformation, while skates and rays use their expanded wing-like locomotor structures in oscillatory and undulatory modes. Experimental hydrodynamic analysis of pectoral and caudal fin function in leopard sharks shows that pectoral fins, when held in the typical cruising position, do not generate lift forces, but are active in generating torques during unsteady swimming. The heterocercal (asymmetrical) tail shape generates torques that would rotate the body around the center of mass except for counteracting torques generated by the ventral body surface and head. The skin of sharks, with its hard surface denticles embedded in a flexible skin, alters flow dynamics over the surface and recent experimental data suggest that shark skin both reduces drag and enhances thrust on oscillating propulsive surfaces such as the tail. Analyses of elasmobranch locomotor energetics are limited in comparison to data from teleost fishes, and data from batoids are particularly scarce. We present an overview of comparative data on elasmobranch energetics, with comparisons to selected teleost fishes: generally, teleost fishes exhibit low costs of transport compared to elasmobranchs. Many elasmobranch species are particularly susceptible to changing oceanic conditions in response to climate change as a result of benthic habitat, reproductive mode, or reproductive site fidelity. Experimental studies on skates demonstrate that even small changes in water temperature can negatively impact locomotor performance, and locally adapted populations can differ in how they respond to abiotic stressors.