Locomotion in the Biology of Large Aquatic Vertebrates

As aquatic vertebrates increase in size, hydrofoils, which use lift to generate thrust, are increasingly used as propulsors. One factor affecting the magnitude of the lift force is the area of the propulsor. Resistance to cruising and sprints is mainly due to drag, but inertia is important during maneuvers when animals accelerate or turn. The inertia of the body and entrained water, which is proportional to body volume, resists acceleration. Because a thrust that is proportional to surface area is used to maneuver a resistance that is proportional to volume, acceleration performance and maneuverability are expected to decline with increasing size, This trend is ameliorated to some extent by the high swimming speeds attainable by warm-bodied vertebrates and the reduced resistance to acceleration characteristic of the skeletons of dolphins and ichthyosaurs. Maneuvers are essential for capture of elusive prey and avoidance of predators. As they increase in size, aquatic vertebrates use various means to ensure that their prey are less maneuverable than they. These include consumption of increasingly smaller prey relative to predator body size (culminating in filter feeding by the largest aquatic vertebrates); behaviors to concentrate, disturb, and disorient prey; and ambushing or suction feeding that avoid whole-body acceleration. Advantages of warm muscles are seen in the ability of endotherms to take more maneuverable prey than can ectotherms of the same size. Young stages of large aquatic vertebrates could be especially vulnerable to predators; viviparity or spawning in productive patches provides for rapid growth through vulnerable stages.