Sea Otter Behavior: Morphologic, Physiologic, and Sensory Adaptations

Abstract

AbstractMorphology and physiology enable but also constrain an animal’s behavior and physical performance, and sensory systems affect how an animal perceives its environment. Sea otters are grouped with other raptorial predators even though they capture and manipulate prey with their forepaws and consume it at the water’s surface. They have a short, robust skull and mandibles that enhance bite force. Their postcanine teeth have rounded or conical cusps and large surfaces for cracking or crushing mollusk shells, crustacean exoskeletons, or the test of echinoderms, such as sea urchins. The axial skeleton of sea otters is modified for aquatic locomotion, with a flexible spine and foreshortened limbs to reduce hydrodynamic drag. Forelimbs are used to capture and manipulate prey and for using tools (e.g., rocks) to open hard-shelled prey, but not for locomotion. Sea otters use dorsoventral undulation with simultaneous pelvic paddling during routine submerged swimming, and their hindfeet are modified into flippers for more efficient thrust. Because of their large lung volume, sea otters are positively buoyant and rest (sleep) effortlessly or swim in supine position at the surface, using alternate stroking of the hind flippers, although they are clumsy and slow when walking on land. To offset the high thermal conductivity of water, sea otters have a mass-specific basal metabolic rate that is 2.9-fold higher than a terrestrial eutherian mammal. As a result, they consume about 25% of their body mass daily, which requires them to spend 14–50% of their activity budget foraging. Because sea otters rely almost exclusively on fur for thermal insulation, they groom (felt) their dense fur to trap an air layer next to the skin, and this essential behavior represents a significant part of the daily activity budget. Sea otters have dichromatic color vision, underwater acuity similar to other marine mammals, and the aerial acuity of many terrestrial mammals. Although sea otters detect underwater sounds, hearing is primarily adapted for air, and they do not vocalize underwater. Their forepaws have good tactile surface discrimination for identifying prey by touch, but the role of their vibrissae in foraging is uncertain. Sea otters discriminate odorants and have a vomeronasal gland, which may detect pheromones that convey social or sexual (endocrine) cues that influence behavior and reproductive physiology. Based on the presence of taste buds, sea otters may have a gustatory sense. Compared to cetaceans, the sensory systems of sea otters are more similar to amphibious pinnipeds and terrestrial carnivorans.KeywordsAuditionBehaviorCraniodentalDurophagyEfficiencyFurGustationInsulationMorphologyOlfactionPerformancePhysiologyRespirationSea otterSensorySleepTactileVisionVomeronasal gland