Energy metabolism of underwater swimming in river-otters (Lutra lutra L.).

We used a still-water swim channel in conjunction with open-flow oxygen and carbon dioxide respirometry to examine the energy requirements of river-otters (Lutra lutra L.) swimming voluntarily underwater in Neumünster Zoo (Germany). While at rest on land (5 degrees C), river-otters had a respiratory quotient of 0.77 and a resting metabolic rate of 4.1 W kg-1. This increased to an estimated 6.4 W kg-1 during rest in water (11-15 degrees C) and to 12.3 W kg-1 when the animals were feeding in the channel. River-otters swimming under water preferred a mean speed of 0.89 m s-1, and their energy requirements attained 11.6 W kg-1. Cost of transport, however, was minimal at 1.3 m s-1 and amounted to 0.95 J N-1 m-1.