Asian small-clawed otters (Amblonyx cinerea): resting and swimming metabolic rates

Abstract

Open-flow oxygen and carbon dioxide respirometry was used in Neumünster Zoo (Germany) to examine the energy requirements of six Asian small-clawed otters (Amblonyx cinerea) at rest and swimming voluntarily under water. Our aim was to compare their energy requirements with those of other warm-blooded species to elucidate scale effects and to test whether the least aquatic of the three otter species differs markedly from these and its larger relatives. While at rest on land (16 °C, n = 26), otters (n = 6, mean body mass 3.1 ± 0.4 kg) had a respiratory quotient of 0.77 and a resting metabolic rate of 5.0 ± 0.8 Wkg⁻¹(SD). This increased to 9.1 ± 0.8 Wkg⁻¹ during rest in water (11–15 °C, n = 4) and to 17.6 ± 1.4 Wkg⁻¹ during foraging and feeding activities in a channel (12 °C, n = 5). While swimming under water (n = 620 measurements) in an 11-m long channel, otters preferred a speed range between 0.7 ms⁻¹ and 1.2 ms⁻¹. Transport costs were minimal at 1 ms⁻¹ and amounted to 1.47 ± 0.24 JN⁻¹ m⁻¹ (n = 213). Metabolic rates of small-clawed otters in air were similar to those of larger otter species, and about double those of terrestrial mammals of comparable size. In water, metabolic rates during rest and swimming were larger than those extrapolated from larger otter species and submerged swimming homeotherms. This is attributed to high thermoregulatory costs, and high body drag at low Reynolds numbers.