Swimming Metabolism of Yearling and Adult Harbor Seals Phoca vitulina

The swimming metabolism of yearling and adult harbor seals was measured by indirect calorimetry in a flow channel at speeds ranging from 0.5 to 1.4 m·s−1. Minimum resting metabolic rates in still water were 5.1 and 4.6 ml O2·min−1·kg−1 for the two yearling seals (body mass [Mb] = 33 kg) and one adult seal (Mb = 63 kg), respectively. Minimum resting metabolic rates were about 1.1 × the predicted standard metabolic rate for mammals of equivalent size. During steady-state swimming, metabolism increased curvilinearly with speed and was best described by the equation V̇o2 (ml O2·min−1·kg−1) = 5.1 + 6.25 velocity (m·s−1)1.42 for the yearling seals and V̇o2 = 4.6 + 3.1 velocity1.42 for the adult seal. Stroke frequency increased linearly as a function of swimming speed. Cost of transport decreased asymptotically with swim velocity, approaching a minimum at 1.0–1.4 m·s−1 of 3.6 J·m−1·kg−1 for yearling and 2.3 J·m−1·kg−1 for adult seals. The minimum cost of transport was less than for other semiaquatic birds and mammals but 3–4 × the predicted value for salmonid fish of equivalent size at 25 C.