Abstract: The energy and food requirements of free-ranging pinniped species are difficult to measure and, as a consequence, are unknown for most species. They can be inferred from measures of Field Metabolic Rate (FMR) made by the Doubly Labeled Water (DLW) method, however. In this work, we confirmed our hypothesis that the FMR of pinnipeds measured by DLW can be described by an allometric relationship as a function of body weight. Although costly and difficult to apply, the DLW method is one of the few possible methods generating estimates of energy demands for unrestrained, free-living animals. The results of its application on two adult, male, free-living Atlantic Walruses (Odobenus rosmarus rosmarus), weighing 1,370 kg and 1,250 kg, respectively, estimated from length and girth measures, are presented here. These data extend the size range of the seven pinniped species for which the DLW method has been applied by a factor of 10. The animals were measured at a site in northeast Greenland (76° N) during the summer. FMR was dependent on the pool model for estimating metabolic rate and was approximately 13% higher when using the single-pool compared with the two-pool model. The estimates using the two-pool model were 328.1 (SE 8.7) MJ•day -1 and 365.4 (SE 15.4) MJ•day -1 for each of the two walruses. These figures were combined with estimated FMR using the same method in seven other pinniped species to derive a new, refined predictive equation for pinniped FMR (Ln-FMR [MJ•day −1] = 0.173 + 0.816 Ln-Total Body Mass [kg]). This equation suggests that pinniped food requirements might sometimes be twice as high as that assumed in some fisheries models, which are based on multiples of the theoretical basal metabolism.
Key Words: WALRUS; ODOBENUS ROSMARUS; FIELD METABOLIC RATE; FEEDING RATES; PINNIPEDS; DOUBLY LABELED WATER; GREENLAND
Document Type: Research article
Page Numbers: 363 - 369