Superimposed on inherently high basal metabolic demands, the additional energetic requirements of reproduction can push female sea otters beyond physiological limits. Indeed, the resulting energy imbalance contributes to disproportionately high rates of mortality at the end of lactation in this species. To examine and quantify metabolic changes associated with reproduction, we measured the resting metabolic rate (RMR) of a female sea otter across gestation, lactation and non-reproductive periods. Concurrently, measurements were made on a non-breeding control female. Our results suggest that RMR declines during gestation. Conversely, RMR increases during lactation, reaches a peak at 3–4 months postpartum, and remains elevated until weaning. Combining these direct measurements with published data, we found the cost of pup rearing to be significantly higher than previously estimated. High baseline energy demands and limited energy reserves, combined with significant lactation and pup rearing costs, appear to necessitate metabolic and thermal lability during key reproductive stages.
The authors declare no competing or financial interests.
N.M.T. and T.M.W. conceived and designed the study. N.M.T., T.L.K. and B.P.R. conducted all experiments. N.M.T. analyzed the data. N.M.T. wrote the manuscript with editorial advice provided by all authors.
Funding was provided by the Otter Cove Foundation; the Monterey Bay Aquarium; the National Science Foundation [1210591 to J. A. Estes and N.M.T]; and the Office of Naval Research [N00014-080101273 to T.M.W.].
- Received February 17, 2016.
- Accepted May 16, 2016.
- © 2016. Published by The Company of Biologists Ltd