Bioenergetics of marine mammals: the influence of body size, reproductive status, locomotion and phylogeny on metabolism

• Main Author: Maresh, Jennifer L.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: eScholarship, University of California 2014
• Subjects: Ecology; Physiology; Animal behavior; allometry; basal metabolic rate; disturbance; field metabolic rate; Elephant Seals
• Online Access: http://www.escholarship.org/uc/item/3c5785r3; http://n2t.net/ark:/13030/m5bs06bc

Metabolic energy demand is both a cause and consequence of how animals interact with their environments. Describing patterns of metabolism and understanding the drivers underscoring those patterns have been long-standing goals of biology for almost a century. Mammals are often the subject of comparative metabolism studies, and it is clear that their metabolic rates are determined by a complex interaction between a host of morphological, ecological, behavioral and evolutionary factors. In contrast, metabolism is often considered to be less complex for marine mammals, that is, uniformly high across all groups. This perception is the result of a paradigm that took root when determinations on marine mammals were relatively rare, and it has persisted despite a growing number of studies reporting low to moderate metabolic rates in some species. In the following chapters, I describe the foraging energetics of free-swimming northern elephant seals ( Mirounga angustirostris ) and show that these seals have extremely low field metabolic rates (FMRs) that do not conform to traditional expectations for marine mammals. I also demonstrate the effects of body size and reproductive status on the bioenergetics of this species, showing that larger, fatter, pregnant seals have lower FMRs and higher foraging success. I also am able to demonstrate the importance of locomotory efficiency in maintaining a low FMR: seals responded to artificially increased locomotion costs by increasing their swimming efforts, thereby increasing FMR and lowering foraging success. These results demonstrate the sensitivity of elephant seals to anthropogenic disturbance in important foraging grounds, and potentially along migration corridors.These results also demonstrate an energy economy strategy in a species that, by virtue of its shared environment with other marine mammals, would traditionally be predicted to have an elevated metabolic rate. In my last data chapter, I revisit the paradigm underscoring these traditional predictions. I synthesize all mammalian metabolic determinations published to–date and am able to show that the metabolic rates of marine mammals are comparable to those of terrestrial mammals, particularly when they are compared to other carnivores. I also discuss the importance of differences between the various marine mammal groups in their ecologies, behaviors and evolutionary histories in determining metabolic energy demand. These results suggest that metabolism in marine mammals is as complex as in other mammals, and that the assumption of one uniform, high–energy group is not supported by the data. This has important implications for managers interested in predicting the prey requirements of these upper trophic level predators, as traditional models are likely to exaggerate the impact of many species on their environments.