A killer appetite: metabolic consequences of carnivory in marine mammals

Among terrestrial mammals, the morphology of the gastrointestinal tract ref lects the metabolic demands of the animal and individual requirements for p rocessing, distributing, and absorbing nutrients. To determine if gastroint estinal tract morphology is similarly correlated with metabolic requirement s in marine mammals, we examined the relationship between basal metabolic r ate (BMR) and small intestinal length in pinnipeds and cetaceans. Oxygen co nsumption was measured for resting bottlenose dolphins and Weddell seals, a nd the results combined with data for four additional species of carnivorou s marine mammal. Data for small intestinal length were obtained from previo usly published reports. Similar analyses were conducted for five species of carnivorous terrestrial mammal, for which BMR and intestinal length were k nown. The results indicate that the BMRs of Weddell seals and dolphins rest ing on the water surface are 1.6 and 2.3 times the predicted levels for sim ilarly sized domestic terrestrial mammals, respectively. Small intestinal l engths for carnivorous marine mammals depend on body size and are comparati vely longer than those of terrestrial carnivores. The relationship between basal metabolic rate (kcal day(-1)) and small intestinal length (m) for bot h marine and terrestrial carnivores was: BMR = 142.5 intestinal length(120) (r(2) = 0.83). We suggest that elevated metabolic rates among marine mamma l carnivores are associated with comparatively large alimentary tracts that are presumably required for supporting the energetic demands of an aquatic lifestyle and for feeding on vertebrate and invertebrate prey. (C) 2001 El sevier Science Inc. All rights reserved.