Abstract
Metabolic rate is intricately linked to the ecology of organisms and can provide a framework to study the behaviour, life history, population dynamics, and trophic impact of a species. Acquiring measures of metabolic rate, however, has proven difficult for large water-breathing animals such as sharks, greatly limiting our understanding of the energetic lives of these highly threatened and ecologically important fish. Here, we provide the first estimates of resting and active routine metabolic rate for the longest lived vertebrate, the Greenland shark (Somniosus microcephalus). Estimates were acquired through field respirometry conducted on relatively large-bodied sharks (33–126 kg), including the largest individual shark studied via respirometry. We show that despite recording very low whole-animal resting metabolic rates for this species, estimates are within the confidence intervals predicted by derived interspecies allometric and temperature scaling relationships, suggesting this species may not be unique among sharks in this respect. Additionally, our results do not support the theory of metabolic cold adaptation which assumes that polar species maintain elevated metabolic rates to cope with the challenges of life at extreme cold temperatures.
Highlights
Organisms inhabiting extreme environments have long been of special interest to ecologists, physiologists and evolutionary biologists a like[1,2], as these environments, including the poles, deserts and the deep sea are not rare, but cover vast expanses of the p lanet[3]
Drawing from a novel dataset comprised of oxygen consumption rates measured through field respirometry trials, we provide the first estimates of resting and active routine metabolic rate for the Greenland shark
Our whole-animal resting routine metabolic rate (rRMR) results for Greenland sharks indicate that these fish have very low energetic needs
Summary
Organisms inhabiting extreme environments have long been of special interest to ecologists, physiologists and evolutionary biologists a like[1,2], as these environments, including the poles, deserts and the deep sea are not rare, but cover vast expanses of the p lanet[3]. Unique data for extreme-temperature adapted species can broaden the scope and confidence of interspecific metabolic scaling relationships that aid in the development of ecologically relevant bioenergetic and evolutionary h ypotheses[10]. Despite the obvious uniqueness of Greenland sharks, their size and tendency to inhabit deep and remote areas of the ocean has made studying them expensive and logistically difficult[26] Even so, their relatively high trophic position (4.2–7.730) and abundance (up to 15.5 individuals per km2 31) imply that they are important top-down regulators in Arctic food webs. Through the scavenging of large carcasses (e.g. whale falls), Greenland sharks contribute to nutrient cycling which could aid in stabilizing food w ebs[32]
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