NEW SHARK SCIENCE!

Published last week in the leading journal ECOLOGY, work led by PEAC Lab alumni Dr Evan Byrnes reveals the relationship between how much energy an animal needs and home range size is much more complex than we originally thought.

This demonstrates the value of contemporary tagging technologies for better understanding spatial ecology and highlights the importance of empirically testing existing theory.

Free-ranging lemon sharks (Negaprion brevirostris) in Bimini, Bahamas. Photograph and (C) Sophie Hart

For the first time, the relationship between metabolic rate and home range size has been tested in free-ranging animals. This work was part of Evan's PhD; in 2019, 20 lemon sharks (Negaprion brevirostris) ranging from 2.32 - 17.76 kg total body mass were tagged with acoustic tags inside an acoustic array at Bimini, Bahamas.

Lead author Dr Evan Byrnes surgically tagging a lemon shark with an acoustic tag that transmits location and acceleration data, with assistance from Bimini Biological Field Station staff. All shark captures and tagging procedures were performed in accordance with permits from the Bahamas Department of Marine Resources (MA&MR/FIS/178) and Murdoch University Animal Ethics committee (RW3119/19). Photo (C) Michael Scholl

For each individual shark, home range size and metabolic rate were estimated from the tags' location data and acceleration data input into a bioenergetic equation, respectively. As expected, both home range size and the metabolic rate of lemon sharks increased with body size at similar rates.

Home ranges of lemon sharks increased with body size. Kernel Utilisation Distributions (KUDs) for (A) the smallest shark (2.32 kg and 1.82 km2), (B) a mid-sized shark (9.74 kg and 9.38 km2), and (C) the largest shark (17.76 kg and 16.71 km2). Grey dots represent acoustic receiver locations. Figure 1 from Byrnes et. al., 2025. “ Intraspecific Scaling of Home Range Size and Its Bioenergetic Association.” Ecology 106(2): e70003. https://doi.org/10.1002/ecy.70003 Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.

While the relationship between home range size and metabolic rate was consistent with established theory, a surprisingly complex relationship was found when metabolic rate was considered in more details as both inactive and active components. The relationship between home range size and inactive metabolic rate was weaker than the relationship between home range size and active metabolic rate, irrespective of body size.

• Inactive metabolic rate = the minimum energy required to function at a basic level.

• Active metabolic rate = additional energy required for physical activity/exercise.

So what does this mean? The article discusses various reasons for this complexity, including smaller home range sizes attributed to high minimum energy requirements, high competition and/or limited resource availability, predator avoidance, physiology, and individual personality traits. The article also answers an important question about causation - what came first, the chicken or the egg? No, hang on...sharks...metabolic rate...home range size...Does a higher metabolic rate, which requires obtaining enough food, drive home range size? OR do increased travel costs linked to larger home ranges drive metabolic rate?

You'll have to read the open access paper to find out!

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This work was a collaboration between:

• Evan Byrnes, Adrian Gleiss, Jenna Hounslow & Stephen Beatty (Centre for Sustainable Aquatic Ecosystems, Harry Butler Institute & Environmental and Conservation Sciences, Murdoch University)

• Vital Helm (Department of Environmental Sciences, Zoology, University of Basel)

• Clemency White (Faculty of Health and Life Sciences, University of Exeter)

• Matthew Smukall (Bimini Biological Field Station Foundation)

Co-authors thank Bimini Biological Field Station staff, S. Hart, C. Mason, A. Warrior, J. Whicheloe, and K. Yang, as well as interns who assisted with capturing and tagging of sharks. We thank the late Dr. S. Gruber for his dedication to furthering the understanding of elasmobranch ecology and in generating a large body of foundational work on lemon shark physiology and ecology. In addition, we thank two anonymous reviewers and the handling and associate editors for their constructive feedback that we feel greatly improved this manuscript. This work was funded by Save Our Seas Foundation grants 260 and 402. Open access publishing facilitated by Murdoch University, as part of the Wiley - Murdoch University agreement via the Council of Australian University Librarians.