New publication: Energetic scaling of propulsive costs across body sizes in humpback whales
Updated: Aug 20
We are pleased to share a new publication in Marine Ecology Progress Series, entitled: Energetic scaling of propulsive costs across body sizes in humpback whales.
Authors: Cameron Nemeth, William Gough, Martin van Aswegen, Gussie Hollers, Lewis Evans, Andrew Szabo, and Lars Bejder
Abstract
Movement is energetically expensive, and locomotor efficiency depends on body size and morphology. Humpback whales Megaptera novaeangliae exhibit a remarkable ontogenetic size range and experience periods of intense fasting coinciding with energetically demanding migration, lactation, and growth. To quantify how propulsive costs scale with body size, we combined accelerometry data and aerial photogrammetry collected from 62 humpback whales ranging from calves to adults (4.4 to 14.1 m) on their Hawaiian breeding ground. Using a hydrodynamic model incorporating swimming kinematics and morphology, we found that mass-specific propulsive costs declined with increasing body length, representing a 62% reduction between a 4 m calf and a 14 m adult. Elevated activity levels and higher mass-specific propulsive costs in calves energetically burden lactating females, whose energy reserves must support both calf activity and rapid somatic growth. These energetic demands are buffered by the female’s own reduced activity and mass-specific propulsive costs. We estimate that propulsion accounts for approximately 21% of a lactating female’s daily energetic expenditure while on their breeding grounds. Our approach highlights the disproportionately higher cost of displacement in smaller individuals, ranging from approximately 4 kJ m⁻¹ in calves to 25 kJ m⁻¹ in adults, providing a scalable framework to quantify the energetic consequences of disturbance. These findings underscore the importance of large body size in baleen whales, refine understanding of how activity costs scale across body size in humpback whales on their breeding grounds, and provide an energetic baseline to predict consequences of environmental and anthropogenic disturbance.
Study overview
Over six consecutive years, from 2020-2025, our team deployed suction cup biologging tags as part of our broader goal to understand and quantify cetacean energetic budgets. The aim of this study was to examine the scaling of locomotor costs across body sizes in humpback whales, using a hydrodynamic model that MMRP post-doctoral researcher Will Gough developed for pilot whales in the Hawaiian islands. During these six field seasons, our team deployed 62 tags on individuals ranging from 4-14 m, and recorded over 90,000 tailbeats.
One of the clearest patterns to emerge from our study was how dramatically the energetic cost of swimming changes as humpback whales grow. By combining drone photogrammetry with high-resolution biologging tag data, we estimate that the mass-specific energetic cost of propulsion declines by ~62% between a 4 m calf and a 14 m adult. While larger whales were far more efficient swimmers, calves weren't simply paying a higher energetic cost because they were small—they were also much more active. Calves averaged approximately 403 tailbeats per hour, nearly three times the stroking rate of lactating females. Interestingly, this activity declined as calves aged throughout the breeding season, suggesting an ontogenetic shift in behavior. Young calves spend much of their time swimming, practicing, and developing the muscles and physiological capacity needed for migration. As they grow larger and more efficient, they gradually reduce their activity, presumably allowing more of their mother's limited energy reserves to be invested in continued growth before the long journey to northern feeding grounds. We estimated that propulsion accounts for approximately 21% of a lactating female's daily energy expenditure on the Hawaiian breeding grounds, highlighting how mothers conserve energy while simultaneously supporting the high activity levels and rapid growth of their calves.
Our results reinforce a broader pattern emerging across baleen whale research: being enormous provides substantial energetic advantages. As humpback whales grow, swimming becomes progressively cheaper on a body-mass basis, allowing larger whales to travel farther, migrate more efficiently, and allocate more energy toward reproduction and survival. These findings add to growing evidence that the evolution of gigantic body size in baleen whales is not simply a consequence of feeding ecology, but also provides profound energetic benefits throughout their lives.
Beyond understanding whale biology, these energetic estimates provide an entirely new way to quantify the cost of disturbance. Rather than simply recording that a whale moved away from a vessel or another stressor, we can now approximate how much energy that response required on a finer scale than ever before. Because our model calculates energetic costs per stroke and per meter traveled across different body sizes, future studies can estimate the energetic consequences of disturbances such as whale-watching vessels, sonar exposure, or repeated avoidance behavior. Importantly, these costs are not equal across all whales. Smaller individuals pay a disproportionately higher energetic price for movement, meaning the same behavioral response may have much greater biological consequences for calves than for adults. This energetic balance and transfer between mothers and calves in Hawaii is both crucial and delicate, especially given the extreme cost of lactation and the demands of growth in young humpback whales.
Acknowledgments
This research was made possible through support from the University of Hawaiʻi at Mānoa, the U.S. Department of Defense's Defense University Research Instrumentation Program, the Office of Naval Research, U.S. Navy's Living Marine Resources Program, the Pacific Whale Foundation, United States Pacific Fleet Environmental Readiness Division, ‘Our Oceans’, Netflix, Wildspace Productions and Freeborne Media, the National Marine Sanctuary Foundation, the Marine Mammal Commission, the Omidyar ʻOhana Foundation, Young Brothers, and the Dolphin Quest General Science and Conservation Fund. We are also deeply grateful for the generous philanthropic support of Dalia and JP Maheu and the Jaffe Foundation. We additionally thank Dr. Jeremy Goldbogen for his support of W.G. through NSF IOS-1656691, and Dr. Alec Burslem for his guidance on our statistical framework.
Permits
All research was conducted under National Oceanic and Atmospheric Administration (NOAA) research permits #21476 and #27548, with approval from the University of Hawaiʻi Institutional Animal Care and Use Committee (IACUC). Drone operations were performed by FAA Part 107-certified pilots in accordance with all Federal Aviation Administration regulations, and no behavioral responses to drone operations were observed during the study.
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Full citation: Nemeth C, Gough WT, van Aswegen M, Hollers A, Evans L, Szabo A, Bejder L (2026) Energetic scaling of propulsive costs across body sizes in humpback whales. Mar Ecol Prog Ser 792:meps15212 https://doi.org/10.3354/meps15212
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The finding that calves stroke nearly three times as often as lactating females, yet the female's own reduced activity buffers the calf's high mass-specific costs, raises an interesting question about the mother's energy budget. If propulsion is only about 21% of her daily expenditure, what accounts for the rest during fasting on the breeding grounds, and could small shifts in her activity level meaningfully extend how long she can sustain lactation before returning to feeding grounds?
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