New publication: Age-specific body length, mass, and energetic cost of growth in humpback whales

Written by Martin van Aswegen

We are pleased to share a new publication in Marine Ecology Progress Series, entitled: Age-specific body length, mass, and energetic cost of growth in humpback whales.

Authors: Martin van Aswegen, Andy Szabo, Jens Currie, Stephanie Stack, Jan Straley, Janet Neilson, Christine Gabriele, Kelly Cates, C. Scott Baker, Debbie Steel, Adam Pack, Kristi West, Nicholas Hofmann, Rob Toonen, Coral Loockerman, Florence Sullivan, Ted Cheeseman, Fred Sharpe and Lars Bejder.

Open access paper: https://doi.org/10.3354/meps14937.

Figure 1. Key data and modeling parameters. Data sources include life history data from (A) sighting histories, (B–D) morphometric estimates from unoccupied aerial system (UAS) photogrammetry, and (E) tissue samples and published literature, used to estimate body mass and energetic cost of growth in humpback whales (F). BC: body condition.

Measuring giants from the sky:

How do you measure and weigh a whale without ever touching it? We used unoccupied aerial systems (UAS; drones) to capture high-resolution images of 1,503 individual humpback whales on their Hawaiian breeding and Southeast Alaskan feeding grounds. By integrating these aerial measurements with individual sighting histories, historical whaling records and postmortem tissue samples (Figure 1), we estimated sex-specific body size, growth trajectories, and associated energetic demands from birth to 50 years of age. This non-invasive approach provides a rare perspective into whale biology as they live (Figure 2), rather than relying solely on historical whaling data from the 1900s.

The energetic cost of growing up

This study reveals the extreme energetic demands of early growth in humpback whales. Calves reach about 75 % of their adult length within the first year, but this rapid growth comes at a great cost: they allocate 6-8 times more energy to growth per day than mature adults. For mothers, this means sustaining nearly a third of their calf’s lifetime growth in just one year - while fasting on the breeding grounds and throughout migration, relying solely on fat reserves accumulated during the previous feeding season.

Why it matters in a changing ocean

Our findings demonstrate that the first year of life represents an exceptionally demanding energetic phase for humpback whales. The ability of females to meet these demands is directly linked to their size and condition, with larger whales possessing greater energy stores and thus greater reproductive resilience. However, recent marine heatwaves in the North Pacific have shifted the composition, quality, and availability of prey, leading to declines in humpback whale reproductive output, increased calf mortality, and fewer juveniles in the population. By quantifying the energetic thresholds associated with growth, this study highlights the vulnerability of mother-calf pairs to fluctuations in prey dynamics and underscores the importance of energy accumulation on feeding grounds for population resilience under ongoing climate change.

Figure 2. A pair of humpback whales surfacing on their Southeast Alaskan feeding grounds, measured by a drone overhead. Photo credit: Dr. Fabien Vivier, NMFS Permit: 19703.

In our commitment to making our science readily accessible to the Native Hawaiian community, this open-access paper includes an abstract in Hawaiian. By sharing this work in ‘Ōlelo Hawai‘i, we hope to strengthen the connection between our research and the community it serves, reflecting our commitment to both the conservation of these species and the protection of the land and waters they inhabit. We welcome discussion and further engagement from all who wish to connect. We thank Cameron Nemeth and Kalikoaloha Martin for translating the abstract into Hawaiian.

Acknowledgements:

We thank the numerous research assistants who helped with fieldwork and data processing. We also thank PacWhale Eco-Adventures, Chrissy Lovitt and Emma Nelson (Maui Ocean Adventures), Lee James, Jason Jones, and the Guth family for their support. We thank Charles Jurasz, Susan Jurasz, Peter Jurasz, and Ginny Palmer (Sea Search) for providing valuable long-term sighting data. We are also grateful to Marc Lammers (Oceanwide Science Institute) for providing sighting date information. We thank Elmer Ka‘ai for his support relating to humpback whale strandings and sample collection. We thank the following public Happywhale data contributors: Dennis Rogers, Jim Nahmens, and Andy Wolcott (Alaska Sea Adventures), Atlantis Cruises, Kenneth O’Brien (Fantasy Cruises), Jona­thon Whitney, Capt. Steves Rafting Adventures, Bruce Whit­tington (Bluewater Adventures), Paul Pudwell (Sooke Whale Watching), Kenneth Held (Safari Boat Excursions Maui, Maui Adventure Cruises), Brooke McKinley (Hawai‘i Ocean Sports), Eric Austin Yee (PacWhale Eco-Adventures), Tracy Desiderio (Harv and Marv’s Outback Alaska), John Forde (The Whale Centre Tofino), Dive Maui, Mindy Huston, Heather Baskey, Emily Cramer, and K. C. Dermody (Jay­leen’s Alaska). We are grateful to Zoltan Nemeth (cetek-art.com) for providing illustrations. 

Permitting:

Field research was conducted under National Marine Fisheries Service (NMFS) permit numbers 21476, 21321, and 19703, with all activities approved by the Univer­sity of Hawaii Institutional Animal Care and Use Commit­tee. Stranding response, necropsy, and sample collection of the humpback calves were conducted under NMFS permit numbers 18786 and 24359.

Funding:

Hawai‘i fieldwork was funded through the University of Hawai‘i at Manoa, the US Department of Defense’s Defense University Research Instrumentation Pro­gram, ‘Our Oceans’, Netflix, Wildspace Productions and Freeborne Media, Omidyar Ohana Foundation, the National Marine Sanctuary Foundation, and PacWhale Eco-Adventures, as well as members and donors of Pacific Whale Foundation. Southeast Alaska research was funded through awards from the National Geographic Society, the Lindblad Expeditions-National Geographic (LEX-NG) Funds, and the North Pacific Research Board. Graduate assistantships for M.v.A. were funded by a Denise B. Evans Oceanography Fellowship, North Pacific Research Board grant, and the Dolphin Quest General Science and Conservation Fund. Long-term humpback whale population monitoring in Glacier Bay and Icy Strait was funded by the National Park Service. Stranding response, necropsy, and tissue processing of the humpback whale calves were supported by the NOAA John H. Prescott Marine Mammal Rescue Assistance Grant Program.