Humpback calves require 38 times more energy after birth

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The energy required for newborn humpback calves to grow after birth is 38 times greater than what they needed inside the womb according to research from University of Hawaiʻi at Mānoa Hawaiʻi Institute of Marine Biology (HIMB) in collaboration with Alaska Whale Foundation and other key partners. These findings were published in Marine Ecology Progress Series.

"This study addresses a key piece of the energetic puzzle in estimating the cost of being a humpback whale in the North Pacific: the cost of growth," said Martin Van Aswegen, lead author of the study and postdoctoral researcher at HIMB's Marine Mammal Research Program (MMRP). "While previous research has shown that these whales must grow very large in a short period of time, the actual energetic expense of that accelerated growth remained unknown."

Geared to grow

Research revealed that calves require 6-8 times the daily growth energy of an adult whale, and they achieve 30% of their total lifetime growth in less than their first year of life. In fact, more than 60% of a calf's crucial energy needs for growth occur within the first 150 days of birth.

Humpback mothers must support lactation while fasting in Hawaiʻi breeding grounds and then traversing back to their feeding grounds in Alaska. This exposes the mother-calf pair to significant vulnerability when ocean conditions threaten the mother's energy stores.

The study found that a mother's ability to produce a large, healthy calf-one more resilient to starvation and environmental stress-hinges directly on her own energy reserves. Smaller females, with lower energy reserves, face trade-offs that constrain how often they can reproduce and how much they can invest in their offspring.

"By quantifying the energetic demands of growing big and strong, we provide crucial insight into how external pressures, including climate change and human disturbance, may affect the survival and resilience of these ocean giants," said van Aswegen.

Warning signs

The study also revealed a worrying trend: mature humpback whales today are noticeably shorter than historical records, indicating a decline in body size of approximately 1-2 feet since the mid-1900s. Recent signs of humpback population stress in the region include a 76.5% drop in mother-calf sightings and an estimated 80% drop in crude birth rates in Hawaiʻi between 2013-2018. These declines coincided with the longest-lasting global marine heatwave, suggesting that low food availability prevented mothers from getting enough energy for the demands of nursing and calf growth. The results affected calves and juveniles, whose higher energy requirements make them highly vulnerable.

"If humpback whales are to survive threats like extreme marine heatwaves and other stressors that result from human activity, we need to understand precisely how reproductive females accumulate and allocate energy to support the exponential costs of gestation and lactation," said Lars Bejder, director of MMRP, professor at HIMB, and senior author of the study. "This knowledge is the foundation for making the urgent conservation changes required for the population's future."

Drones, data

The team used drones to take high-resolution aerial photos of more than 1,500 humpback whales in Hawaiʻi and Southeast Alaska. They combined drone measurements with historical records and biological samples to acquire a full picture of humpback energetic needs throughout their lifespan.

"This non-invasive approach gives us a rare look at whale biology as they live, instead of relying only on historical whaling data from the 1900s," said van Aswegen. "Our humpback whale health database, comprising over 12,000 measurements of 8,500 individual whales in the North Pacific, is being used across several projects within the Marine Mammal Research Program and abroad."

The data can be used in conjunction with fine-scale behavior and movement data (from biologging tags), reproductive and stress hormone data (from tissue and breath samples), and tissue data derived from post-mortem events.

Partnerships

This work was made possible through MMRP, HIMB, Alaska Whale Foundation, Pacific Whale Foundation, University of Alaska Southeast, Glacier Bay National Park and Preserve, University of Alaska Fairbanks, Oregon State University, The Dolphin Institute (UH Hilo), UH Health and Stranding Lab, and HappyWhale. Hawai'i fieldwork was funded through UH Mānoa, the US Department of Defense's Defense University Research Instrumentation Program, the Office of Naval Research, 'Our Oceans,' Netflix, Wildspace Productions and Freeborne Media, the 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 Funds, and the North Pacific Research Board.

Photos:

Photo 1: A mother humpback whale with her calf on their Hawaiian breeding grounds. (Photo credit: Martin van Aswegen under NMFS Permit No: 21476)

Photo 2: The Alaska Whale Foundation field team on their inflatable research vessel, with pilot Martin van Aswegen landing the research drone. (Photo credit: Alexa Elliot)

Photo 3: Humpback whales surfacing on their Southeast Alaskan feeding grounds with the drone overhead measuring their body size. (Photo credit: Fabien Vivier under NMFS permit 19703)