A new study led by University of Hawai'i (UH) at Mānoa researchers reveals how extreme ocean warming disrupts whale metabolism, nutrition, and reproductive success and what the developing 2026-2027 El Niño could mean next. As climate change drives increasingly intense marine heatwaves, scientists are uncovering how these extreme warming events disrupt the biology of humpback whales.
Earlier reports from NOAA, academic researchers, and regional monitoring programs documented troubling symptoms during the 2014–2016 Pacific marine heatwave, known as the Blob: fewer humpback whale sightings in Hawai'i and Alaska, declines in calf numbers, and widespread signs of nutritional stress. Until now, the physiological mechanisms behind these population‑level changes remained unclear. The study, published in iScience, provides the missing link.
"These findings give us a window into how whales actually cope with extreme environmental stress," said lead author Ching-Tsun Chang, a former graduate student in the Department of Oceanography at the UH Mānoa School of Ocean and Earth Science and Technology and now an assistant professor at National Sun Yat-sen University, Taiwan. "We've known from previous reports that humpback whales declined in number and body condition during the Blob. What we show here is the physiological story behind those patterns: how whales adjust their metabolism, how nutrient use shifts, and how reproduction may be compromised."
How whales coped internally
To understand how whales responded physiologically, researchers analyzed nearly eight years of biochemical records preserved in the baleen of stranded female humpbacks from Hawai'i. Baleen grows continuously, creating a natural timeline of metabolic signals.
"Baleen is an extraordinary archive," said co‑author Kristi West, Director of the UH Health and Stranding Lab and associate researcher in Human Nutrition, Food and Animal Sciences at the UH Mānoa College of Tropical Agriculture and Human Resilience . "It lets us reconstruct an animal's nutritional and reproductive history with fine detail. By pairing these biochemical records with bioenergetic models, we can finally see how climate extremes ripple through a whale's body."
Using compound‑specific isotope analysis of amino acids paired with bioenergetic models, which are computer models that estimate how animals use and allocate energy, the team reconstructed how whales routed nutrients and mobilized energy reserves before, during, and after the heatwave.
The results reveal the physiological mechanisms behind previously observed declines. During the heatwave, whales essentially "powered down", slowing their metabolism to stretch limited food supplies. This lack of nutrition made early pregnancy harder to maintain, even if whales became pregnant. Additionally, one whale's decades-long history shows the cumulative toll of environmental change, with its baleen preserving a five‑year record of how shifting ocean conditions affected its body late in life.
Vulnerability to 2026–2027 El Niño and climate
Capital breeders are animals that rely on energy stored during feeding seasons to fuel migration, pregnancy, and lactation. When feeding seasons are disrupted—as during marine heatwaves—these species have limited ability to compensate.
The new findings arrive as the Pacific enters a developing 2026–2027 El Niño, which is expected to be one of the strongest on record bringing unusually warm conditions across the North Pacific. Seasonal forecasts from international climate centers project widespread surface ocean warming that could reduce prey availability in key humpback whale foraging regions. While this event is distinct from the 2014–2016 Blob, the anticipated warming highlights why understanding whale physiological responses to extreme environmental stress is increasingly important.
"As marine heatwaves become more frequent, capital‑breeding species like humpback whales may face increasing challenges in a rapidly warming ocean," said Brian Popp, co-author and professor of Earth Sciences in the UH Mānoa SOEST. "Understanding these physiological responses is essential for anticipating how populations will fare in the decades ahead."
