Nutritional stress and warming seas threaten Hawaiʻi’s last false killer whales
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Aerial view of two false killer whales near Hawaiian Islands
view moreCredit: Pacific Whale Foundation
A seven-year collaborative study has revealed alarming fluctuations in the health of Hawaiʻi’s endangered insular false killer whales, with some individuals losing nearly a quarter of their body weight in just a few months. Published today in Endangered Species Research, the findings provide the first quantitative evidence that nutritional stress and environmental shifts may be driving the decline of this iconic population, which now numbers fewer than 140 individuals.
The research—a partnership between the Pacific Whale Foundation (PWF), the Marine Mammal Research Program (MMRP) at UH Mānoa Hawaiʻi Institute of Marine Biology, and the Okinawa Churashima Foundation—utilized high-resolution drone photogrammetry to track 68 whales (roughly half the remaining population) between 2019 and 2025.
Rapid Declines and Climate Links
The study documented extreme physiological shifts, including one individual that lost an estimated 28% of its body mass—approximately 500 pounds—over a 10-week period. Researchers also found that the population’s overall Body Condition Index hit a record low in 2020. This decline coincided with a severe marine heatwave and the largest single-year population drop in recent history, suggesting that rising ocean temperatures are directly impacting the whales' ability to maintain necessary energy reserves.
“This study is a critical step in understanding whether prey limitation is driving the extinction risk for these whales,” explains Jens Currie, Chief Scientist at PWF, MMRP PhD candidate, and lead author of the study. “Our findings suggest that many individuals are living on a thin metabolic margin. We are now examining how competition with fisheries for high-energy prey like ‘ahi (yellowfin tuna) and mahimahi may be forcing these whales into a state of chronic nutritional stress.”
Mapping Health Across the Archipelago
The research highlights that health is not distributed equally across the population. Whales in "Cluster 1," known for traveling broad distances across the islands, showed significant variability in their physical condition. This suggests that the high energetic cost of moving long distances to find prey may be taking a heavier physical toll on certain social groups than others.
To ensure the highest level of accuracy, the research team validated their drone measurements against 3D scans of whales in human care at the Okinawa Churashima Foundation in Japan. This calibration provided the foundational data needed to convert aerial images into precise weight and volume estimates, confirming that the study’s measurements are accurate to within 3%.
“This level of precision allows us to pinpoint exactly when and where these whales are struggling, which is key for directing conservation efforts,” notes Lars Bejder, MMRP Director, HIMB Professor, and co-author of the study.
“This partnership shows how research facilities throughout the Pacific ocean can play a meaningful role in global conservation,” says Nozomi Kobayashi, Chief Research Scientist at the Okinawa Churashima Foundation Research Institute. “Using precise 3D scans from animals in our care to support the recovery of endangered populations in Hawaiʻi is both powerful and inspiring.”
A Cultural and Ecological Loss
The whales found in Hawaiʻi are a distinct, island-resident population adapted to the region’s coastal ecosystems and dependent on these waters for survival. They represent one of the smallest and most endangered whale populations in the United States, where the loss of even a few animals can have consequences for the entire population.
The loss of these apex predators resonates beyond biology. “Hawaiian culture has been losing many kūpuna, elders who carry the libraries of knowledge in cultural practices,” shares Kaʻapuni, Cultural Advisor at PWF. “Losing our native population of false killer whales removes even more knowledge from our islands and our history. We cannot afford to lose any more pieces of Hawaiʻi.”
Next Steps: A Foundation for Survival
Whales and dolphins today face multiple stressors, including climate change, entanglement in fishing gear, and pollution. Ensuring that false killer whales have enough food can help improve their resilience to these pressures. False killer whales in Hawaiʻi feed on large pelagic fish such as mahi-mahi, ono, aku, and ʻahi—species that are also favored by humans and targeted by fisheries. Understanding whether prey limitations are contributing to the population’s decline is a critical next step in their conservation.
“That is why this work is so important,” emphasizes Bejder. “These findings highlight the need to better understand the energetic requirements of these whales and how external stressors may be affecting them.”
As the population continues to decline at an average rate of 3.5% per year, this study represents a milestone: the first comprehensive effort to track the body mass and physical condition of individuals within Hawaiʻi’s endangered false killer whale population. Establishing this baseline is a critical turning point for management. Future studies built upon this foundational data will be the key to identifying shifting health trends in real-time, allowing for the robust management of pelagic fish stocks and the informed policy decisions necessary for the species’ long-term survival.
A false killer whale suspended above the water, after launching its prey high into the air
Credit
Pacific Whale Foundation
Journal
Endangered Species Research
Method of Research
Observational study
Subject of Research
Animals
Article Title
Body condition differs among social clusters and across years in endangered false killer whales in Hawai‘i
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