Hawai'i's last false killer whales threatened by nutritional stress and warming seas

Hawai'i's last false killer whales threatened by nutritional stress and warming seas Sadie Harley Scientific Editor Robert Egan Associate Editor A seven-year collaborative study has revealed alarming fluctuations in the health of Hawaii's endangered insular false killer whales, with some individuals losing nearly a quarter of their body weight in just a few months. Published 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, the Marine Mammal Research Program at UH Mānoa Hawai'i Institute of Marine Biology, and the Okinawa Churashima Foundation—used 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—about 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 heat wave and the largest single-year population drop in recent history, suggesting that rising ocean temperatures are directly affecting 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," explained Jens Currie, chief scientist at Pacific Whale Foundation, a doctoral candidate in the Marine Biology Graduate Program, 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 long 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 on others. To ensure the highest level of accuracy, the research team validated its 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," said 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," said 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 Hawai'i is both powerful and inspiring." A cultural and ecological loss The whales found in Hawai'i 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," said Ka'apuni, cultural adviser at Pacific Whale Foundation. "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 Hawai'i." 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 Hawai'i feed on large pelagic fish such as mahi-mahi, ono, aku and 'ahi—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," Bejder said. "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 Hawai'i's endangered false killer whale population. Establishing this baseline is a critical turning point for management. Future studies built on this foundational data will be key to identifying shifting health trends in real time, allowing for robust management of pelagic fish stocks and informed policy decisions necessary for the species' long-term survival. Publication details Jens J Currie et al, Body condition differs among social clusters and across years in endangered false killer whales in Hawai'i, Endangered Species Research (2026). DOI: 10.3354/esr01505 Journal information: Endangered Species Research Key concepts endangered speciesmarine biologycommercial fishery resourcesendemic speciesfishery managementdolphinsProvided by University of Hawaii at Manoa