Some of Hawaiʻi's endangered false killer whales are rapidly losing weight, a warning sign that warming oceans and limited prey may be pushing one of the nation's smallest whale populations closer to extinction, according to research published in Endangered Species Research by a team including scientists from the University of Hawaiʻi at Mānoa.
The findings provide the first quantitative evidence that nutritional stress and competition with fisheries may be accelerating the decline of this iconic population, which now numbers fewer than 140 individuals.
The research—a partnership between the Pacific Whale Foundation (PWF), Marine Mammal Research Program (MMRP) at UH Mānoa Hawaiʻi Institute of Marine Biology and 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 could be 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, PhD 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 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," said Lars Bejder, MMRP director, title="Hawaiʻi Institute of Marine Biology">HIMB professor, and co-author of the study.
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.
