Only 139 Left: Research Shows Hawaii’s Rarest Whales Running Out Of Food

One Whale Lost 28% of Its Body Weight in 10 Weeks. It’s Not an Isolated Case

Off the coast of Maui, a small group of some of the rarest whales on Earth is quietly disappearing, and scientists now have a new window into just how dire things have gotten. Using drones, researchers measured the body condition of endangered false killer whales living around the main Hawaiian Islands, and what they found paints a troubling picture of animals caught in a squeeze between environmental stress, changing prey resources, and the daily demands of survival.

False killer whales, large dark-colored dolphins that despite their name look nothing like killer whales, are in serious trouble in Hawaii. Listed as endangered under the federal Endangered Species Act, the main Hawaiian Islands population has been shrinking at roughly 3.5% per year over the last decade, with only an estimated 139 individuals remaining as of 2022. Some of the fish they eat, including large game fish also targeted by fisheries, have shown long-term declines or smaller average sizes in Hawaiian waters.

Published in Endangered Species Research, the study produced the first detailed body condition assessments for this population, tracking 68 individual whales across 142 measurements taken between 2019 and 2025. Some animals are burning through their body reserves at alarming rates, and 2020 stood out as especially grim, coinciding with record ocean temperatures and the largest single-year population drop on record.

How Drones Are Helping Scientists Weigh Wild False Killer Whales

Flying camera-equipped drones over surfacing whales and measuring body width and length to estimate body volume, the team built a proxy for how fat or thin each animal was at any given moment. A plumper whale relative to its length is a healthy whale; a thin one is burning reserves it can’t afford to lose. Researchers flew at altitudes between 15 and 35 meters, capturing high-resolution video processed into detailed measurements.

To confirm reliability, they cross-checked drone estimates against three-dimensional body scans of false killer whales under human care at an aquarium in Okinawa, Japan. Animals were scanned with a handheld 3D scanner while trained to remain still, and the drone-based volume estimates came within about 3% of those scans.

Social Groups Tell Different Stories About False Killer Whale Health

Not all of the whales are struggling equally. These false killer whales are organized into at least four distinct long-term social clusters, each with its own general territory around the Hawaiian Islands. Body condition varied significantly depending on which cluster an animal belonged to.

Clusters 1 and 4 showed similar overall patterns, while Cluster 2 showed a different size-to-volume relationship that the authors say may be consistent with reduced body condition, though they caution that small sample size and limited body-size range in that cluster make the finding less certain.

Cluster 1 was where things got most dramatic. Three whales met the threshold for a biologically meaningful drop in body condition. One animal, identified as individual #0109, showed an estimated body mass loss of 234 kilograms, about 28% of its body mass, over just two and a half months. Another individual, #0086, remained in near-neutral or negative body condition across all sightings and showed visible signs of poor health, including a sunken blowhole, a recognized indicator of severe nutritional stress in dolphins and whales.

Cluster 1 also covers one of the largest geographic areas among the four groups, raising the possibility that some animals may face higher travel costs as they move through a wider range.

2020 Was a Terrible Year for False Killer Whales

That year produced the lowest average body condition scores across all social clusters, coinciding with a marine heatwave that pushed sea surface temperatures to record highs and the largest single-year population decline on record for this group. Marine heatwaves can disrupt food webs, and the timing is worrying, though the study cannot prove the heatwave caused the drop in body condition.

Data cited in the study show that the average weight of mahimahi caught in Hawaiian waters dropped 27% between the 2013 to 2017 average and 2022, while average wahoo weights fell about 9% over the same period. Smaller fish mean fewer calories per catch, and for an animal that may need to consume several percent of its body weight daily just to maintain condition, that math gets dangerous quickly. Calves are especially exposed: younger whales carry proportionally more body width than adults, a sign of greater energy reserves built up early in life, but those reserves depend entirely on whether their mothers can find enough to eat.

Why Tracking False Killer Whale Body Condition Matters

With only around 139 animals left, every individual counts. Drone-based monitoring requires no capturing or tagging, giving scientists a way to detect nutritional stress before it becomes fatal and to track how environmental changes affect population health in near-real time.

What the data already shows is that the pressures on these whales are real, measurable, and continuing. A whale that loses more than a quarter of its estimated body mass in two and a half months is more than a data point. It is a warning.

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Disclaimer: The findings of this study are based on observational data and drone-based measurements. Results should not be interpreted as definitive proof of causation between environmental factors and whale health outcomes. Conservation decisions should consider the full body of available research.

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