VNR: UH calculates survival needs of deep-diving Hawaiian pilot whales

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For the first time, scientists have calculated a detailed "energetic budget" for Hawaiʻi's short-finned pilot whales, revealing what it takes to power their extreme, 800-meter (2,600-feet) dives for food. A new study led by the University of Hawaiʻi's Hawaiʻi Institute of Marine Biology (HIMB) found an average adult whale must eat 142 squid daily to survive, scaling up to 416 million squid annually for the entire population of short-finned pilot whales. This data, published in the Journal of Experimental Biology, provides a new benchmark for protecting the historically understudied marine mammals.

"Pilot whales are one of the only oceanic dolphins that regularly dive to extreme depths-up to 1,000 meters-to find prey," said William Gough, Marine Mammal Research Program (MMRP) postdoctoral researcher and lead author of the study. "This deep-diving, high-risk foraging strategy requires a delicate balance between the energy they spend and the energy they acquire. Our study is the first step in quantifying that balance for this specific population."

Understanding precisely how much energy the animals require is essential for understanding how to effectively manage against threats and ensure their survival.

"This detailed scientific data gives Hawaiʻi management agencies a critical tool to monitor how changes in the ocean-from warming waters to ship noise-might push the pilot whales past their survival limit," said Lars Bejder, MMRP director and co-author of the study.

The deep waters surrounding the Hawaiian Islands are home to a genetically distinct population of short-finned pilot whales. These highly social, toothed whales are not migratory; they remain with their tight-knit, multi-generational families in one region for life. The population forages year-round where they pursue their preferred prey: squid.

Requirements can inform effective management

"Deep-diving species like pilot whales are especially vulnerable to human-induced disturbances, such as noises from ships or changes in ocean temperature, which can disrupt foraging or increase their energetic costs," said Gough. "If they use more energy than they can find, they face an energy crisis that weakens their health, hurts their ability to fight off disease, and ultimately limits their ability to reproduce and recover the population."

Despite this inherent vulnerability, the Hawaiian pilot whale population benefits from a stable and abundant squid food source, which may better equip them to cope with environmental disturbances than populations elsewhere.

The team placed advanced Customized Animal Tracking Solutions (CATS) tags on eight short-finned pilot whales off the coast of Lānaʻi between 2021 and 2024. The tags recorded movement, depth and sound, and used 2K cameras with LED headlights to observe the whales in their lightless, 800-meter-deep hunting habitat. The researchers developed a new method to estimate minute changes in energy usage by combining data from tags with body measurements from aerial drone footage.

"Getting to be on the water and close to these animals is an absolute joy," said Gough. "But the fact that we can see into their world, even at 800 meters and under extreme pressures [80 times that at the surface], and observe them capturing their food in complete darkness, feels unbelievable to me. It's truly a privilege to document the lives of these elusive, deep-diving whales."

Millions of squid every year

The team analyzed the detailed movement data from the tags to calculate the effort required for swimming and diving, and could then determine the whales' energy requirements. To unravel how much energy they gained from eating, researchers combined two key pieces of evidence: they listened to the rapid clicking sounds the whales make when they try to catch prey, and they analyzed the stomach contents of a stranded whale to learn the types and sizes of their prey.

The resulting model found that an average adult short-finned pilot whale needs to eat roughly 142 squid per day just to break even energetically. Scaling this to the entire estimated Hawaiian population of approximately 8,000 individuals, the total required food intake is roughly 416 million squid (equating to approximately 88,000 tonnes of squid) annually.

Pilot whales are currently listed as "data-deficient" by the International Union for Conservation of Nature, despite having relatively large population sizes. This classification means scientists lack the information they require to accurately assess their risk of extinction. MMRP will apply these scientific methods to estimate the energetic expenditure of other cetacean species, from the harbor porpoise to the blue whale, with the goal of establishing a global benchmark for marine mammal conservation.

This research was funded in part by grants from the Office of Naval Research, the United States Pacific Fleet Environmental Readiness Division, NOAA Fisheries via the Cooperative Ecosystem Studies Unit (CESU), and the United States Department of Defense's Defense University Research Instrumentation Program. Stomach content collection and analysis was funded by the Office of Naval Research and with support of the NOAA National Marine Fisheries Service Johan H. Prescott Marine Mammal Rescue Assistance Grant Program. Satellite tagging field efforts performed by Cascadia Research Collective were supported by multiple sources, including: the Office of Naval Research, United States Navy Living Marine Resources, United States Navy Pacific Fleet, the NOAA Pacific Islands Fisheries Science Center, and a NOAA Species Recovery Grant. Additional funding was provided by the members and supporters of Pacific Whale Foundation and by the Omidyar Ohana Foundation.

B-ROLL:
- Pilot whales swimming
- Pilot whale foraging at depth

SOUNDBITES:

William Gough, UH Marine Mammal Research Program postdoctoral researcher (13 seconds)

"This was one of the first times where we had tags that have LED headlights on them together with all the other sensors, so the fact that we could actually see what we are assuming is a cloud of squid ink was actually really, really cool."

Lars Bejder, UH Marine Mammal Research Program director (9 seconds)

"The fact that pilot whales are removing all these squid from the ecosystem doesn't threaten the squid population as a whole because they reproduce so fast. So that's a great thing."