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Using drones to study the health and body condition of North Pacific humpback whales

Four researchers, outfitted in bright red survival gear, are bobbing at sea aboard a bright orange zodiac on a beautiful day in Southeast Alaska. One is wearing a cumbersome ski helmet, goggles and thick padded work gloves - an unexpected clothing choice for traveling on the water. However, the reason for the protective gear becomes clear as the researcher lifts a sleek-looking Unoccupied Aerial System (UAS) with four, fast-spinning propellers over her head.

“Three, two, one, go!”

She releases the UAS - or “drone” - into the air and watches as it rises, hovers for a moment, then zips towards its target: a humpback whale that’s swimming just below the surface several hundred yards away. Meanwhile, the drone pilot, Martin Van Aswegen, is glued to a video feed that’s broadcasting from the drone to his handheld controller. He steers the drone to where the whale was last seen and stops to hover 100 feet or so above the water, its buzzing no longer detectable over the humming of the boat engine and the lapping sounds of the ocean waves. After several moments of waiting, the whale surfaces, its body visible and outstretched. “Got it!”, he says, as he gives the team a small nod and begins navigating the drone back towards the boat. Van Aswegen, together with the rest of the AWF field team, just successfully captured a humpback whale “body condition” image - an important data point in AWF’s efforts to track the health of Alaska’s whales.

Researchers with AWF launch drones from their research vessels using protective gear to protect their hand and hands. A live feed video is recorded and broadcast to a handheld recorder that allows the researcher to control the drone.


Van Aswegen joined AWF’s field team in 2018 to help assess the feasibility of using drones to measure the size and body condition of humpback whales as part of a collaborative effort between AWF and the University of Hawaii’s Marine Mammal Research Program (MMRP). Prior to arriving in Alaska, he had been living in Western Australia and was excited for the change of scenery. Exploring the US’s northernmost state had always been a dream of his; the final frontier seemed so far away and different from the hot, dry and flat Australian landscape.

“I showed up at the AWF field station with a pair of old jeans, flip flops and no rain jacket,” Van Aswegen recounts of his first day at the field station. “Looking back now, I was woefully unprepared for the potentially unforgiving elements of Southeast Alaska.”

Beautiful view of Warm Springs Bay from the Alaska Whale Foundation field station.

After a successful first season, Van Aswegen was invited back to Alaska as part of his new PhD program with MMRP. Little did he know at the time how tightly linked his next several years would be to the seasonal movements of North Pacific humpback whales.

Humpback whales are migratory: each year, they travel between summer feeding grounds, like Southeast Alaska, and low latitude winter breeding grounds. Given the vast distances between the feeding and breeding grounds, and that most humpback populations straddle international boundaries, individual research teams rarely study whales on both ends. However, most of Southeast Alaska’s humpbacks winter in US waters - the Hawaiian islands. With AWF’s partnership with MMRP, the stage was set for Van Aswegen to participate in one of the largest whale health projects - in terms of spatial scale and the sheer amount of data that it yields - on the planet. For Van Aswegen, this would mean traveling ~3,000 miles each spring and again each fall to collect body condition images on both ends of the whales’ migration.


So why is a whale’s body condition important? Body condition, or more accurately body volume, reflects a whale’s energy reserves - essentially, its blubber stores. The amount of blubber a whale has carries important implications for its growth, health and reproductive success. As well, because humpback whales depend on prey near the base of the food web, such as krill and small schooling fish, a population’s average body condition can serve as a sensitive indicator of the overall health of its surrounding ocean ecosystem.

The health of ocean ecosystems became particularly concerning in late 2013 when researchers working throughout the North Pacific began detecting a troubling rise in ocean temperature. For the next few years, one of the largest and most persistent marine heatwaves on record wreaked havoc throughout the North Pacific. This event - the “blob”, as it became known - was characterized by abnormally warm waters from the surface to as deep as 300m in some areas. Warm waters tend to be nutrient poor, so many species struggled to acquire enough food, leading to widespread mortality up and down the North Pacific marine food web. For humpback whales, researchers across the North Pacific began observing marked declines in mother-calf sighting rates in Hawaii and unusually high calf mortality in Southeast Alaska. Moreover, a shockingly high number of whales appeared skinny and emaciated. It was observations like these that led the AWF and MMRP team to begin tracking and quantifying whale body volume.


Historically, measuring the size of a free-ranging whale has been difficult. However, recent advances in drone technology are making this not only possible, but surprisingly efficient. To measure a whale, researchers capture high resolution images of it as it surfaces. With knowledge of the drone camera’s field of view and its distance from the whale provided by an onboard laser rangefinder, the whale’s body length and width at regular intervals along its body can be calculated. These measures can then be used to estimate the whale’s body volume - a proxy for blubber volume - with such accuracy that increases or decreases in volume over only a few days can be observed.

When Van Aswegen first learned about this “aerial photogrammetry” technique, he was hooked.

“It represented the amalgamation of my two passions – wildlife photography and ecological research.”

Equally rewarding for Van Aswegen has been the opportunity to see the same individual whales year after year and across a vast ocean basin. One example is a well-known mature female, known locally as Defenestration, who was first observed in the 80s. Van Aswegen has observed her every year in both Southeast Alaska and Hawaii since he started collecting data in 2018. During this time, he has quantified her body volume while pregnant, with a calf, and while resting - i.e., taking a year off from breeding. A surprising result from these data is that, despite feeding intensively in Alaska, female humpback whales continue to lose body volume across the summer while lactating. This highlights the high energetic costs to females that come from raising a calf.

The AWF team uses a technique called photogrammetry to measure the body size and condition of as many whales as possible through their summer field season. This is an example of an aerial image used to measure whale length and body width (in 5% increments).


Ultimately, Van Aswegen aims to use his drone data to quantify how humpback whales’ body volume - and the rates at which they gain or lose body volume - differ between sexes, reproductive states and age classes. He is also looking to quantify the energetic costs to the whales of migrating and breeding by estimating the volume of blubber that they lose between leaving Alaska in the fall and returning the next spring. Perhaps most importantly, he aims to shed light on how whales will respond to future warming events. Climate scientists and oceanographers predict that marine heatwaves, like the one that prompted Van Aswegen’s study, will increase in their frequency, duration, and severity as the planet warms. It is therefore vital to determine how the health of top predators like humpback whales will be impacted by these environmental stressors.

With these important questions looming, Van Aswegen has his work cut out for him. However, 2023 marks a change in his schedule. The time has come for Van Aswegen to focus solely on analyzing his massive dataset and begin writing the chapters that will form his PhD dissertation. This means he will not join the whales in Alaska, something that he will miss.

“As nice as Hawaii is, I do miss the crisp cool air, snow-capped mountains, and awakening ecosystems characteristic of spring in Southeast Alaska. No doubt the brown bears are waking up, migratory birds are showing up, and the temperate rainforests are coming back to life following winter. I’m hoping I get a chance to go back to this amazing environment”. If and when he does, Defenestration and all the other whales he has come to know will be there to greet him.



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