Whale data collected to find out ‘what’s going on’
Researchers look at reasons behind whale declines, impact of heatwave
MAALAEA — To understand “what’s going on” with declines in observed humpback whale sightings as they migrate between Hawaii and Alaska, a band of researchers is taking a deeper dive into the overall health and energy levels of the whales and comparing data between pre- and post-heatwave behaviors.
After the Great Whale Count showed a 64.5 percent decline in humpbacks during the 2015-16 season, three researchers partnered to study whale body condition, as well as their feeding and breeding patterns from year to year.
This “can tell us a lot about the changing trends in humpback whales,” said Jens Currie, chief scientist at Pacific Whale Foundation, on Tuesday night at Maui Ocean Center’s The Sphere.
“It’s going to be a cumulative effect from a lot of things that are happening,” Currie said. “But for now, if any sort of decline happens again, we have more data to answer that question more quickly.”
Hawaii island also saw a drop (57.1 percent) in the same season after shoreline-based scans, with a bigger decline in calves, specifically. Alaska’s photo-ID survey reflected a 51 percent decline and reported skinnier whales between 2016 and 2018.
During the Maui Nui Marine Resource Council’s “Know Your Ocean Speaker Series,” Currie started the presentation with a brief discussion about possible reasons for the declines, several related to warming of the oceans.
There were El Ninos, large-scale periodic warming in sea surface temperatures across the central and east-central Pacific Ocean, in 2012 and 2017; the Pacific Ocean heatwave between 2013 and 2016, also known as the “Blob,” covering about 4 million square miles; and the Pacific Decadal Oscillation, a long-term ocean warming cycle that occurs primarily in the North Pacific that can cause changes in the food chain.
Peak humpback whale seasons were happening earlier and not lasting as long, Currie said, adding that this is not the case this year.
Currie’s team will be studying five main areas: distribution or migration patterns, abundance, prey distribution and quality, environmental and human stress and population health. Population health can be understood by studying the relationships between body measurements and condition; individual characteristics; and steroid hormone, lipid and stable isotope levels.
“The overall goal is to increase the assessment efforts of humpback whales’ conditions here in Hawaii and Alaska,” he said. “They need the energy to come to Hawaii, that’s the first step, but they also need the energy to partake in the breeding ground activities.”
Lars Bejder, director of the Marine Mammal Research Program at the Hawaii Institute of Marine Biology at University of Hawaii-Manoa, said researchers are able to quantify energy levels and health by using noninvasive suction cup tags and unmanned aircraft systems or drones and through fieldwork.
Starting in 2018, the devices have collected data on speed; depth; movement; and body condition, including skin, size, length and mass; as well as feeding rates in Alaska and birth rates in Hawaii.
Using the same methods, Bejder said scientists also are studying why Australia has experienced an 8 to 10 percent increase in whale populations.
“If we have measurements now, then we’ll be able to compare them to other populations” and explore links between large-scale heatwave events, he said.
Bejder’s focus is on the bioenergetic model — how cells transform into energy — in males, calves and mothers to understand “how much it costs” to migrate.
“The bigger, stronger, healthier you are, the more likely you are to reproduce,” he said. “So if you’re able to quantify the health of an organism based on body size, you can say something about its population.”
The trip from Alaska after feeding is about 6,000 miles, and whales don’t feed again for four months while they travel and breed in the islands, Bejder said. This causes “pressure on these mammals” to find the nutrition they need.
The body condition of humpback whales changes while in Hawaii, Bejder said. Energy, hypothetically, is depleted upon reaching Alaska, which then increases after feeding, and then drops again during their fasting, migrating and breeding time.
Adults range in length from 35 to 55 feet and weigh 25 to 30 metric tons. By the time the humpbacks leave Maui, they have lost, on average, a third of their body mass.
“Whale residency in the Hawaiian Islands is dependent on body composition during fasting and reproductivity,” said Adam Pack, professor at the University of Hawaii-Hilo. “It’s important to understand the types of stresses that occur between Alaska and Hawaii.”
The next steps in their research include studying biopsy samples and blubber histology, which assesses body condition using blubber adipocyte area index. This will help gauge fertility rates in females; how stress can impact reproduction and the immune system; and testosterone levels.
After partnering with the Pacific Whale Foundation in 2019, Pack said researchers collected 25 samples last year and another 33 in January, with more to come in March.
Pack’s work also will focus on documenting energy expended during male competition for mating opportunities, which is “getting harder and harder to find because the females are leaving, so the males switch over to the mothers, so we start seeing these large competitive groups later in the season.”
Mothers are expending more energy and experiencing more stress when there are more escorts around. As a consequence, they are displacing themselves from the group and swimming in shallower waters, he said.
“What we’re interested in, is establishing some baseline levels of stress of humpback whales,” Pack said. The idea is to go back, prior to this heatwave, and compare stress levels.
“Through all these studies, our goal really is promoting healthy central Pacific populations of humpbacks for all future generations and to recognize that we are a community here, and we have social networks that are important to us,” he said. “We are the stewards, and we need to protect the whales for future generations and their social networks.”
* Dakota Grossman can be reached at firstname.lastname@example.org.