When you think of the work of a marine biologist, shooting whales is probably not the first image that springs to mind.
But for Susan Bengtson Nash from Griffith University’s Humpback Whale Sentinel Program, a rifle is a key tool in her fieldwork arsenal.
This is how she and colleagues collect samples from humpback whales:
“We fire [modified darts] at the dorsal area of the whale [and] the recoil of the dart causes it to bounce off,” says Associate Professor Bengtson Nash.
The darts penetrate the whale skin and blubber, collecting the samples, before bouncing back into the water where they float until collected by the researchers.
The samples provide important clues about the health of the Antarctic sea-ice ecosystem, which the Humpback Whale Sentinel Program aims to monitor.
Overcoming the challenges of Antarctic research
But conducting scientific research in Antarctica’s once-pristine environment is extremely difficult: the number of scientists allowed to visit each year is limited, the weather conditions are extreme, and it’s expensive.
In 2020, the number of visiting researchers was especially low due to the COVID-19 pandemic.
As a result, some research projects will have gaps in their data — an entire year or more where they don’t have observations.
To get around these problems, researchers in the Whale Sentinel Program collect whale-blubber samples from humpbacks during their northerly migration.
Humpback whales spend the summer feeding in Antarctic waters before migrating north to breeding grounds in warmer waters.
So, each winter Dr Bengtson Nash and colleagues in places like Colombia, New Caledonia, Brazil and Western Australia have been visiting humpback-whale breeding grounds in their local area to collect samples.
These samples serve as a proxy for what is going on in the frigid waters to the south.
Fat cell size and pollutants give clues to whale health
The team now has 13 consecutive years of whale data from contributors to the program.
And although the individual blubber samples are small, the amount of information they can deliver is vast.
For example, the size of the fat cells in the blubber shows how much energy the whales managed to store during the Antarctic summer.
Analysis of isotopes and fatty acids gives information on where their food — predominantly krill — has come from.
And the concentration of persistent organic pollutants is also used as a measure of how much fat the whales have in reserve.
Meanwhile, steroid hormones can be used to identify the number of pregnant females making the migration, according to Dr Bengtson Nash.
“If they’re low on food stores, the females are probably thinking ‘I’m not going to go on the migration this year, I’m going to stay where the food is’,” she says.
Whale health signals changing sea ice
The researchers correlated their analysis of the whale blubber with environmental data collected in Antarctica itself.
And they found evidence that humpback whales are “powerful Antarctic sea-ice ecosystem sentinels“.
“The first signal we got was in 2010/11 — it was the strongest La Nina event on record,” Dr Bengtson Nash says.
There was reduced sea ice and changes to phytoplankton in the whale feeding grounds.
Following that season, the whales came up in poor body condition, and they also seemed to switch diet.
“It seemed to show they moved away from Antarctic krill,” Dr Bengtson Nash says.
The next strong signal that Antarctica had experienced extreme climate conditions was six years later.
“So, we go back to our environmental data and oh look, 2017 was the worst year for sea ice on record,” Dr Bengtson Nash says.
Since then summer temperatures have become more extreme, exceeding 20 degrees Celsius on the Antarctic Peninsular for the first time in 2019/20.
Researchers are not sure how poor sea ice levels are linked to poor whale health, but there are some clues that krill is playing a major role.
Krill’s key role in Antarctica
Research has shown krill larvae use sea ice to shelter from predators and as a means of transport to food-rich waters, which means their distribution is expected to change as sea ice is reduced.
So Kawaguchi, a krill ecologist with the Australian Antarctic program, says climate change scenarios forecast the northern range of krill will contract southwards as waters warm.
Dr Bengtson Nash says while Northern Hemisphere humpback whales appear to be able to adapt to life without krill, a crash in krill could have huge repercussions for the Antarctic ecosystem as a whole.
“Antarctic krill are what we call the keystone species. Everything depends on krill,” she says.
According to Dr Kawaguchi, scientists estimate krill biomass to be equivalent to the total weight of human beings on the planet.
“You can easily imagine how the dynamics of this single species may cascade through the entire Southern Ocean ecosystem,” he says.
As well as being a food source for the whales, Antarctic krill help to sequester atmospheric carbon dioxide, he said.
“Krill consume enormous amounts of phytoplankton and turn them into fast-sinking faecal pellets.”
Scientists are still trying to work out exactly how climate change will impact krill populations, and the effects are likely to vary regionally.
According to Dr Kawaguchi, though, it won’t be all bad news.
“I do think the ecosystem is resilient, so the system will adapt to a new norm, but its structure will certainly change — there will probably be winners and losers,” he says.
Dr Bengtson Nash thinks the humpbacks may adapt, but they may be the canary in the coal mine for bigger changes in the south.
