How are beluga whales responding to Arctic sea ice loss?
15 October 2019
Every spring, two populations of beluga whales migrate thousands of kilometres to the open waters of the Arctic seas north of Alaska to forage during the short Arctic summers. But as Donna Hauser explains, the rapid loss of sea ice and expanding open-water season raises the question: How may this affect the belugas?
The Arctic Seas are not known for their predictability. Beluga whales have encountered highly seasonal, variable and sometimes challenging environments there for millions of years—since at least the Late Miocene period, 23 to 5.3 million years ago. Belugas are known to migrate into areas historically covered with as much as 95 percent sea ice, where they must dive more than 1,000 metres to find food and resurface to breathe in an ever-shifting mosaic of cracks, holes and fractures in the ice.
But unprecedented changes in sea ice, seasonal ice cover, and ice thickness now have the potential to affect not only how the whales use their habitats, but their migrations and behaviours as well.
Teams of researchers have been tagging beluga populations from the Chukchi and Beaufort seas since the 1990s. Thanks to their work, we have access to unique baseline data that can help us understand where the whales are, how they behave, their use of sea ice and ocean habitat, and—more recently—their responses to changes in sea ice.
Using data to get a clearer picture of migration patterns
In the summer, belugas travel and forage across the northern reaches of the Arctic. As the weather cools and their habitats begin to freeze up, they head to the southern areas of their ranges to forage. But in recent years, rising temperatures have meant later freezeups—and researchers have wondered whether this change is affecting the timing of belugas’ migrations. What they have noticed is that different beluga populations appear to have different responses: some seem to delay their fall migration, while others simply continue their usual patterns.
For example, belugas from the Chukchi Sea delayed their fall migration by about 33 days from 2007 to 2012 compared with 1998 to 2002. This delay correlated with a significantly later freeze-up of sea ice in the region. Ultimately, the whales spent more time in their summer foraging areas. It seems these belugas may be coping with a changing Alaskan Arctic marine environment by shifting their migration timing and behaviour.
In contrast, few belugas in the Beaufort Sea seemed to change the timing of their fall migration between the 1990s and 2000s despite later freeze-ups; there was no evidence that the timing of seawater freezing cued their migration. Instead, these belugas seemed to be “pre-programmed” to migrate at a particular time each fall regardless of sea ice conditions. Based on additional research, it seems that sea ice is just one of several predictors of belugas’ summer foraging habitat in Alaska’s Arctic. Conditions that affect their food seem to be more important to these beluga populations.
Changing migration to cope with the changing climate
Broadly, the different responses in migration timing by these two populations tell us that the effects of sea ice changes are not uniform among all beluga whales. But they also make it difficult to discern whether changing migration patterns will benefit or harm them.
For example, shifts in migration timing and diving behaviour by the Chukchi belugas may mean the whales are taking advantage of the greater foraging opportunities that come with the loss of sea ice since staying for more time in the fall means longer access to good foraging. However, tagged belugas from this population have also been observed making significantly longer and deeper dives in recent years, which may indirectly affect their health since it requires considerable energy.
These dives suggest that the whales may have found new prey, or that their usual prey has moved to deeper depths due to changing conditions, such as less ice or warmer water. However, it’s not clear whether changing foraging opportunities can outweigh the extra energy the whales need to sustain these more challenging dives.
It is clear that we need to do more work to understand how beluga whales are responding to their changing environments. As with many Arctic marine mammals, we don’t know whether there has been a shift in the number of beluga whales in these populations, or whether there have been changes in their health and body conditions that might tell us something about the consequences of sea ice loss. So far, this research simply indicates that belugas’ responses to changing Arctic marine ecosystems can vary among different populations.
Hopefully, this flexibility will help them to survive. Meanwhile, it complicates our ability to predict their fate.
DONNA HAUSER is a research assistant professor at the International Arctic Research Center, University of Alaska Fairbanks. Her research focuses on marine mammal ecology, particularly in the context of rapidly changing Arctic marine ecosystems.
Belugas are extremely sociable mammals that live, hunt and migrate together in pods, ranging from a few individuals to hundreds of whales.
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