TWS2020: Where do belugas spend their summers?

Beluga whales are likely choosing where to spend their summers in estuaries based on the prey available, researchers found.

The western Hudson Bay is home to the largest known population of belugas in the world — between 55,000 and 60,000 of them. They return to estuaries in the Hudson Bay every summer, with high concentrations in the Churchill, Seal and Nelson estuaries.

“Why do they come to these estuaries?” said TWS member Emma Ausen, a master’s student at the University of Manitoba, in an oral presentation at the virtual Annual TWS Conference. “It’s not exactly known.” Ausen figured it may have something to do with the waters being beneficial to the whales’ growth, that it’s good for molting, that shallow estuary waters provide predator protection or that there’s a good source of prey there.

With climate change — and melting sea ice — altering the region, it’s especially important to know more about the beluga (Delphinapterus leucus), a species of special concern under the Committee on the Status of Endangered Wildlife in Canada, Ausen said. “The climate is warming, which is making access to the Arctic way easier for development and shipping vessel seasons,” she said.

Ausen and her colleagues investigated which environmental and habitat features best describe beluga habitat use in the estuaries of the western Hudson Bay. They used a photographic aerial survey take in 2018 from helicopter flights to answer their questions.

Overall, she and her colleagues observed 1,332 belugas from the aerial survey. They then looked at habitat features based on their theories about why belugas would choose estuaries. Some of those habitat features included sea surface temperature, nutrient availability, sediment content, distance to the river mouth and distance to shore.

They looked at what habitat was available versus what habitats the belugas were choosing. “For the full western Hudson Bay area, the variables selected were distance to river mouth and total suspended sediment content,” she said, both of which are related to prey availability.

For the Nelson estuary, Ausen said all of the variables were important for determining distribution of belugas. But for the Seal and Churchill estuaries, sea surface temperature, distance to river mouth and sediment were the most important.

Overall, they found that the availability of these habitats is lower than what the belugas are selecting for. For example, overall sediment only makes up 36% of the habitat, but is selected for over 60% of the time by belugas.

But Ausen said there’s more to learn and potentially better variables out there to represent whether belugas are, for example, coming to estuaries to avoid predators or for molting. “We don’t have a complete picture of what’s happening,” she said.

But their research does show that sediment and distance to river mouth were important in all models.

“This research can give us a better understanding of what habitat is important for beluga use of estuaries and can contribute to estuary use theories and what we know about belugas in general,” she said. “It can also provide a baseline of beluga habitat in the western Hudson Bay. Habitat is changing, so it’s important to know what’s going on now as we go forward with climate change.”

Conference attendees can visit office hours for this contributed paper on Wednesday, Sept. 30 from 3 to 4 p.m. to learn more and ask questions.