The largest summering population of beluga whales is found in Hudson Bay.

Credit: Oceans North

Each summer, an estimated one-third of the world’s belugas migrate to the shallow estuaries of the Churchill, Seal and Nelson rivers of western Hudson Bay to feed and raise their calves. A new study has found that, rather than congregating in distinct groups, belugas with calves moved throughout the Churchill and Seal River estuaries to raise their offspring during the summer months. The findings support the need to protect wide swaths of marine habitat in western Hudson Bay.

In some populations, belugas segregate themselves, with older males separate from females and immature males. But the study found that belugas with calves mixed with adults and juveniles throughout the Churchill and Seal River estuaries. This behaviour could not be attributed to any environmental factors such as sea surface temperature, water depths or distance from shore.

“Belugas are very social so that could be what’s driving their distribution,” said Kristin Westdal, a co-author of the study and Arctic field research director for Oceans North. “This means it’s important to protect the entire area because belugas with calves are roaming widely within it.” Oceans North has long supported the creation of a national marine conservation area in this region to protect these whales from the threats of declining sea ice, increased predation by killer whales and industrial development.

The study, released in pre-print earlier this month, was based on photographic data of belugas collected during Fisheries and Oceans Canada (DFO) aerial surveys of these estuaries during August 2015. Calves can be identified because they are 30 to 50 percent smaller than adults, while juveniles are grey and 50 to 75 percent the size of adults. A total of 13,538 belugas were counted in the river plumes of the Churchill and Seal River estuaries, with calves making up between 4.25 percent and 6.6 percent respectively of the total population.

The other two co-authors on the study, which will be published following peer review in PlosOne, were Jeremy Davies, a marine spatial expert with Ocean Conservancy, and Steve Ferguson, a University of Manitoba professor and Research Scientist at Fisheries and Oceans Canada.

Ruth Teichroeb is Oceans North’s communications director.