Federal fisheries scientists have been studying beluga whales in Hudson Bay, where changes to sea ice may have led to dropping mercury levels in some female whales but an emerging threat from another whale species.

Although killer whales have been spotted in Hudson Bay since the 1950s, people in area communities have reported seeing more of them in recent years, said Steve Ferguson, a research scientist with the federal Department of Fisheries and Oceans.

Ferguson, who works in the department's Arctic aquatic research division in Winnipeg, said he is analyzing hormone levels from beluga whale samples to determine how the belugas are reacting to the rising killer-whale threat.

"The indication is that the killer whales are there a little longer, now there's less sea ice, and maybe they're doing a little more attacking on the beluga," Ferguson told CBC News.

"We're taking samples from them [belugas] to see if they're finding it more stressful recently, trying to live with killer whales around that are trying to kill them and eat them."

Mercury levels down 32% in females

Ferguson's research complements work being done by fellow DFO research scientist Gary Stern, who has found mercury contaminant levels have gone down in female beluga whales in Hudson Bay.

Stern found that methyl mercury levels in the muscle tissue of female beluga whales harvested in Arviat, Nunavut, have dropped by 32 per cent between 1984 and 2008.

Longer ice-free periods on Hudson Bay could be affecting what and where the whales are eating, as the female belugas may be eating less contaminated prey that are found in offshore areas, Stern said.

"In Hudson Bay, if they feed more offshore — which they seem to be doing — we find that the levels of mercury, for example, in Arviat in the female animals have actually been declining over time, which is good news," he said.

As for why lower mercury levels have been detected in female whales, but not males, Stern said predators may be a factor: female whales may eat offshore, where there are fewer threats to their young, he said.