By Stephen Petersen
Stephen Petersen is the Director of Conservation and Research for Assiniboine Park Zoo. He has been studying Arctic marine mammals for most of his career and has been conducting research in Churchill for ten years.
The first time I saw ringed seals in Churchill I was driving along the Hudson Bay coast from the airport to the Churchill Northern Studies Centre. At first glance, all I saw were black blobs peppering the sea ice attached to the shore. Through my binoculars, those blobs came to life revealing hundreds of seals lazily basking in the bright sun. That first glimpse into the lives of these fascinating creatures had me hooked—and it led me to study these and other seals for ten years … and counting.
Churchill is an exciting area for a seal biologist because it is a crossroad for several ecosystems: from marine to terrestrial, saltwater to freshwater, and ocean to river. It is also home to a pair of seal species ideal for monitoring and contrasting the effects of climate change.
In total, Hudson Bay is home to five species of true seals (Phocidae). Two species, the harp seal and hooded seal, only occupy the northern part of the bay. The other three species, all of which can be observed along the Manitoba coast, are the ringed seal, harbour seal, and bearded seal. Bearded seals are the least common of the three around Churchill, where they can occasionally be seen in summer and autumn.
The two other species are the easiest to monitor. Ringed seals are most abundant in the area, observed most readily on the sea ice in the spring. Harbour seals are present throughout the open-water season, in local rivers and coastal areas.
Interestingly, ringed and harbour seals are both found in the same general location but have very different approaches to survival in the Arctic and sub-Arctic. One of these species’ survival strategies appears to equip it better than the other for impacts of climate change. Which species? To find out, we must first follow them through a few critical times of the year.
The primary survival hurdle for air-breathing Arctic marine mammals is to live through the winter, when ice covers almost everything.
Above: Ringed seals on the spring sea ice of Hudson Bay near Churchill (Photo courtesy of Stephen Petersen)
Ringed seals tackle this challenge by using their front claws to create and maintain breathing holes in ice up to 1.5 meters thick. When sea ice starts to form on Hudson Bay in the fall, adult ringed seals set up territories in the “land-fast” ice that forms along the coast and is stuck fast to the land. Snow that falls during the winter accumulates in drifts and provides the ideal place for seals to dig dens that protect them from the elements ... and hopefully polar bears, who depend heavily on ringed seals for survival. The stable land-fast ice is also favoured by females as denning habitat where they can birth and nurse their pups.
Female ringed seals give birth in the spring and nurse their pups for about 40 days with energy-rich milk. During this time, they are at risk of polar bear and Arctic fox depredation but tend to be protected until the snow and sea ice melt. The naive, young seals have a steep learning curve in their first year, as evidenced by the fact that polar bears can gain most of their yearly weight hunting them in the spring. In years with less snow, or when unseasonal rainfall events expose dens, ringed seals are more exposed to polar bears and pup survival is lower—reaching as high as 100% mortality when no snow accumulates in warm years.
So how does an animal who relies so heavily on snow cover deal with a warming climate that turns the thermostat up earlier each spring? The answer: not so well.
Harbour seals, on the other hand, may be able to take advantage of these changing conditions thanks to their differing survival strategies. At first, harbour seals may sound worse off than ringed seals in the Arctic because they don’t maintain breathing holes or give birth in protective dens. However, they simply navigate the Arctic’s obstacle course differently.
Above: Harbour seals in the summer, hauled out on rocks in the Churchill River. (Photo courtesy of Stephen Petersen)
First, they move to areas where winds and currents keep the ice in constant motion, forming cracks and leads through which they surface to breathe. Although this also puts them at risk of being detected by hungry polar bears, harbour seals in Manitoba still persist along the outer edge of land-fast ice, where an ice crack known as the “floe edge” predictably forms each winter.
Harbour seals also give birth later in the year than ringed seals; around the end of May to early June in Churchill. This makes the weather much more hospitable for young pups who are raised without dens.
In addition, harbour seals are also known to leave the bay, hauling out onto land and swimming far upstream in certain rivers. In the Churchill area, they move into the river as soon as there is a crack in the ice wide enough for safe passage. In years when the ice breaks up earlier, pregnant females can avoid polar bears while they give birth and nurse their young, giving them a major advantage over ringed seals.
So between these two seal species, which one could be less impacted by climate change? In the areas where I study them and during the seasons when I observe them, harbour seals appear to be doing better. Spring counts of harbour seals in the Churchill River increased from less than 50 to a minimum of 140 individuals between the late 1990s to 2016, which is a period that coincided with an earlier breakup of winter sea ice in that part of Hudson Bay.
Will this advantage persist? That is yet to be determined. But I do know where I will be as this story plays out: somewhere along the Churchill River or Hudson Bay coast, binoculars in hand.