In the spring of 1999, a University of Saskatchewan biologist tracking polar bears on Lancaster Sound, north of Baffin Island, discovered a group of more than two dozen bears gathered around a cluster of swimming pool-sized air holes in the solid sea ice. The holes turned out to be the only lifelines for some 75 whales that had been trapped more than 30 kilometres from open water by a sudden advance in the ice edge.
Beluga whales fighting for air in a tiny sassat near Lancaster Sound, Nunavut. Photo: Malcolm Ramsay.
Although the Inuit have long known about this unique polar phenomenon, which they call a sassat, the entrapment of whales in Arctic sea ice is rarely witnessed because the air holes are so difficult to spot, especially from the air. The events appear to take place in early spring, when whales enter areas of unconsolidated or loose pack ice in search of food. Because ice concentrations in these packs are already about 80 per cent, certain conditions can cause them to solidify or consolidate very quickly, leaving the whales stranded without sufficient breathing holes to reach the open ocean. Forced to enlarge existing holes and remain there until the ice breaks up, they become easy prey for polar bears and Greenland sharks.
Last fall, the University approached Environment Canada's Canadian Ice Service to help determine precisely when the Lancaster Sound sassat occurred and to identify the conditions that cause late season ice edge surges. The collaboration is an important step toward understanding how frequently these events occur, and the mysterious relationships between ice-associated animals and sea ice conditions. By understanding these linkages, scientists hope to determine the potential repercussions of climate change on sea ice formation and animal populations. For example, if global warming causes sea ice to begin melting earlier and forming later, polar bears may have less time to forage for food, but might benefit from increased opportunities for sassats.
Using satellite imagery collected for the operational ice forecasts they provide to the shipping industry, ice experts narrowed the date of the sassat down to three or four days in mid April by monitoring changes in the ice edge. Additional meteorological information helped them pinpoint April 16 as the most likely date of the event, because that was when a high pressure system brought very cold temperatures and winds from the northeast, which pushed the unconsolidated pack ice up against the ice edge. They estimate that the ice advanced about 30 kilometres in less than 48 hours, and that the sassat lasted about 60 days.
As the first sassat studied by Canadian biologists, the Lancaster Sound event yielded some interesting information. Four bears tranquilized at the site proved heavier than the heaviest specimens ever measured in their age and sex classes in more than 10 years of study proving that the bear exploit this phenomenon heavily and in a short period of time. The whales were also significantly affected, with a number badly injured or killed as a result of attacks suffered from below and above, as they surfaced to breathe. Although the whales represented less than one per cent of the local beluga population, the potential impact of several events each year could be significant. Of even greater concern is the fact that one of the whales involved was an endangered bowhead. Observations made at the site also offered the first evidence that Greenland sharks prey on live whales.
This spring, ice scientists have stepped up their monitoring of the ice edge and meteorological data to identify potential entrapment conditions-including calm conditions with very low temperatures, and storms that break up the ice edge, making it possible for it to re-consolidate later. They also plan to examine the conditions surrounding a similar incident near Grise Fiord, 100 kilometres north of Lancaster Sound, that also occurred in the spring of 1999. By using their knowledge of how, when and why sea ice forms to assist biologists in locating sassats for further study, Environment Canada's ice scientists are greatly improving our understanding of the biological significance of this little-known phenomenon.