Using the data collected from the transmitters, Laidre has learned that narwhals are true creatures of habit. Many of the narwhals’ biological patterns—when they eat, migrate, and reproduce—are orchestrated in tandem with the annual expansion and retreat of Arctic sea ice.

In the summer, retreating ice allows narwhals and their newly born calves to access their summering grounds in the sheltered inlets, bays, and fjords along the Canadian Arctic coast and northwest Greenland. As fall begins and the coastal summering grounds begin to freeze over again, the narwhals move out and migrate southward.

By mid-November, large populations of narwhals are gathered in the offshore areas of Baffin Bay and Davis Strait where Greenland halibut—their main food source—are plentiful. Narwhals spend the winter in this region, virtually surrounded by dense winter pack ice, and diving to feed on halibut near the sea floor.

“The pack ice in winter works like a conveyer belt, forcing the animals to constantly move,” Laidre says. “The narwhals have the largest ranges and highest velocities during years with extensive ice cover.”

A recent expedition gave Laidre an even greater appreciation of how challenging it is to survive in this winter habitat. In 2008, Laidre and her colleagues flew over the narwhal wintering grounds in a Twin Otter plane. They recorded their own narwhal sightings from the aircraft, as well as sightings documented by video recorders and digital cameras. They estimated that there were approximately 18,000 narwhals in their survey region. Most of that area, however, was covered in dense ice, and only two percent was open water available to narwhals for breathing.

A lone narwhal is spotted in this image captured by a survey plane that Laidre and her colleagues flew over the wintering grounds. In this extreme environment, the narwhal is surrounded by ice of various densities. Image courtesy of Kristin Laidre.

Narwhals are mammals and need air to survive, so they tightly pack themselves in stretches of open water and cracks—called “leads”—in the lighter, newer ice. The researchers estimated that about 77 narwhals were clustered below every one square kilometer of open water in the survey region.

The frozen landscape can shift quickly; changes in ocean currents, winds, and temperature can cause leads to open up and then refreeze again rapidly.

Recently, even larger changes have been taking place in the narwhals’ wintering grounds. Satellite data have revealed a 9 to 11 percent decline in sea ice extent per decade in the Baffin Bay and Davis Strait areas since 1979. Scientists have also documented the earlier springtime breakup of ice in Baffin Bay.

Northern Baffin Bay begins to freeze up in early November, and by the end of November most of the bay is typically covered with sea ice. The maps at left show where sea ice was present in at least 9 out of 10 years (white) on November 15 during two decadal periods: 1982-1991 (top) and 2002-2011 (bottom). Large areas where sea ice was typically present in the early decade are ice-free in the most recent decade, illustrating the delay in autumn freeze-up. Map based on sea ice concentration data from the National Snow and Ice Data Center, and calculations by H. Stern, University of Washington. Credit: NOAA climate.gov

“The whales are used to living in the pack ice during the winter,” Laidre says. “We don’t yet know what they will do if, in the future, the ice isn’t present where it normally is.”

While sea ice loss would create more open water space for the narwhals, shifts in the melting and freezing cycles may alter their migratory, feeding, and reproductive patterns. Changes in the ice regime could also directly translate to changes in the Arctic ecosystem that could indirectly harm the narwhals.