The narwhal, often called the “unicorn of the sea” for its distinctive spiraled tusk, is a toothed whale living exclusively in the Arctic waters of Canada, Greenland, and Russia. This species undertakes one of the most extensive migrations of any marine mammal, partitioning its annual cycle between coastal summering grounds and offshore wintering areas. Their movements are driven by the seasonal formation and retreat of Arctic sea ice, which dictates their access to food and shelter.
The Seasonal Cycle: Summer Habitat
From June through September, narwhals congregate in shallow, ice-free coastal waters. They exhibit strong fidelity to these summering grounds, returning year after year, often to the deep fjords and inlets of the Canadian High Arctic and West Greenland. These locations offer a protected environment important for critical life stages.
The primary purposes of the summer habitat are reproduction and the formation of large aggregations, or pods, which can number from a few dozen to over a thousand individuals. While narwhals feed sparingly compared to winter, their diet shifts to take advantage of the seasonal bounty of smaller, pelagic prey, such as Arctic cod and capelin.
Females give birth to a single calf after a gestation period of about 14 months, with most calving occurring between June and August. The shallow, isolated inlets provide a safe place for newborn calves to nurse and rapidly develop blubber before the winter migration. Calves remain dependent on their mothers for nearly two years, learning complex migratory routes and survival skills.
The Deep Dive: Winter Habitat and Ice Coverage
As autumn progresses, narwhals shift to their wintering grounds in deep, offshore waters, such as Baffin Bay and Davis Strait. This habitat is characterized by dense pack ice, often covering 90 to 99 percent of the surface. They spend up to six months under this thick ice, surviving by using small, temporary openings known as leads and polynyas to breathe.
The narwhal is one of the deepest-diving marine mammals, capable of reaching depths exceeding 1,500 meters. They routinely perform dives to at least 800 meters, sometimes up to 25 times per day, in search of food. These extreme dives target deep-water, bottom-dwelling prey, with the Greenland halibut being a primary food source in the cold depths.
Narwhals consume the majority of their annual food intake during these winter months under the ice. This intensive foraging behavior is necessary to build up the fat reserves needed to survive the rest of the year. The dense ice cover provides protection, as the large dorsal fins of their main predator, the Killer Whale, prevent them from penetrating the pack ice effectively.
The Mechanics of Movement
The timing of the narwhal’s migration is directly linked to the seasonal cycle of sea ice formation. They depart their summer grounds in late September or early October, traveling hundreds to over a thousand kilometers to their wintering areas before the coastal “fast ice” locks up the fjords. The autumn migration is a directed, faster journey, driven by the need to reach deeper offshore waters before the ice completely closes off their path.
Conversely, the spring migration, which begins around May or June, is slower as the whales move north, following the breaking and retreating ice edge back to the coastal areas. The primary drivers of this long-distance movement are the search for specific prey and the avoidance of predators. The narwhals follow the seasonal distribution of the Greenland halibut and other deep-water fish.
The dense winter ice acts as a protective shield, but the whales must move as the ice breaks up in spring, which allows predators like orcas to enter their winter territory. Their migratory routes are not uniform, with some populations traveling along the coast and utilizing specific rest and feeding stopovers, while others take a more direct, offshore route. This migratory fidelity highlights a deeply ingrained survival strategy.