Behavior and Diet
Narwhals have a relatively restricted and specialized diet. Their prey is predominantly composed of Greenland halibut, polar and Arctic cod, cuttlefish, shrimp and Gonatus squid. Additional items found in stomachs have included wolffish, capelin, skate eggs and sometimes rocks, accidentally ingested when whales feed near the bottom. Due to the lack of well-developed dentition in the mouth, most prey is swam towards until it is within close range and then is sucked with considerable force into the mouth. It is thought that the beaked whales, who have similarly reduced dentition, also suck up their prey.
Narwhals are a migratory species. As spring comes, these leads open up into channels and the narwhals return to the coastal bays.
Narwhals exhibit seasonal migrations, with a high fidelity of return to preferred, ice-free summering grounds, usually in shallow waters. In summer months, they move closer to coasts, usually in pods of 10-100. In the winter, they move to offshore, deeper waters under thick pack ice, surfacing in narrow fissures in the sea ice, or leads. Narwhals from Canada and West Greenland winter regularly in the pack ice of Davis Strait and Baffin Bay along the continental slope with less than 5% open water and high densities of Greenland halibut. Feeding in the winter accounts for a much larger portion of narwhal energy intake than in the summer and, as marine predators, they are unique in their successful exploitation of deep-water arctic ecosystems.
Most notable of their adaptations is the ability to perform deep dives. When on their wintering grounds, the narwhals make some of the deepest dives ever recorded for a marine mammal, diving to at least 800 meters (2,625 feet) over 15 times per day, with many dives reaching 1,500 meters (4,921 feet). Dives to these depths last around 25 minutes, including the time spent at the bottom and the transit down and back from the surface. In the shallower summering grounds, narwhals dive to depths between 30 and 300 meters (90–900 feet).
Narwhals normally congregate in groups of about five to ten individuals, sometimes up to 20 outside of summertime. Groups may be "nurseries" with only females and young or can contain only post-disperal juveniles or adult males ("bulls"), though mixed groups can occur at any time of the year. In the summer, several groups come together, forming larger aggregations. Such aggregations can contain from 500 to over 1000 individuals. At times, bull narwhals rub their tusks together in an activity called "tusking". This behavior is thought to maintain social dominance hierarchies.
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