The polar bear, Ursus maritimus, is the apex marine predator of the Arctic ecosystem. Its survival is intricately linked to the sea ice, which serves as a hunting platform for its preferred prey. While polar bears do eat fish, including cod, their diet is not centered on these species. The vast majority of their nutrition comes from marine mammals, with fish acting only as an occasional, opportunistic food source. This specialization results from the extreme energetic demands of the frigid Arctic environment.
The Primary Diet of Polar Bears
The polar bear’s physiology and hunting behavior evolved almost exclusively to target seals, primarily the ringed and bearded seal. This reliance is driven by the necessity to consume massive quantities of fat. Seal blubber provides the high-energy caloric load required to fuel the bear’s size and build the thick fat reserves necessary for insulation and survival during extended fasting periods.
To prepare for fasting, the spring hunting season is a period of intense feeding, where a bear may consume up to 45 kilograms of blubber in a single sitting. Hunting techniques are specialized for the ice environment, such as “still-hunting,” where the bear waits patiently at a seal’s breathing hole (aglu). Bears also stalk seals basking on the ice surface, using camouflage to approach before launching an explosive attack. The high-fat content ensures that the energy gained far outweighs the energy expended.
Fish and Cod Consumption
Polar bears are capable of eating various fish species, including Arctic cod, salmon, and pollock, but they seldom do so by choice. Fish generally lack the dense blubber layer polar bears require to meet their high caloric needs. Hunting and catching fast-moving fish often results in a negative energy balance, as the few calories gained from lean fish meat do not compensate for the energy used in the hunt.
Fish consumption is typically limited to situations where the prey is easily accessible or already dead, making the energetic cost zero. This includes scavenging on stranded fish, such as Greenland sharks, or catching fish trapped in shallow pools as the tide recedes. In periods of severe seal scarcity, fish species like Arctic char may be consumed, but this is an act of desperation, not a sustainable dietary shift. Fish provide protein but cannot replace the highly efficient fat from seal blubber necessary for long-term survival.
Opportunistic and Scavenged Foods
When seals are unavailable, particularly when bears are forced ashore, their diet shifts to whatever is locally available, demonstrating an opportunistic foraging strategy. These supplementary food items help stave off hunger but do not provide the caloric density necessary to sustain the bear over long periods.
Items consumed can include terrestrial sources like small rodents, caribou, waterfowl, and plant matter such as berries and kelp. Bears also readily scavenge marine mammal carcasses that wash ashore, such as the remains of beluga or bowhead whales. The blubber and meat from these carcasses represent a substantial, though unpredictable, source of fat. Other foods include bird eggs and hatchlings consumed when encountering seabird colonies.