Digestibility of ringed seals by the polar bear

The digestive efficiency of polar bears (Ursus maritimus) feeding on their principal prey, the ringed seal (Phoca hispida) is high. Apparent digestibilities of 83.7 ± 10.3% for dietary protein, 97.3 ± 2.1% for dietary fat, and an assimilation of dietary energy of 91.7 ± 5.8% were found for the five diets. Presence of hair and bone in the diet significantly reduced the apparent digestibility of protein N. Gastrointestinal transit times were affected principally by the fat (energy) content of the diet and varied between 12.3 ± 1.9 to 38.0 ± 8.0 h. The results explain the apparent preference for seal blubber by polar bears in the arctic as well as demonstrate that any seal > 1 month of age would satisfy the bear's daily energy requirements. The limiting factors in energy intake at a given feeding are the stomach capacity of the bear and the relative proportion of blubber and meat ingested.