Effects of Sea Ice on Sea Otters (Enhydra lutris)

Abstract

Sea ice advanced beyond its normal limits along the Alaska Peninsula in March 1971 and again in February, March, and April 1972. Observations of the reactions of sea otters inhabiting the area to various ice conditions were made during a series of aerial surveys. In 1971 during extremely cold temperatures the ice advanced rapidly through the sea otter habitat. Sea otters were trapped as the ice formed around them. They were forced to travel across the ice and the adjacent land, searching for open water in which to dive for food. Large numbers died from causes related to malnutrition when they could not maintain access to open water; however, little effect on the range of the population was observed. In 1972, the ice advanced more slowly under warmer temperatures. Most of the sea otters were able to move with the ice edge until they were concentrated near the tip of the Alaska Peninsula and Unimak Island. Although the ice in 1972 was denser and persisted longer than in 1971, relatively little mortality was observed, but the distribution of this population was at least temporarily altered. Observations made during the two years indicate that sea otters are able to tolerate severe ice and weather conditions as long as they are able to dive through leads for food. However, the northeastern expansion of the Bristol Bay population is being limited by the periodic formation of heavy sea ice.