Keystone predator; often limits prey populations; predation on herbivores determines structure of off-shore kelp communities (e.g., Estes et al. 1989).
Males defend contiguous territories from which they exclude other males (Riedman and Estes 1990).
Males may move up to 30-60 miles along coast, females generally stay within area 5-10 miles long. Daily movements generally encompass a few kilometers (Riedman and Estes 1990). Ralls et al. (1996) found that otters in California usually were within 1-2 km of their location on the previous day but often stayed in one place for an extended period then suddenly moved a much greater distance; the area used by individual otters during a single 24-hour period was 7-1166 ha.
Undisturbed populations can increase at about 17-20%/year, although the central California population never has increased at more than 5-7%/year (Riedman and Estes 1990).