Study of mortality in sea otter (Enhydra lutris) on the Commander Islands in population monitoring

Carcasses of sea otters (1871 on Bering Island and 179 on Mednyi Island) were collected from January 1984 to July 1991. The number, spatial distribution, age and sex composition of the carcasses, their seasonal and annual differences were analyzed. The maximum mortality occurred in the winter-spring period. The abundance and composition of the beached carcasses depend on the concentration of living animals, sea currents, and general wind directions. Within a year, the number of the findings correlated positively with weather conditions. Meanwhile, from year to year weather conditions differed weakly and affected insignificantly the mortality of the animals. The information from the sea otter carcasses collected for many years allows one to characterize the annual demographic situation and determine trends of developing populations. The history of restoring the sea otter population on the Commander Islands is briefly reviewed. The developmental phases of the subpopulation on Bering Island are characterized by increasing the number predominantly at the expense of immigrants (mainly males) from Mednyi Island and by the predominance of reproduction over immigration. The stabilization of the age and sex structure of both parts population is possible in the nearest future. The changes in the developmental phases were accompanied by an increase in mortality, especially among males.