CONTINUING SEA OTTER POPULATION DECLINES IN THE ALEUTIAN ARCHIPELAGO

Abstract

Recently published data demonstrated a sea otter population collapse across theAleutian archipelago (Doroff et al. 2003). This assessment, undertaken in responseto earlier reports of precipitous declines at several islands (Estes et al. 1998), wasbased on archipelago-wide aerial surveys conducted in 1965, 1992, and 2000, andskiff surveys of particular islands or small island groups during various years fromthe early 1990s through 2000. To summarize the main findings: (1) aerial countsdeclined by about 70% from 1992 to 2000, (2) populations at those islandsthought by Kenyon (1969) to be at or near carrying capacity in 1965 had declined88% by 2000, (3) most of the overall decline occurred after the late 1980s or early1990s, and (4) sea otters had reached a uniformly low population density (numbersper unit length of shoreline) throughout the Aleutian archipelago by 2000. Doroffet al. (2003) interpreted this latter finding to mean that the factors responsible forthe decline were density-dependent, thus implying that a steady state may havebeen attained between killer whale predation, the purported cause of the decline(Estes et al. 1998), and the reduced availability of sea otters. If that conjecture is