Abstract

Since the mid-1980s, the sea otter population in the southwestern population stock in Alaska has declined 56-68%. The loss of sea otters in the nearshore marine ecosystem may precipitate changes in distribution and abundance of kelp and forage fish in the nearshore system. Decreased kelp and increased sea urchin numbers in the nearshore ecosystem in the Aleutian archipelago are evident as a result of precipitous population declines of sea otters. During the 1990s, the sea otter population in the Aleutian archipelago declined at a rate of 17.5% yr^-1 and overall, counts decreased by 70% throughout the archipelago by 2000; islands in the central and western archipelago have declined an additional 62% since 2000 and we estimate as few as 3,296 sea otters remain. In 2000 and 2001, surveys of the Alaska Peninsula indicate abundance estimates of sea otters declined by 27-49% along the northern Peninsula and 93-94% along the southern Peninsula since 1986. Counts along the southern Alaska Peninsula coast declined by 38% in the study area but increased by 16% eastward of the study since 1989. In all study areas, sea otters were concentrated in bays and lagoons of the Peninsula, whereas historically, large rafts were distributed offshore as far as 50km. In the Kodiak archipelago, sea otter abundance estimates have declined 56% at an estimated rate of 6.7% yr^-1 since 1989. Since 1989, there has been no population range expansion documented and overall density has decreased in the nearshore habitat in the Kodiak archipelago. Sea otter population declines are similar among survey areas in the following ways: 1) severity, 2) the decline occurred within similar time periods, and 3) severe declines of pinniped populations have occurred in the same general region. Because of the significance of this region to the species, the U. S. Fish and Wildlife Service proposed listing of the stock as threatened under the Endangered Species Act. The cause(s) of the population decline have been hypothesized to be predation by killer whales for the Aleutians, however, data on survival, health, condition, habitat and behavior for other regions is lacking. The population declines in southwest Alaska are one of the most significant conservation issues in our time for the northern sea otters.

References

1.  Burn DM, AM Doroff. 2005. Decline in Sea Otter (Enhydra lutris kenyoni): Populations Along the Alaska Peninsula, 1986-2001. Fishery Bulletin 103:270-279.

2.  Burn DM, AM Doroff, M T Tinker. 2003. Carrying Capacity and Pre-decline Abundance of Sea Otters (Enhydra lutris kenyoni) in the Aleutian Islands. Northwest Naturalist 84:145-148

3.  Doroff AM, JA Estes, MT Tinker, D M. Burn, JA Evans. 2003. Sea Otter Population Declines in the Aleutian Archipelago. Journal of Mammalogy 84:55-64.

4.  Doroff AM, DM Burn, RA Stovall, VA Gill. In prep. Unexpected population declines of sea otters in the Kodiak Archipelago, Alaska.

5.  Estes JA, MT Tinker, AM Doroff, DM Burn. 2005. Continuing sea otter population declines in the Aleutian archipelago. Marine Mammal Science. 21:169-172.