270 



Abstract— During the 1990s, sea otter 

 i En hydra lutris) counts in the Aleu- 

 tian archipelago decreased by 70% 

 throughout the archipelago between 

 1992 and 2000. Recent aerial surveys 

 in the Aleutians did not identify the 

 eastward extent of the decline; there- 

 fore we conducted an aerial survey 

 along the Alaska Peninsula for com- 

 parison with baseline information. 

 Since 1986, abundance estimates 

 in offshore habitat have declined 

 by 27-49% and 93-94% in north- 

 ern and southern Alaska Peninsula 

 study areas, respectively. During this 

 same time period, sea otter density 

 has declined by 63% along the island 

 coastlines within the south Alaska 

 Peninsula study area. Between 1989 

 and 2001, sea otter density along the 

 southern coastline of the Alaska Pen- 

 insula declined by 35% to the west of 

 Castle Cape but density increased by 

 4% to the east, which may indicate an 

 eastward extent of the decline. In all 

 study areas, sea otters were primar- 

 ily concentrated in bays and lagoon, 

 whereas historically, large rafts of 

 otters had been distributed offshore. 

 The population declines observed 

 along the Alaska Peninsula occurred 

 at roughly the same time as declines 

 in the Aleutian islands to the east 

 and the Kodiak archipelago to the 

 west. Since the mid-1980s, the sea 

 otter population throughout south- 

 west Alaska has declined overall by 

 an estimated 56-68%, and the decline 

 may be one of the most significant 

 sea otter conservation issues in our 

 time. 



Decline in sea otter (Enhydra lutris) populations 

 along the Alaska Peninsula, 1986-2001 



Douglas M. Burn 



Angela M. Doroff 



Marine Mammals Management Office 



U.S. Fish and Wildlife Service 



10H East Tudor Road 



Anchorage, Alaska 99503 



E-mail address (for D M Burn): douglas_burnifi'fws gov 



Manuscript submitted 2 September 

 2003 to the Scientific Editor's Office. 



Manuscript approved for publication 

 30 August 2004 by the Scientific Editor. 



Fish. Bull. 103:270-279 (2005). 



During the 1990s, the sea otter 

 (Enhydra lutris) population in the 

 Aleutian archipelago declined at a 

 rate of 17.5%/yr and, overall, counts 

 decreased by 70% throughout the 

 archipelago between 1992 and 2000 

 (Doroff et al., 2003). By modeling 

 population trends back to the mid- 

 1980s, Burn et al. (2003) estimated 

 the population in the Aleutian Island 

 chain decreased by 65,000 sea otters 

 and was at about 10% of its carry- 

 ing capacity in 2000. The 2000 aerial 

 survey of Doroff et al. (2003) did not 

 identify an eastward extent of the 

 population decline however; therefore 

 additional sea otter surveys along the 

 Alaska Peninsula were needed. 



Historic information on population 

 status and trends is sparse for sea 

 otters along the Alaska Peninsula. 

 Sea otters were exploited to near ex- 

 tinction in the commercial fur trades 

 (1742-1911) and were removed from 

 large portions of their historic range 

 worldwide (Kenyon, 1969; Lensink, 

 1962). At the time of their protec- 

 tion in 1911 by an international fur 

 seal treaty, there were 13 remnant 

 populations remaining worldwide, 11 

 of which persisted and grew to re- 

 colonize much of the former range of 

 this species (Kenyon, 1969). Studies 

 of both remnant native and translo- 

 cated sea otter populations have in- 

 dicated a pattern of colonization with 

 high population growth rates up to 

 20% per year, and an expansion into 

 adjacent, unoccupied habitat (Estes, 

 1990). 



One remnant population survived 

 on the north side of the Alaska Pen- 



insula near Unimak Island (Kenyon, 

 1969; Schneider, 1976). Sea otter 

 habitat in this area is unique in that 

 shallow water (less than 100 m) ex- 

 tends up to 50 km offshore, covering 

 more than 10,000 km of open water. 

 The remnant population in this ar- 

 ea likely numbered fewer than 100 

 sea otters in 1911 (Kenyon, 1969). 

 This population grew steadily and 

 expanded its range to the northeast 

 along the Peninsula until 1970, when 

 extreme sea ice conditions temporar- 

 ily reduced the range and likely the 

 size of the population (Schneider and 

 Faro, 1975). By 1976, most of the sea 

 otters in this area were concentrated 

 between Cape Mordvinof and Cape 

 Leontovich (Schneider, 1976). 



In addition to the remnant popu- 

 lation on the north side of Unimak 

 Island, there were also two remnant 

 populations of sea otters located to 

 the south of the Alaska Peninsula 

 in the Sandman Reefs and the outer 

 Shumagin Islands (Kenyon, 1969). 

 Sea otter habitat along the southern 

 Alaska Peninsula differs from the 

 northern side and comprises primar- 

 ily rocky, mixed substrate, and ex- 

 tensive offshore reefs (Brueggeman et 

 al. 1 ). In the Sandman Reefs a small 

 number of sea otters were sighted in 



1 Brueggeman, J. J., G. A. Green, R. A. 

 Grotefendt, and D. G. Chapman. 

 1988. Aerial surveys of sea otters in 

 the northwestern Gulf of Alaska and 

 the southeastern Bering Sea. Minerals 

 Management Service and NOAA final 

 report, 87 p. Minerals Management 

 Service, Anchorage, AK. [Contract no. 

 85-ABCV-00093.] 



