Burn and Doroff: Decline of Enhydra lutns along the Alaska Peninsula 



277 



estimated that observers flying in a Twin Otter aircraft 

 recorded 42% of the sea otters present within the area 

 surveyed. Adjusting the 1986 results by this amount 

 yields a range of 10,086-17,238; therefore the popula- 

 tion may not have changed substantially between 1976 

 and 1986. By 2000 however, it is clear that sea otters 

 had declined within the NAP study area, and although 

 the data history for the SAP study area is even more 

 sparse, there is little doubt that the population in this 

 area has also declined severely since 1986. 



The distribution of sea otters along the north side of 

 the Alaska Peninsula is rather unique. Because of the 

 broad shelf, large rafts of otters have been observed 

 at distances of 50 km or more from shore. The area is 

 also subject to seasonal sea ice that can have a pro- 

 found impact on sea otter distribution, and in extreme 

 ice years, result in significant mortality (Schneider 

 and Faro, 1975). It is unclear if behavior and move- 

 ment patterns in the NAP area are different from other 

 areas in the north Pacific. In the 1960s and 1970s it 

 was thought that sea otters along the northern Alaska 

 Peninsula spent much, if not all, of their life in offshore 

 waters (Kenyon, 1969; Lensink, 1962; Schneider. 1976). 

 Cimberg et al. 2 suggested that sea otters may migrate 

 through False Pass from the Bering Sea to the north 

 Pacific Ocean during the winter months to avoid be- 

 ing trapped by shore-fast sea ice. Of the two study 

 areas along the north side of the Alaska Peninsula, 

 the NAPa study area located farther south and west 

 is more likely to remain ice-free, and therefore may be 

 important for the overall survival of sea otters in this 

 area (Schneider and Faro, 1975). If sea otters remain 

 concentrated throughout the year in Port Moller, which 

 is in the NAPb study area, they may be vulnerable to 

 mortality by extensive sea ice events in the future. 



Information derived from sea ice data with spatial and 

 temporal resolution suitable for evaluating the impacts 

 of extensive sea ice on sea otters is not readily available. 

 Detailed sea ice data for the NAP study area from the 

 National Ice Center is only available for the period from 

 1997 to the present. In March 1999 shore-fast ice was 

 present in both Port Moller and Izembek Lagoon, and 

 nearshore areas were almost totally covered by sea ice. 

 Similar conditions also occurred in January 2000. In 

 both instances, sea otter mortality was reported by resi- 

 dents of Port Heiden, Alaska, located to the northeast 

 of the NAP study area (Esslinger 5 ; Snyder 6 ). Human 

 habitation in the NAP study area is extremely sparse in 

 winter, which may explain why there were no reports of 



4 Evans, T. J., D. M. Burn, and A. R. DeGange. 1997. Dis- 

 tribution and relative abundance of sea otters in the Aleu- 

 tian archipelago. Tech. Rep. MMM 97-5, 29 p. U. S. Fish 

 and Wildl. Serv. Mar. Mamm. Manage. Office 1011 E Tudor 

 Road, Anchorage, AK 99503. 



5 George Esslinger. 1999. Personal commun. U.S. Geologi- 

 cal Survey. Alaska Science Center. 1011 East Tudor Road. 

 Anchorage, AK 99503-6103. 



6 Jonathan Snyder. 2000. Personal commun. U.S. Fish 

 and Wildl. Serv., Mar. Mamm. Manage. Office, 1011 East 

 Tudor Road, Anchorage, AK 99503-6103. 



sea otter mortality in this area. Given the degree of sea 

 ice present, it is possible that the extreme ice conditions 

 in 1999 and 2000 may have resulted in the death of 

 some sea otters within our study area. The geographic 

 pattern of the decline does not exactly fit what would 

 be expected from sea ice however, because the decline 

 occurred in the NAPa study area, which is presumed 

 to be less vulnerable to these events. Although it is 

 possible that extreme sea ice conditions may have been 

 a contributing factor, it was likely not the sole cause of 

 the decline in the NAP study area. 



In our surveys of the NAP study area, sea otter abun- 

 dance declined severely in NAPa but had increased in 

 NAPb. It is unclear to what degree otters may move 

 between these respective study areas. Quarterly surveys 

 in 1986 did not indicate seasonal changes in distribu- 

 tion between the NAPa and NAPb portions of the study 

 area. Monnett et al.' used radio telemetry to study sea 

 otter movements in the NAPa study area from 1986 

 through 1988 and found that study animals did not 

 move between NAPa and NAPb or to the SAP study 

 area as previously hypothesized by Cimberg et al. 2 The 

 average distance between extreme locations was only 

 18.4 km; however, the sample size of sea otters in the 

 Monnett et al." study was small (n=14). The large con- 

 centration of sea otters observed in Port Moller and Nel- 

 son Lagoon in May 2000 may be a seasonal event; large 

 numbers of sea otters are typically observed in that 

 area in May, but disperse by June (Murphy*). Compared 

 to the ecology of other areas, the ecology of sea otters 

 along the north side of the Alaska Peninsula is poorly 

 understood and additional study is warranted. 



In addition to changes in abundance there were also 

 changes in sea otter distribution in the 2000-01 sur- 

 veys. In 1986, sea otters were observed up to 50 km 

 from shore during all surveys. In the 1970s and 1980s, 

 large rafts of up to 1000 sea otters were distributed 

 well offshore (Kenyon, 1969; Schneider, 1976; Bruegge- 

 man et al. 1 ). By 2001 sea otters were, with rare excep- 

 tion, located in bays and lagoons along the Peninsula 

 rather than in the offshore habitat in both the NAP and 

 SAP study areas. Estes et al. (1998) hypothesized that 

 declines in sea otters in the Aleutian islands during the 

 1990s may have been caused by increased predation by 

 killer whales (Orcinus orca). One line of evidence that 

 led to this conclusion was a lower sea otter mortality 

 in the sheltered area of Clam Lagoon than in the ex- 

 posed area of Kuluk Bay on Adak Island. The observed 

 distribution of sea otters within bays and lagoons along 

 the Alaska Peninsula in 2000-01 is not inconsistent 

 with the predation hypothesis of Estes et al. (1998). Al- 

 ternatively, nearshore waters may constitute preferred 



Monnett, C, L. M. Rotterman, D. B. Sniff, and J. Sarvis. 

 1988. Movement patterns of western Alaska Peninsula 

 sea otters. Minerals Management Service. OCSEAP (Off- 

 shore Continental Shelf Engineering Assessment Program I 

 Research Unit 688, 51 p. 



Murphy, B. 2002. Personal commun. Alaska Department 

 of Fish and Game, Division of Commercial Fisheries, 211 

 Mission Road. Kodiak, AK 99615-6399. 



