MERRICK ET AL.: DECLINE OF NORTHERN SEA LION 



RESULTS 



1984-86 Survey Findings 



The 1984 survey of the eastern Aleutian Islands 

 resulted in a count of 9,833 adult and juvenile north- 

 ern sea lions on 16 sites (Table 1). The six rookery 

 islands surveyed included 7,934 animals (Table 2), 

 91% of the total count. One rookery, Adugak Island, 

 and several haul-out sites were not surveyed owing 

 to inclement weather. 



A total of 10,802 adult and juvenile northern sea 

 lions were seen in the 1985 survey of the eastern 

 Aleutian Islands (Table 1), which was not significant- 

 ly different from the 9,833 animals counted there 

 in 1984 (P > 0.05). A total of 67,617 animals were 

 counted at 105 sites in the entire study region. Most 

 (60%) of the animals were associated with the 27 

 rookeries surveyed; the largest rookeries were in 

 the central Gulf of Alaska, notably at Marmot 

 Island, and in the Central Aleutian Islands. The 

 rookery on Semisopochnoi Island was not surveyed; 

 eight previously identified haul-out sites were un- 

 occupied. 



Observers in the 1985 shipboard survey counted 

 4,950 pups at six rookeries in the eastern Aleutian 

 Islands and 9,170 pups at nine rookeries in the cen- 

 tral Aleutian Islands (Table 3). In the 1984 and 1986 

 pup surveys of six rookeries in the Gulf of Alaska 



Table 1 .—Counts and percent declines of adult and juvenile north- 

 ern sea lions at all sites in spring and summer 1956-85 in the 

 Aleutian Islands and Gulf of Alaska. 



'Reference: 1— Mathisen and Lopp (1963); 2— Kenyon and Rice (1961); 

 3— Kenyon (text fn. 3); 4— Braham et al. (1980); 5— Calkins and Pitcher (text 

 fn. 5); 6— Fiscus et al. (1981); 7— this study. 



^Significant difference (P < 05) from 1985 using W/ilcoxon signed rank test. 



^Declines calculated from earliest survey date 



(Table 3) 16,278 (excluding Clubbing Rocks and 

 Pinnacle) and 12,025 pups were counted, respec- 

 tively. 



Trends in Regional Numbers 



Comparison of the 1984-85 aerial surveys with 

 historical data (Table 1) shows that significant (P 

 < 0.05) declines have occurred in northern sea lion 

 numbers in the western Gulf of Alaska ( - 73%), and 

 eastern Aleutian Islands ( - 79%). The central Gulf 

 of Alaska (-31%) and central Aleutian Island popu- 

 lations may have also declined since 1957-59, though 

 the decreases ( - 31% and - 8%, respectively) were 

 not statistically significant (P > 0.05). Note that the 

 central Aleutian Islands numbers increased 34% 

 between 1959 and 1979. This suggests that either 

 the population increased markedly, was supple- 

 mented by immigration from other areas (e.g., the 

 eastern Aleutian Islands), or was an artifact of the 

 1979 survey methodology (i.e., a shipboard survey). 

 Linear regression models (Fig. 2) fitted to these 

 counts indicate that the trends of all areas, other 

 than the central Aleutian Islands, exhibit significant 

 negative slopes (P < 0.05). 



The number of adult breeding animals has de- 

 clined in all areas since 1957 except the central Aleu- 

 tian Islands (Table 2). Numbers at the central Aleu- 

 tian Islands rookeries increased by 88% between 

 1959 and 1985, a significant increase (P < 0.01). As 

 the overall population in the central Aleutian Islands 

 decreased between 1959 and 1985, this may indicate 

 that a larger proportion of the population is now 

 breeding than in the past. Rookery populations in 

 the eastern Aleutian Islands have declined 79% since 

 1957, a significant decline (P < 0.05). A loss of 

 15,000 animals occurred at the Ugamak and Akutan 

 Island rookeries alone between 1968 and 1975. 

 Numbers at rookeries in the western and central 

 Gulf of Alaska decreased 66% and 47%, respective- 

 ly, between 1956-57 and 1985. 



Trends in Regional Pup 

 Production 



Pup counts are available for only a few sites prior 

 to 1984. These data (Table 3) show that the number 

 of northern sea lion pups counted in the central Gulf 

 of Alaska decreased between 1979 and 1986 by 44%, 

 from 18,998 to 10,600. The number of pups has also 

 declined at sites in the western Gulf of Alaska and 

 eastern Aleutian Islands. Pupping decreased 52% 

 at Bogoslof Island between 1968 and 1985, 89% at 

 Walrus Island (in the Pribilof Islands) between 1960 



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