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Fishery Bulletin 103(2) 



merits were made in 1990, 1991, and 1994 on Marmot 

 Island (58°12'N, 151°50'W), in 1993 on Chirikof Island 

 (55°10'N, 155°8'W) and in 1995 on Fish Island (59°53'N, 

 147°20'W). On the Aleutian Islands of Seguam (52°30'N, 

 172°30'W) and Yunaska (52°45'N, 170°45"W), pups were 

 studied in 1997. Data from Seguam and Yunaska Islands 

 were combined because the islands are geographically 

 close and can be considered part of one rookery complex. 

 Rookeries in the Gulf of Alaska and the Aleutian Islands 

 are in the area of declining population, although the 

 rookery on Fish Island has not shown as precipitous a 

 decline. Samples could not be obtained from all rooker- 

 ies in all years because of logistical constraints and the 

 need to minimize disturbance to rookeries. However, 

 concurrent data were obtained from the declining and 

 stable populations in 1993, 1994, and 1997. 



Only pups that had an attached umbilical cord or an 

 unhealed umbilicus were selected for study. The fresh- 

 ness of the umbilical cord was used as a rough estimate 

 of age between 1 and 5 days (Davis and Brandon 3 ). 



3 Davis, R. W, and A. A. Brandon. Unpubl. data. I Data are 

 on file at Texas A&M University, 5007 Avenue U, Galveston, 

 Texas 77551.1 



Choosing only pups with fresh umbilical cords mini- 

 mized the age bias (Trites, 1993) that occurs when pups 

 are captured at different times and rookeries (Table 1). 



Although pups were not selected by sex, sex was 

 noted and used as a factor in analyses. Body mass 

 (BM), standard length (SL), axillary girth (AG) (Am. 

 Soc. Mammalogists, 1967) and body composition were 

 measured for each pup. BM was measured to the near- 

 est kilogram with a mechanical spring scale (Chatillon 

 160, Ametek, FL) on Marmot Island in 1990 and 1991 

 and on Lowrie Island in 1993. Body mass of pups at all 

 other sites and years was measured to the nearest tenth 

 of a kilogram by using an electronic scale (Rice Lake 

 Weighing Systems, Rice Lake, WI; Ohaus I-20W, Ohaus, 

 Pine Brook, NJ). Standard length was measured as a 

 straight line from tip-of-nose to tip-of-tail, ventral sur- 

 face down. Pups were restrained by hand and marked 

 for later identification with hair bleach (Lady Clairol 

 Maxi Blond, Clairol, Inc.) and with flipper tags attached 

 in the axillary area of the fore-flippers. 



Body composition was measured by using the labeled 

 water method (Nagy 1975; Nagy and Costa, 1980; Cos- 

 ta, 1987; Bowen and Iverson, 1998). In this study, water 

 labeled with a stable isotope of hydrogen (deuterium) 



