246 



Abstract— The growth rate of Steller 

 sea lion (Eumetopiasjubatus) pups was 

 studied in southeast Alaska, the Gulf 

 of Alaska, and the Aleutian Islands 

 during the first six weeks after birth. 

 The Steller sea lion population is cur- 

 rently stable in southeast Alaska but 

 is declining in the Aleutian Islands 

 and parts of the Gulf of Alaska. Male 

 pups (22.6 kg [±2.21 SD]) were sig- 

 nificantly heavier than female pups 

 (19.6 kg [±1.80 SD]) at 1-5 days of 

 age, but there were no significant dif- 

 ferences among rookeries. Male and 

 female pups grew (in mass, standard 

 length, and axillary girth) at the same 

 rate. Body mass and standard length 

 increased at a faster rate for pups in 

 the Aleutian Islands and the western 

 Gulf of Alaska (0.45-0.48 kg/day and 

 0.47-0.53 cm/day, respectively) than 

 in southeast Alaska (0.23 kg/day and 

 0.20 cm/day). Additionally, axillary 

 girth increased at a faster rate for 

 pups in the Aleutian Islands (0.59 cm/ 

 day) than for pups in southeast Alaska 

 v(0.25 cm/day). Our results indicate a 

 greater maternal investment in male 

 pups during gestation, but not during 

 early lactation. Although differences 

 in pup growth rate occurred among 

 rookeries, there was no evidence that 

 female sea lions and their pups were 

 nutritionally stressed in the area of 

 population decline. 



Neonatal growth of Steller sea lion 

 (Eumetopias jubatus) pups in Alaska 



Elisif A. A. Brandon 



Department of Marine Biology 

 Texas A&M University at Galveston 

 5007 Avenue U 

 Galveston, Texas 77551 

 Present address: 97A Lowell Ave 



Newton, Massachusetts 02460 



Donald G. Calkins 



Alaska SeaLife Center 

 P.O. Box 1329 

 Seward. Alaska 99664 



Thomas R. Loughlin 



National Marine Mammal Laboratory 

 Alaska Fisheries Science Center, NMFS 

 7600 Sand Point Way, NE 

 Seattle, Washington 98115 



Randall W. Davis 



Department of Marine Biology 



Texas A&M University at Galveston 



5007 Avenue U 



Galveston, Texas 77551 



E-mail address (for R. W Davis, contact author): davisngitamug edu 



Manuscript submitted 26 April 2004 

 to the Scientific Editor's Office. 



Manuscript approved for publication 



2 December 2004 by the Scientific Editor. 



Fish. Bull. 103:246-257 (2005). 



Sea lion (order Carnivora, family 

 Otariidae) pups depend entirely on 

 milk for neonatal growth (Bonner, 

 1984). Studies of sea lions and fur 

 seals have shown that if a pup does 

 not obtain enough milk from its 

 mother, it will exhibit poor body condi- 

 tion (i.e., reduced lean mass and total 

 lipid mass for a given age or standard 

 length) and a reduced growth rate 

 (Trillmich and Limberger. 1985; Ono 

 et al., 1987). Poor body condition and 

 reduced growth rate, in turn, may 

 have lifelong consequences because 

 neonatal growth is an important 

 factor in determining adult size and 

 survival (Bryden, 1968; Innes et al., 

 1981; Calambokidis and Gentry, 1985; 

 Albon et al., 1992; Baker and Fowler, 

 1992; Gaillard et al., 1997; Boltnev et 

 al., 1998; Tveraa et al„ 1998; Burns, 

 1999). Because of their large size, 

 aggressive behavior, sensitivity to 

 disturbance, and the remote location 



of their rookeries, less is known about 

 the early growth of Steller sea lions 

 (SSL) than of most other pinniped 

 (seals, sea lions, and walrus) species. 

 Higgins et al. (1988) measured body 

 mass of SSL pups on Ano Nuevo Island 

 in California but only reweighed five 

 pups to measure growth rates. Mer- 

 rick et al. (1995) weighed SSL pups 

 at a number of locations throughout 

 the Gulf of Alaska and the Aleutian 

 Islands but did not reweigh them to 

 assess individual growth rates. 



Genetic studies show that there are 

 distinct eastern and western popula- 

 tions of SSL (Bickham et al., 1996, 

 1998) (Fig. 1). The eastern population 

 comprises animals in California, Ore- 

 gon, British Columbia, and southeast 

 Alaska. The western population com- 

 prises animals in the Gulf of Alaska, 

 the Aleutian Islands, the Bering Sea, 

 the Commander Islands, Kamchatka, 

 and the Kuril Islands. A severe popu- 



