154 



Fishery Bulletin 101(1) 



50 



40 



30 



20 



g' 10 



0- 



2 50 



40- 



30 



20 



10 



Male Pup 



Female Pup 



Immature Male (age 3) 



Immature Female (age 3) 



Mature Male (age 10) 



Mature Female (age 10) 



Mean 

 ±SD 



Pregnant Female (age 10) 



-1 — 1 — I — I — I — 1 — I — I — I — I — I — — I — I — I — I — I — I — I — 1 — I — I — I— 



Jun Sep Dec Mar Jun Sep Dec Mar Jun Sep Dec Mar Jun Sep Dec Mar 



Date 



Figure 3 



Food bioniass requirements for individual Steller sea lions in southeast Alaska by day of the year. Pup food 

 requirements represent the amount of food a female would require to support an entirely dependent pup. 

 SDs were obtained by using Monte Carlo simulations (1000 runs). We assumed the date of birth was 15 

 June. Note that these are plots of food requirements, not food consumption. For example, mature males do 

 not consume food during the breeding season fast (late May-early July). 



lation consumed the most prey biomass on an annual basis 

 (121,000 |±23,300| t) and the central Aleutian Islands 3 

 population consumed the least (12,500 (±24701 t). The 

 large difference in total consumption primarily reflects 

 the large difference in population size between regions. 

 For southeast Alaska, the only region where diet infor- 

 mation was available for all four seasons, the estimated 

 prey biomass consumed on an annual basis increased 

 from 121,000 (±23,300) t (assuming a summer diet all 

 year) to 140,000 (±27,800) t (when diet changed season- 

 ally) because of higher proportions of low-energy-density 

 prey in the diet (and therefore lower energy density of the 

 diet) in autumn, winter, and spring (Table 2). The CVs of 

 total annual p()[)ulation food biomass consumption were 



19-20'/r. 



Based on summer diets, the predicted average daily 

 food requirement per individual (all ages) ranged from 16 

 (±2.8) kg (.southeast Alaska) to 20 (±3.6) kg (central Aleu- 

 tian Islands Isubarea 31 ) — a 24';? difference ( P"ig. 4 ). The 

 average daily per capita food requirement for southeast 



Alaska increased by 3 kg (to 19 |±3.41 kg) when the diets 

 for all four seasons were considered. In general, per capita 

 food requirements were lowest in regions where Steller 

 sea lions consumed high proportions of high-energy- 

 density prey (forage fish and salmon), as in the eastern 

 Aleutian Islands and central Aleutian Islands (subarea 

 1 ), and were highest in regions where the diet contained 

 larger proportions of low-energy-density prey (gadids and 

 hexagrammids), as in the western Aleutian Islands and 

 central Aleutian Islands (subareas 2 and 3). 



The greatest estimated consumption of a single prey 

 species category in a region in 1998 was 68,600 (±14,400) 

 t of gadids in southeast Alaska (using diet information for 

 all seasons; Fig. 5). Gadids were consumed in a similar 

 amount in the Gulf of Alaska (62,700 (±12,8001 t). Alaska- 

 wide, the top two prey categories in terms of biomass 

 consumption were gadids and hexagrammids (gadids 

 - 179,000 1±36,7001 1, hexagrammids- 104,000 |±20,6001 1 ). 

 The Steller sea lion population in the central Aleutian 

 Islands (subarea 2) (Fig. 1 ) consumed the most hexagram- 



