Fishery Bulletin 104(1) 



1982). The average seasonal energy density of each prey 

 species was calculated by summing all values of energy 

 dens.ty and dividing by the number of months in the 

 study period. Previously published proximate composition 

 values for surf smelt {Hypomesus pretious) and energy 

 density data for euphausiids (Thysanoessa spp.) were 

 used (Davis et al., 1997; Payne et al., 1999). 



Seasonal prey consumption for the population was es- 

 timated by multiplying 1 by estimates of abundance (A^ ) 

 and the total number of days in the humpback whale 

 feeding season. Consumption estimates were calculated 

 for both the upper and lower 95% confidence limits on 

 the abundance estimates to show a possible range of 

 consumption. The length of the feeding season was pre- 

 sumed to be 152 days (Perez and McAllister, 1993). 



Results 



Analysis of sightings showed that humpback whales 

 were not uniformly distributed within the study area 

 (Table 1). Occurrence of humpback whales within sub- 

 areas was variable, indicating within-season shifts of 

 habitat use. Peak humpback whale sightings occurred 

 in subarea 2 in July of both years. No humpback whales 

 were sighted in the nearshore area after the month of 

 July in either year. 



Only two prey items were identified in the 27 stom- 

 achs that contained appreciable quantities of prey of 

 39 stomachs analyzed by Thompson (1940). Surf smelt 

 were found in 21 of 27 (78%) stomachs and euphausiids 

 were found in 6 of 27 (22%) stomachs (Table 2). These 

 percentages represent diet A. Energy densities of these 

 two species combined to give a total energy density of 

 1.31 kcal/gram (Table 3). 



The fish species in areas used by humpback whales 

 in 2001 and 2002, as shown by mid-water trawl sur- 

 veys, were pollock (36.96%), capelin (28.89%), eula- 



chon (7.60%), Pacific sandlance (4.44%), Pacific sandfish 

 (0.08%), and Pacific herring (0.03%) (Table 2). These 

 percentages represent diet B. Calculated energy densi- 

 ties of prey species ranged from a high (eulachon) of 

 2.52 kcal/gram to a low of 1.12 kcal/gram (juvenile 

 pollock). The total energy density for diet B was 1.19 

 kcal/gram (Table 3). 



Based on energetic content of the above diets, the 

 model indicated that each humpback whale in the study 

 area would consume 338 kg/day on diet A and 370 kg/ 

 day on diet B. Using a prewhaling estimate of 343 (95% 

 CI=331-376) animals in the study area, we determined 

 that humpback whales feeding on diet A prior to 1927 

 would have removed an estimated 1.76x10" kg of prey 

 annually (95% CI= 1.70x10" to 1.93x10"), including 

 nearly 3.87 xlO^ (3.74x10^ to 4.24x106) kg of euphausi- 

 ids and approximately 1.37x10" (1.32x10" to 1.50x10") 

 kg of surf smelt (Table 4). If diet B accurately reflects 

 prey selection by the estimated 157 (95% 01 = 114-241) 



