Estimated prey requirements of wild killer whales, based on two plausible values for calorie content of a typical, 4-year-old Chinook salmon.

Salmon of length 81 cm and mass 8.5 kg, the preferred size of Chinook prey of the resident killer whales [17]. Energy requirements predicted for southern resident killer whale (SRKW) population assume that activity levels are equal in captivity and in the wild. The “calorie-rich” scenario assumes an average energy density of 2,200 kcal/kg [44, p. 57)]; therefore each Chinook was estimated to represent 18,700 kcal. The “lean Chinook” scenario uses the mean of 5 Chinook of unknown size, collected in the Gulf of Alaska (mean = 5.35 kJ/g = 10,869 kcal/8.5 kg fish; [45]). Note that the row in bold type represents the most plausible estimate, based on observed body sizes from whaling records from the northeastern Pacific. The SRKW population in 2009 consisted of 87 individuals of the following age-sex classes (Center for Whale Research): females with calves (10); adult males (23); juveniles (15); calves (10); and adult females without calves (29).