ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



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when other foods are not readily available. However, the presence of seal flesh in 

 stomachs of walruses taken in Bering Strait in spring (Brooks 1954; Fay et al. 

 1977; J. J. Burns and L. F. Lowry, personal communication) does not conform 

 to that explanation, for this is an area of shallow water with an abundant 

 molluscan fauna and little or no restrictive ice conditions. Furthermore, in three 

 of five instances known to me, invertebrate prey were found in the stomachs 

 with the seal flesh. Nine of 11 seal-eating walruses identified to sex have been 

 adult males (Chapskii 1936; Mansfield 1958a; Rausch 1970; Fay et al. 1977; 

 L. F. Lowry, personal communication), which suggests that this carnivory is 

 basically a masculine habit. 



Rate of Intake of Food per Day 



Vibe (1950:35) reported that walruses in the Thule District of northwestern 

 Greenland in summer tend to come inshore to feed for 4 to 6 h during each flood 

 tide, at depths ranging from 15 to 25 m. After filling their stomachs, they 

 withdraw "at ebb, either to continue foraging at greater depths, or to go to sleep 

 on a drifting ice floe." This finding suggests that the animals tend to fill their 

 stomach twice per day and to spend a total of about 8 to 12 h in doing so. 



The full stomach of an adult male, according to Brooks (1954), weighed 

 49.4 kg. Based on the findings of Fay et al. (1977), about 5.4 kg of that would 

 have been the weight of the stomach itself, and about 0.5 kg would have been 

 the weight of inorganic sediments; hence the total weight of the food in the full 

 stomach probably was about 43.5 kg. That this was an exceptionally large 

 amount is suggested by the findings of Krylov (1971), who recorded the largest 

 amount in any one stomach as 5 kg, and Fay et al. (1977), who found the largest 

 amount in 107 stomachs to be 25 kg. Assuming that these maxima (43.5 and 

 25 kg) are representative of recently filled stomachs, and that, as Vibe (1950) has 

 indicated, walruses tend to fill their stomach twice per day, the total daily intake 

 of food may be between about 50 and 85 kg. That this is a reasonably close esti- 

 mate of the daily rate of consumption is indicated by the feeding rates of captive 

 walruses reported by Reventlow (1951), Bridges (1953), Hagenbeck (1963), 

 Brown and Asper (1966), and G. C. Ray (personal communication). 



Nine young walruses that were reared in captivity on diets made up mainly of 

 oily fishes (herring, Clupea harengus; bonito, Sarda chiliensis) and clam meats 

 (mainly Mya arenaria), consumed these foods in amounts ranging from 4.2 to 

 6.2% of their total body weight per day (Table 24). At that rate, the average 

 free-living adult female (at TBW = 820 kg) would consume between 34 and 

 51 kg of food per day, and the average adult male (at TBW = 1,200 kg) 

 between 50 and 74 kg per day. These amounts are about equivalent to filling the 

 stomach twice per day. They may be somewhat lower than the actual rates, for 

 the gross energy content per unit weight of the foods eaten by the captive animals 

 was higher than that of most of the foods eaten by free-living walruses. Although 

 the free-living walruses reside in a colder environment, they probably do not 

 expend more energy in thermoregulation than the captives, but they do expend 

 more in acquiring their food. 



The approximate gross energy values of the daily food intakes of the captive 

 walruses, on the basis of caloric values given by Spector (1956), were about 63 to 

 121 kcal/kg TBW per day. In terms of "metabolic body size" ( = TBW kg3/4)^ 



