ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



141 



year, (6) they usually are fully weaned at 2 years of age, but (7) a few may 

 continue to suckle for another year if not supplanted by a younger, more 

 dependent calf. 



Composition of Walrus Milk 



I collected four samples of milk from walruses taken in May 1958. The first 

 three samples were obtained by severing the lactiferous duct beneath the skin 

 and catching the milk in a sterile container. The fourth sample was taken from 

 the stomach of a calf (about 1 week old) that had been suckling immediately 

 before it was killed. I collected one comparative sample from the stomach of a 

 2-to 3-week-old bearded seal {Erignathm barbatus); three samples from adult 

 northern fur seals were supplied by R. S. Peterson and E. T. Lyons from females 

 that were 1 h prepartum, 36 h postpartum, and about 10 days postpartum 

 (Table 20, Samples I, II, and III, respectively). 



A pinch of powdered bichloride of mercury was added to each sample at the 

 time of collection and thoroughly mixed with it to inhibit fermentation of any 

 sugars present. After collection, the samples were cooled to 0 ± 2°C and stored 

 at that temperature for about 2 weeks. The samples were analyzed by H. F. 

 Meyers and M. Arnow of the Sanitation Chemistry Laboratory, Arctic Health 

 Research Center, Anchorage, Alaska. 



The analytical results (Table 20) indicate that in gross composition the milk of 

 walruses resembles that of other pinnipeds in having very high fat and protein 

 contents, low water content, and very low or no reducing sugars (cf. Sivertsen 



Table 20. Gross composition of walrus milk, with comparative analyses of 







milk from 



other pinnipeds. 









Volume 

 (mL) 





Composition (% by 



weight)** 





Sample 



Water 



Fat 



Protein 



Sugar 



Ash 



Walrus 

 I 



II 



III 



IV 



10 

 25 

 30 

 50 



67.6 

 54.0 

 61.5 

 56.5 



13.8 

 31.6 

 26.9 

 32.0 



11.0 

 7.3 

 5.0 



< 0.025b 



< 0.025b 



0.63 

 0.47 

 0.75 

 0.55 



Bearded seal 

 I 



50 



46.4 



49.5 



6.8 



0.05 



0.60 



Fur seal 

 I 



II 

 III 



30 

 30 

 30 



28.1 

 33.1 

 36.6 



59.1 

 54.1 

 49.5 



15.6 

 17.5 

 13.5 



0.02 



0.016 



0.022 



0.36 

 0.41 

 0.60 



^Analyses: water, ash, fat by methods adopted by Association of Official Agricultural 

 Chemists (Horowitz 1955); protein (nitrogen) by modified AO AC methods, using Hengar 

 selenized granules instead of mercury and collecting distillate in boric acid for direct titra- 

 tion; sugar (reducing substances) by ether extraction of fat, followed by protein precipita- 

 toin by Folin-Wu method (Hawk et al. 1947:493) and Benedict's method applied to fil- 

 trate. Composition data are means of replicate analyses (two each), except for Wal- 

 ruses I and II. 



bNo sugars detected to the 0.025% level; not analyzed for smaller amounts. 



