32 



NORTH AMERICAN FAUNA 74 



In 13 specimens from which I recorded both the curvilinear and the standard 

 length, the standard length was about 93% of the curvilinear length. According 

 to Chapskii's (1936) comparative data from about 50 specimens, the horizontal 

 length is about 89% of the zoological length. 



Most of the data on body length of walruses that are available in the literature 

 are either curvilinear or zoological lengths. However, because American 

 zoologists mainly use standard length for comparison of species, populations, and 

 individuals, that measurement alone is used in this report. When only the 

 curvilinear or zoological length of a specimen was available, I estimated the 

 standard length as being 93% of the given length. 



At birth and for at least 1 month thereafter, male and female walrus calves are 

 about equal in length (Table 3). Many of the males already appear to be 

 somewhat broader in the head and shoulders than most of the females, fore- 

 shadowing their eventual unequal development. In the first 2 months, the calves 

 increase in length by about 10 to 15 cm per month. The males probably tend to 

 grow slightly faster than the females, for that trend is clearly evident in their 

 subsequent development (Fig. 19). In both sexes, growth in standard length is 

 most rapid in the first 4 or 5 years and tends to approach its asymptote at 7 to 9 

 years. In the females, full development in length is reached at about 10 years. In 

 the males, however, a secondary acceleration of growth takes place from about 

 the 9th to the 13th year, and full adult length is not attained until about 15 years. 



The few data available from Pacific walruses of known age that have been 

 reared in captivity (triangular symbols. Fig. 19) indicate that their growth in 

 length corresponded closely to that of free-living walruses. The mean length-age 

 curves in Fig. 19 also correspond approximately to those estimated for Atlantic 

 walruses by Mansfield (1958fl), though they suggest that Pacific walruses are 

 about 4 to 7% longer than their Atlantic counterparts. In both populations, the 

 males tend to be 15 to 20% longer than the females, and the length of the 

 newborn calves is about 35 to 40% of that of the adults. 



Table 3. Comparative standard lengths of male and female Pacific walruses." 



Standard length (cm) 

 Males Females 

 Age class No. Range Mean No. Range Mean 



Full-term fetuses and 



newborn calves 



6 



104- 



-122 



112 



11 



95- 



-123 



113 



Calves 



















1-2 weeks 



14 



106- 



-127 



116 



22 



107- 



-126 



116 



2-4 weeks 



15 



116- 



-135 



127 



12 



121- 



-140 



129 



5-8 weeks 



23 



123- 



-171 



140 



21 



121- 



-153 



135 



Adults: males > 14 



















years, females >9 



















years 



55 



279- 



-356 



320 



47 



230- 



-312 



272 



^Sources: Nikulin (1941), Brooks (1954), Krylov (1962), and lU. Bukhtiarov, J. J. Burns, 

 F. H. Fay, and K. W. Kenyon (unpublished data). 



