Age Determination and Growth 
Fay (1955) summarizes present knowledge on age determination of 
walruses. In general, the methods depend on polymodal distribution of 
measurements, of which the tusk measurements separated by sexes are best. 
The age data presented in the following sections are based almost en- 
tirely on Fay's presumed age - tusk length relations. There are two other 
methods suitable for use on bull walruses. The first of these is a crude 
indication of age based on baculum size. The other, which Fay believes is 
very satisfactory, depends on cementum rings in the molariform teeth. He 
finds the formation of 2 rings each year in bulls up to 4 years of age and 
a single ring beyond this age. This same method, but with different in- 
terpretation, was described earlier by Brooks (1954). There is some 
question still as to appropriate interpretation of cementum rings which 
cannot be resolved completely until such time as known age walruses are 
available. 
The principal difficulty in using Fay's age - tusk length 
relationships, especially for females, is that a fairly high percentage 
of measurements exceed those which he lists in his table. He finds a 
maximum tusk length from the gum line along the anterior curve of the 
tusk to the tip of 18-3/8 inches at ages 28 and 29 for females. Quite a 
number of tusks from subsequent samples exceed 20 inches in length. Ac- 
cording to Fay, tusk growth no longer keeps up with wear after age 28. 
Variability of this sort is certainly to be expected, since tusk length 
is a measure of two factors--one of growth and the other of wear. Even 
though growth may be fairly constant between individuals, wear could be 
expected to vary considerably, depending upon bottom conditions with 
which the individual animals are in contact in their process of feeding. 
Regardless of such inconsistencies, the method seems usable as an 
indicator of relative age. 
Population Dynamics 
Reproduction 
Fay (1955) reports that some males are sexually mature at the 
age of 5 years and that most males are sexually mature between 6 and 8 
years of age. Most females, according to him, reach sexual maturity at 
age four. 
The main breeding season extends from March through May, and 
copulation takes place during northward migrations. Copulation is prob- 
ably almost always on the ice although one or two observations indicate 
its possible occurrence in the water. Breeding apparently is promis- 
cuous, tending toward polygamy. The gestation period is approximately 
13 months and births take place from April to June with the peak in mid- 
May. Birth is on the ice and is very rapid, lasting only a few minutes. 
Multiple births are rare, but Nikulin (1954) gives several records of 
twin foetuses. Females apparently breed in alternate years at most, and 
