Age determination 
The ages of all seals tagged as pups and later recovered are 
known directly. The ages of untagged animals are determined from tooth- 
ridge counts. The teeth of a seal show a series of annular ridges on the 
dentine, or ivory, of the root (fig. 2). These are a result of changes 
in the physiological condition of the seal during the year. Ridges are 
formed during the winter, and depressions during the summer (Scheffer, 1950a). 
They usually provide reliable readings for ages both of males and of females, 
up to 10 or 12 years. Other features, such as length of tooth, attrition 
of the crown, and closure of the pulp canal, provide additional evidence 
of age. Teeth recovered from a large series of tagged seals whose ages 
are accurately known have provided standards for age determination. Since 
1949 it has been the practice to save the right upper canine from every 
seal skull which is expected to have subsequent research value. 
A random sample of 20 teeth was taken daily from the killing 
fields in 1950, 1951, and 1952 (with some exceptions during the first 
few days of the season). Each tooth was read for age. Studies were then 
made of the age composition of the entire kill as well as the age variation 
during different periods in the season, among the different hauling 
grounds, and in different years. 


Figure 2. Fur-seal tooth. Right upper canine of a 
known-age (tagged) 9-year female seal showlng annular growth- 
ridges on the root: actual length of tooth 35 mn. (VBS 2898A) 
-5= 
