
The entries in the table from age 4 upward have been obtained 
by a crude Gompertz-—Makeham mortality curve within the limitations that 
the cumulative number of bulls should be 15,000 to 16,000. The entries 
from age O to 3 represent broad deductions, supported by the reasonable 
assumption that the greatest mortality is experienced in the first 
year of life when the seal pups encounter the rigors of winter at sea 
in the North Pacific. 
Tooth-ridges, so far as they have been studied, have not 
revealed the maximum length of life. Branded seals 18 and 21 years of 
age have been seen on St. Paul Island breeding grounds (U. S. Bureau of 
Fisheries, 1923, pp. 136-137, 1930, p. 105, 1938, p. 163). Recent 
studies of the longevity of several "hair seals" (Phocidae) have been 
published. Fisher (1952) sectioned the teeth of harp seals (Phoca 
groenlandica) and found that the annual layers could usually be read 
up to the age of 20 years, and in one case to 28 years. Sivertsen 
(1941) reported that a gray seal (Halichoerus us) lived for 17 
years in captivity and a harbor seal (Phoca vitulina for 19 years. 
Matheson (1950) recorded the length of life of several gray seals 
kept in captivity, one 18 years, one 26 years 3 months, and one 4] 
or possibly 42 years. Laws (1953) has been able to read tooth rings 
in the elephant seal (Mirounga leonena) to age 20. Considering all 
the evidence, we conclude that the Alaska fur seal may attain an age 
of 30 years. : | 
The life table (15) for female seals is based on the follow- 
ing assumptions and checkpoints: 
1. 265,000 female pups born; the same number as males. 
2. Mortality rates up to age 3 similar to those for males. 
Thus, at beginning of age 3, the number of females 
(67,533) is postulated to be the same as the number of 
males, except for the few hundred males killed at age 2. 
Mortality rates are assumed to be fairly low and uniform; 
4 percent among young, but sexually mature, cows up to 
age 10. No attempt has been made to estimate the rate 
in older cows. 
3. Pregnancy rates are based upon reproductive tracts 
collected on or along the coast of North America, 1948-52. 
The collections included 101 four-year-old females, 51 
five-year-olds, 425 six- to ten-year~olds, and 317 females 
over 10 years of age. 
4. <A total of 364,216 female seals over 10 years of age has 
been predicated simply to bring the total of bearing 
females (right-hand column) up to 530,000, i.e. equal 
to the estimated number of pups born. The value 364,216 
represents 30 percent of all female seals exclusive of 
pups. 
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