age at maturity of the pacific coast salmon 
7 
The scales in different yearlings captured at the same time and place differ considerably 
in size of scale and in the number of rings which they contain. Precisely similar varia- 
tions are found in the nuclear areas of the adult scales, these being larger in some indi- 
viduals than in others, and containing more numerous rings. Every variety of scale from 
migrating yearlings can be matched in the close-ringed centers of adult scales, both as 
regards actual size and in the number and arrangement of the rings. We can entertain 
no doubt, therefore, that the two have had an identical history. (See pi. ii, fig. 4, with 
center of adult scale enlarged 40 diameters.) 
The peripheral part of the scale seldom offers any difficulty. After life has begun 
in the sea, a regular alternation occurs of bands of widely spaced and of narrowly spaced 
rings, as shown in plate iii, figure 6, the widely spaced rings representing the vigorous 
growth of spring and summer, the narrow rings the retarded growth of fall and winter. 
Finally, at the margin of the scale of the mature sockeye about to enter the Fraser are 
found a few widely spaced rings, indicating that the rapid growth of the summer in 
which maturity is attained early comes to an abrupt conclusion. This is true in the 
sockeye in greater degree than in other species of the genus, and may have its explana- 
tion in the earlier date at which mature sockeye discontinue feeding. All species of 
Pacific salmon (the steelhead is not here considered) cease to feed on entering fresh 
water at maturity, but the sockeye is extreme in this regard. Those bound for the 
Fraser are already fasting when first encountered along the Vancouver Island shore at 
the entrance to the Straits of Fuca, where other species are feeding greedily. The 
sockeyes are then over 100 miles from the mouth of the Fraser and are assuredly at 
that time not under the influence of fresh water. Fishermen are well acquainted with 
the fact that the sockeye, unlike the king salmon and the coho, are not to be taken by 
trolling, even when first they strike the coast. 
With these facts in mind, we turn to plate ii, figures 3 and 4, which represent a 
scale typical of a majority of the sockeyes of the Fraser River run. The nuclear area 
of finely crowded rings contains no record of the first winter after the eggs are laid, but 
represents the first summer and second winter which were spent in the lake. The broad 
band of widely spaced rings surrounding the nuclear area was formed in the sea and 
represents the second summer, thus completing the second year of the cycle. Then 
follow a narrow winter band of closely spaced rings and a second distinct summer band, 
constituting the third year of the cycle, and another winter band and the short marginal 
summer band of the fourth year. 
While the majority of the Fraser River run are in their fourth year as shown by 
the evidence here adduced, a considerable number of them, including all the larger 
individuals, are just as evidently in their fifth year. The 4-year fish show, outside 
the nuclear area, three summers’ growth and two winters’ growth in the sea. The 
5-year fish, as shown in plate viii, figure 14, have just as distinctly, outside the nuclear 
area, four summers’ growth and three winters’ growth in the sea. As is given in a later 
table, there is a wide overlapping in size of the 4 and the 5 year fish, but all the smaller 
specimens are 4 years and all the larger are 5 years old. The specimens examined and 
