[momurRicu] LIFE CYCLES OF THE PACIFIC COAST SALMON 17 
THE SPRING SALMON, O. tschawytscha (Walbaum). 
The Spring Salmon as caught at the mouth of the Fraser river 
present one peculiarity in marked contrast with the Sockeye, namely, 
that while in the latter the adult fish are of fairly uniform size, with an 
average length of 67 or 68 em., the adult Spring Salmon vary greatly in 
size. Of thirteen fish, selected to give gradations in size, the smallest 
measured 65.5 em. and the largest 112.0 cm. Two still smaller fish, 
measuring respectively 54.0 and 57.5 cm. were also obtained, but, as 
will be seen later, these were evidently grilse. 
This variation in size of the adult fish suggested the possibility of 
corresponding variations in the length of the life cycle, but an examina- 
tion of the scales definitely negatived such an idea and showed clearly 
that the typical cycle for each adult fish, large or small, was one of four 
years, as in the Sockeye. 
THE SCALES. 
The scales from the two grilse of this species closely resemble those 
of the Sockeye grilse. In the photograph (Plate VI. fig. 2), which is of 
a scale taken from a fish 54.0 em. in length, there has been some injury 
of the nuclear region, and the arrangement of the lines immediately 
surrounding it does not show clearly; a few narrow lines can, however, 
be seen succeeding the injured area, and these, as may be seen by com- 
parison with other more normal scales, represent the outermost of the 
rings formed during the early life in fresh water. They are succeeded 
by a wide zone of broad lines and these by a distinct zone of narrow ones, 
the two together representing the growth during the first summer and 
winter in the sea. From this zone of narrow lines to the margin of the 
scale only broad lines occur, representing the second summer’s growth, 
and it was during this summer that the fish was captured. 
The grilse Spring Salmon then, like the grilse Sockeye are two year 
old fish. 
The seales of the largest adult fish examined, a fish that measured 
112.0 em. in length, showed clearly four years of growth and no more 
(Plate V.). Around the nucleus there were, as usual, the narrow lines 
representing the growth in fresh-water, before migration to the sea 
occurred. Then follows a broad zone of broad lines and a narrow one 
of narrow lines, together representing the first year spent in the sea; 
next comes a similar pair of zones representing the second year in the 
sea, and being together even broader than those of the first year, and 
then a third pair, slightly narrower than the first. Finally a narrow 
zone of broad lines represents the fourth summer, during which the fish 
was captured. 
