AGE AT maturity OF THE PACIFIC COAST SALMON 
5 
tions around its border. At intervals there is produced at the growing edge a delicate 
ridge upon the surface of the scale, the successive ridges thus formed being concentric 
and subcircular in contour, each representing the outline of the scale at a certain period 
in its development. Many of these ridges are formed in the course of a year’s growth, 
the number varying so widely in different individuals and during successive years in the 
history of the same individual that number alone can not be depended on to determine 
age. For this purpose we rely upon the fact that the fish grows at widely different 
rates during different seasons of the year, spring-summer being a period of rapid growth 
and fall-winter a season when growth is greatly retarded or almost wholly arrested. 
During the period of rapid growth the ridges are widely separated, while during the slow 
growth of fall and winter the ridges are crowded closely together, forming a dense band. 
Thus it comes that the surface of the scale is mapped out in a definite succession of 
areas, a band of widely spaced rings always followed by a band of closely crowded rings, 
the two together constituting a single year’s growth. That irregularities occur will not 
be denied, and this is natural, inasmuch as growth may be checked by other causes than 
the purely seasonal one. Also a considerable experience is requisite for the correct 
interpretation in many cases, and a small residue of scales of doubtful significance has 
always remained. This element is too small to affect the general results, and further 
investigation will almost certainly eliminate the doubtful cases altogether. 
SOCKEYE OR RED SALMON (Oncorhynchus nerka). 
[PI. i-m; fig. 14, pi. viii; fig. 22, pi. xn.] 
The sockeye, red salmon, or blueback, as it is variously known, has been assumed 
to mature principally if not wholly in four years, on the basis of the constant four-year 
periodicity in the magnitude of its run in the Fraser River. Richardson is reported as 
having marked young sockeye at Karluk, Alaska, and observed their return at four 
years on the average. Chamberlain marked young hatched from 1902 eggs and planted 
the marked fry in the Naha River, Alaska. The return of adults bearing the appro- 
priate mark was reported in 1906 and 1907, and has continued to be reported for each 
year since that date, including the summer of 1911. If these results are accepted, 
individuals may even reach the age of 9 years before maturing; but this is a conclusion 
so at variance with other evidence and with general probability that complete 
corroboration is required. 
Finally, on the basis of scale and otolith structure, McMurrich announces 4 years 
as the age of adult Fraser River sockeye and 2 years for the undersized or grilse form. 
But as he frankly bases his investigation upon the a priori assumption that Fraser River 
sockeye must be 4 years old, and interprets scale and otolith structure in accordance with 
that assumption, it can hardly be claimed that his conclusion adds anything to our pre- 
vious knowledge. This becomes the more apparent upon an examination of his figures, 
which indicate that he unfortunately chose for examination certain large specimens 
which were in reality 5 years old and not 4. Forced by this method to make an erro- 
neous interpretation of the central area of the scale, all his conclusions are vitiated which 
