34 
BULLETIN OF THE BUREAU OF FISHERIES 
run of pink salmon in Anan Creek also appears at practically the same time 
during the season as the run in Snake Creek. If the Snake Creek marked salmon 
strayed any distance from their parent stream in perceptible numbers, it is highly 
probable that they would have been picked up by the trap in the Anan Creek weir. 
However no marked pink salmon were either found in the trap or observed in the 
stream. This, together with lack of recovery of marked pink salmon in any of the 
other more distant streams in the vicinity, makes it rather improbable that the Snake 
Creek pink salmon strayed in perceptible numbers from their parent stream. 
AGE OF PINK SALMON AT MATURITY 
The scales of the pink salmon like the scales of the other species of Pacific salmon, 
tend to grow at a rate proportional to the growth of the fish. This is accomplished by 
the deposition of new material around the border of the scale. Delicate ridges appear 
on the surface of the scale at intervals during its growth which form concentric rings 
separated by spaces of varying width. (See fig. 9.) The variation in the width of the 
spaces between the rings may be attributed to a corresponding variation in the rate of 
growth of the fish. That is during the spring and summer when the fish grows rapidly 
the rings on the scale are widely separated whereas during the fall and winter when 
growth is greatly retarded the rings are crowded together. In this way the surface of 
the scale is marked by bands of widely spaced rings followed by bands of closely spaced 
rings. Since the wide band of rings is formed in the spring and summer and the nar- 
row band in the fall and winter, the two together represent a year’s growth. 
C. H. Gilbert (1913) in his paper “Age at maturity of the Pacific coast salmon” 
pointed out that the pink salmon all mature at 2 years of age as judged by the age 
reading of the growth rings on their scales. He described the pink-salmon scale as 
having three definite bands of growth rings. A central band of widely spaced rings 
of the sea type 10 followed by a band of closely set rings, which is in turn followed by 
another band of widely spaced rings. The first two bands of rings represent the 
growth of the fish during the first spring and summer in the sea and the first and only 
winter in the sea. The second band of widely spaced rings represents the growth of 
the fish during the second spring and summer in the sea. Since the second summer’s 
growth band is never followed by a winter band of rings, Gilbert came to the 
conclusion that the pink salmon always mature at the close of the second year of 
their life. 
Owing to the rapid growth the pink salmon must make, during their 16 or 17 
months’ sojourn in the sea, in order to mature at 2 years of age, some doubt has been 
expressed in regard to their age at maturity as determined from the bands of growth 
rings on their scales. In view of this fact a study was made of the scales on the marked 
pink salmon that were known to return to the Duckabush River and to Snake Creek 
at 2 years of age. The scale pictured in figure 9 is from a marked salmon that re- 
turned to Snake Creek and the scale pictured in figure 10 is from a marked salmon 
that returned to the Duckabush River. These scales were chosen because they are 
representative of the scales of the other marked pink salmon found in these streams. 
The growth rings on the scale in figure 9 may be divided into the three character- 
istic bands described by Gilbert (1913). The first band of widely spaced rings, i. e., 
those laid down in the life of the salmon during its first spring and summer in the sea, 
i° Since the pink salmon fry in most cases leave the streams before their scales have appeared, the only rings that are formed in 
their scales are those that form during their life in the sea. 
