240 BULLETIN OF THE BUREAU OF FISHERIES 



This was the first experiment in which any number of the adult marked fish 

 returned to the tributary in which they had been liberated as fingerlings. There 

 appears here to be some significance in the fact that the fingerlings were liberated 

 in their native tributary. In most of the other experiments the fingerlings were 

 liberated in a tributary other than that from which the eggs were secured. Even 

 in this experiment the homing was not perfect, as is shown by the recovery of one 

 of the fish in the Big White Salmon River. 



The nuclei of the scales of the adult fish from this experiment are of particular 

 interest because of their wide variation and the light these variations throw on the 

 interpretation of the scales of wild fish of unknown history. Scales with typical 

 stream and ocean nuclei, representing, respectively, migration to the ocean before the 

 scales are formed and after the first year's growth is completed, are identified easily 

 and offer no particular problems; but as the senior author has shown (Rich, 1920), 

 the seaward migration of chinooks in the Columbia is not confined to these two 

 periods but is distributed throughout the year. In view of this variation in the time 

 of migration one would expect to find corresponding variations in the scales, ranging 

 from the typical stream type to the typical ocean type, with transitional stages 

 having varying proportions of stream and ocean growth. A third possible variable in 

 the nature of the scale rings is to be expected as a result of the intermediate environ- 

 ment of the estuary, under the influence of which the fish grow more rapidly than in 

 fresh water but not as rapidly as in the ocean. Such variations in the scales have 

 been observed. Gilbert draws attention to them in his first paper on the scales of the 

 Pacific salmon (Gilbert, 1913). The senior author, in extending the work of Gilbert 

 to a more comprehensive study of the chinook salmon of the Columbia River, 

 encountered such a wide range of variation in the nuclear types that he found it neces- 

 sary to make a careful study of the seaward migrants before continuing with the 

 study of adult scales. The study of the seaward migrants was necessarily confined 

 to the stream and estuary growth, and it was impossible to trace the growth and move- 

 ment of particular individuals through their life in the ocean. This opportunity to 

 study the scales of mature fish of known age and early history is therefore of great 

 value. 



The nuclei of the scales of all of the adult fish in this experiment have a central 

 portion of closely spaced rings, which is set off from the remainder of the scales by an 

 incidental check formed by a slight narrovdng of the rings or by contrast with the 

 wider rings immediately following. The cause of this check is not evident. Its 

 formation does not seem to have been coincident with marking or liberation, as the scales 

 of the fingerlings at the time of marking had 3 to 5 rings, whereas there were 5 to 13 

 rings when the check was formed. It is sufficient in this connection to note that this 

 incidental check is present in all cases and that the portion inclosed by it is typical of 

 stream growth. 



The area of the scale between this incidental check and the first winter check 

 shows a wide range of variation. One extreme of variation is shown in Figure 49, 

 which illustrates a scale in which the band following the incidental check consists of 



