262 BULLETIN OF THE BUREAU OF FISHERIES 



in their second year, and a significant number of both males and females return in 

 their third. No 6-year-olds have been recovered as yet. From the standpoint of 

 growth, however, there is very little difference Ln the time of maturing; that is, the 

 two classes mature after appro.ximately equal intervals of rapid growth. The rate of 

 growth in fresh water is so low, in comparison to that in the ocean, that a year of fresh- 

 water growth is insignificant in comparison to two or more years of ocean growth. 

 The size attained, therefore, is proportional to the length of time spent in the ocean. 

 The fall chinooks normally enter the ocean early in their first year, whereas the 

 spring chinooks remain in the streams for an entire year before going to the ocean. 

 In addition, the former remain in the ocean for three or four months of the rapid- 

 growing season of the year in which they mature, whereas the spring chinooks start 

 their spawning migration so early in the year that they make little or no growth 

 during the last season. As a result of the earlier seaward migration and later spawn- 

 ing migration the fall fish spend approximately one full growing season more in the 

 ocean than do the spring chinooks of the same age and have spent about the same time 

 in the ocean as spring chinooks one year older. The relation between ocean residence 

 and time of maturing is therefore about the same for the two classes. 



HOMING INSTINCT 



The so-called "parent-stream" theory or "home-stream" theory is now sub- 

 stantiated by such a wealth of evidence that it seems nearly superfluous to state that 

 none of the salmon marked on the Columbia have been recovered in any other river 

 system. 



The records of marked Columbia River chinooks taken off the coast of British 

 Columbia and southeastern Alaska show something of the wide oceanic migrations 

 of these fish and are in agreement with the results of the tagging experiments. The 

 tagging experiments in British Columbia in 1925 (WilUamson, 1927) showed conclu- 

 sively that a large percentage of the spring (chinook) salmon caught by troll in these 

 northern waters originated in the Columbia River. In view of this wide range in 

 the ocean, the fact that no marked fish were reported in any other stream than the 

 Columbia indicates clearly the force and discrimination of the homing instinct as it 

 affects the return to the home stream. 



It is evident, furthermore, that under normal circumstances salmon predomi- 

 nantly return to spawn in the tributary in which they spent the early part of their 

 lives, although they have been shown not to do so in some instances. It is important 

 to note, in this connection, that the transplanted fish have shown no tendency to 

 return to the stream from which the eggs were taken. The homing instinct is not a 

 purely hereditary matter, therefore, but is determined largely by the early environ- 

 ment. These experiments have shown that under certain circumstances the return 

 to the home tributary is by no means invariable and that the major part of a run may 

 fail to return to the tributary in which it was reared and hberated. Experiment 

 No. 7 gave the most conclusive evidence on this point. Nearly half of the 252 adults 

 recovered from this experiment were taken in the Columbia River several miles above 

 the mouth of Tanner Creek, where the fingerhngs were hberated. As only three 

 were taken in Tanner Creek, it is apparent that the majority chose not to enter that 



