CHINOOK SALMON MARKING, COLUMBIA RIVER 261 



Santiam, where the spawning runs are composed exclusively of salmon that enter the 

 Columbia early in the spring. The fish were reared and liberated on tributaries of 

 the Columbia that normally are inhabited by fall-running salmon only, but the 

 marked fish returned to the river as adults during the spring. Of the 390 adults that 

 have been recovered from these experiments, 365 were taken before June 1, and there 

 is some evidence that all but two of those taken after that date had entered the river 

 some time before they were caught. These fish not only were subjected to an unna- 

 tural environment during their early lives but also were liberated at various ages, 

 ranging from 7 to 18 months. Neither of these conditions seems to have changed 

 the time of their return to fresh water. 



A converse experiment (experiment No. 13), in which the progeny of fall chinooks 

 were reared and liberated under conditions normal to spring chinooks, has given sim- 

 ilar results. All of 16 mature fish recovered from this experiment started their spawn- 

 ing migration in the fall. 



Another interesting feature of the spawning migration demonstrated by these 

 experiments is the comparatively short time during which the fish from each tributary 

 leave the ocean. As has been pointed out, chinooks that spawn in the Willamette, 

 McKenzie, and Santiam Rivers with but few exceptions enter the Columbia River 

 before the 1st of June. The fish that developed from eggs taken on the Little White 

 Salmon and Big White Salmon Rivers were found to be passing though the com- 

 mercial fishing district in August and September. All the fish in experiment No. 4, 

 which were introduced from the Umpqua River, were caught during a period of less 

 than a month, beginning May 13. It seems fairly clear that the fish belonging to any 

 given tributary enter the main river from the ocean at a definite and characteristic 

 time. This is an important point, as it gives additional evidence of the existence of 

 local races in the tributary streams and shows that each race is present in the main 

 river only a comparatively short time. Knowing, further, that each race is self- 

 propagating, it becomes perfectly apparent that all parts of the salmon run in the 

 Columbia River must be given adequate protection if the rim as a whole is to be 

 maintained. The protection of only one or two portions of the run will not be 

 sufficient, inasmuch as certain races will be left entirely unprotected. 



AGE AT MATURITY 



The relation between the reported returns and the actual returns has varied so 

 greatly as to make only a general consijieration of the age at maturity justifiable. 

 For this purpose the experiments agam may be divided into two classes — those in- 

 volving spring chinooks from eggs taken on the Willamette River and its tributaries 

 and those involving salmon from the Big White Salmon and Little White Salmon 

 Rivers, which enter fresh water during the latter part of the season. 



Mature spring chinooks that were in their third to sixth years have been re- 

 covered. In every case the greatest number matured in their fifth year. The 6-year- 

 olds have always exceeded the 4-year-olds, and the 3-year-olds are represented by 

 only two recoveries. 



The data relating to the fall chinooks are very inadequate, but they indicate that 

 the fourth and fifth years are the prevailing ages at maturity. On the whole, the fish 

 of this class mature one year younger than the spring chinooks. A few males mature 

 105107—29 4 



