EARLY HISTORY AND SEAWARD MIGRATION OF CHINOOK 

 SALMON IN THE COLUMBIA AND SACRAMENTO RIVERS. 



By WILLIS H. RICH, 

 Field Assistant, U. S. Bureau of Fisheries. 



INTRODUCTION. 



HISTORY OF THE INVESTIGATION. 



The present study of the chinook salmon {Oticorhynchus tschawytscha) , of which this 

 paper forms the first contribution, was started in the summer of 1914 at the instance of 

 the U. S. Bureau of Fisheries. The importance and necessity of such a study had been 

 made apparent, especially by the work of Gilbert on the sockeye salmon, and it seemed 

 advisable to extend in detail the outline of the hfe history of the chinook as given 

 by Gilbert (1913). The method employed — that of analysis on the basis of scale 

 studies — is now too well known and too widely used to need description. The paper 

 just cited and subsequent studies of the sockeye by the same author contain a complete 

 description of the methods emoloyed and form admirable examples of studies prosecuted 

 on this basis. 



Our knowledge of the life histories of all the Pacific coast Salmonidae was dis- 

 tinctly unsatisfactory previous to the discovery of the value of scale studies. The 

 descriptions given by Jordan and Evermann (1896-1900), Jordan (1905), Rutter 

 (1903), Scofield (1898), and Chamberlain (1907), contain the most accurate informa- 

 tion regarding the chinook which was available prior to Gilbert's first study. The 

 general features of the early life in fresh water and of the seaward migration were well 

 known, and Chamberlain had shown quite conclusively that the sockeye and chinook 

 salmon mature commonly at about the fourth year, although this is subject to variation. 

 The work of McMurrich (1912) on the chinook salmon, based on the scales, has been 

 shown by Gilbert (191 3) to be imreliable because of the small number of specimens 

 examined and an incorrect interpretation of the central (nuclear) area of the scales. 



It remained, therefore, for Gilbert (1913) to give us the first accurate description 

 of the general features of the life history of the chinook salmon in his paper, "The Age 

 at Maturity of the Pacific Coast Salmon of the genus Oncorhynchus." In this he shows, 

 among other things, that: (a) The chinook, or king, salmon spawn normally either in 

 the fourth, fifth, sixth, or seventh year, the females more frequently in the fourth year; 

 (b) the "grilse" are exclusively males and are of two sizes, representing two and three 

 year fish; (c) the young may migrate as fry soon after hatching, or may remain in the 

 stream until their second spring, migrating as yearlings; and {d) among the fish of any 

 given age, the larger specimens will be those which migrated seaward as fry, although 

 these do not attain the average stature of those fish, one year older, which migrated 

 as yearlings. 



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