4 BULI^ETIN OF THE BUREAU OF FISHERIES. 



In a recent paper Fraser (1917) has verified some of Gilbert's findings and has 

 extended the study to the spring salmon found in the Straits of Georgia. He has 

 worked out quite conclusively the rate of growth during the life in the sea and also the 

 time of formation of the winter check. 



The present study is a continuation of that begun by Gilbert, and the results thus 

 far have been in perfect agreement with his, although the material has been much more 

 abundant and diverse. The outline of the life history of the chinook as given by him 

 may be almost indefinitely extended, but it seems most unlikely that results may be 

 obtained which are not in agreement with his original conclusions. 



At the beginning of this investigation it was supposed that an examination of the 

 adult scales would give the data necessary for an understanding of the life history. 

 Most of the summer and autumn of 1914 was, therefore, spent on the Columbia River col- 

 lecting scales and data from adult fish. Small series of young, seaward migrants, were 

 also taken at Astoria and Ilwaco, at the lower end of the Columbia estuary. Several 

 collections of adult scales taken at spawning stations on various tributaries of the 

 Columbia and Sacramento Rivers and collections of yearling chinooks made at Baird, 

 Calif., were available for study through the courtesy of Dr. C. H. Gilbert. Access 

 was also had to a collection of j^oung migrants from the Sacramento River through the 

 kindness of N. B. Scofield, of the California Fish and Game Commission. These various 

 collections were studied during the winter and spring of 1914-15. It was possible to 

 verify the main conclusions reached by Gilbert (1913), as follows: (i) The scales present 

 two types of nuclear growth — one, the stream type, indicating that the fish migrated 

 to the ocean after spending one year in fresh water, and the other, the sea type, indi- 

 cating that the fish migrated as a fry; (2) the chinobk may reach maturity at any time 

 between the second and the seventh year. Those maturing in the second or third year 

 are exclusively males." The prevailing ages at which maturity is reached by the chi- 

 nooks of the Columbia River are 4 and 5 years, although fish in their sixth year are fairly 

 common. Specimens maturing in their seventh year are very rare. 



Although it was possible to distinguish typical specimens of the two types of nuclear 

 growth, it was found that there were many modifications of both types which were 

 often confusing, although at the same time they were very significant. In the case 

 of the young migrants taken in the Columbia estuary, the scales showed a well-defined 

 area of narrower rings succeeded by a marginal band of wider rings. (See PI. II, fig. 5.) 

 At first it seemed that these fish must be in their second year; but this conclusion was not 

 considered tenable, since, if this were true, the amount of growth which had taken 

 place during the second year would be surprisingly small compared with that taking 

 place in other cases where there was no doubt as to the proper interpretation of the 

 scales. It seemed much more likely that the wide marginal rings represented a period 

 of vigorous growth initiated by the young migrants on reaching the brackish water of 

 the estuary. The problems presented were so complex that it was considered impera- 

 tive that a careful study be made of the young migrants before proceeding further with 

 the study of the mature fish. 



To this end the writer undertook in the spring of 191 5 the collection of the neces- 

 sary data. As a result of unavoidable delay in getting a suitable net for this purpose, 



<* More recently females have been seen maturing in their third year, but in every case the scales indicated unmistakably 

 that the fish had migrated as a fry. This is an important point for future consideration. 



