260 BULLETIN OF THE BUEEAU OF FISHERIES 



a nuclear area composed in part of stream growth, with fine, narrow rings, and in 

 part of ocean growth, with wide, strongly marked rings. This is amply explained by 

 the habit of the young fish in the Columbia of migrating throughout the year and not, 

 as in many other cases, during a definite and restricted season (Rich, 1920). Ac- 

 cording as the length of time in fresh water is short or long, the amount of stream 

 growth is less or greater; in the first instance the nuclei approach the ocean type 

 and in the second they approach the stream type, and the intergradations appar- 

 ently are complete. For these nuclei, composed in part of stream and in part of 

 ocean growth, we propose the term "composite nuclei." 



A further complication arises as a result of the presence on many scales of 

 "intermediate" growth — that formed during the life in the estuary while on the 

 seaward migration. The rings formed at this time are "intermediate" in position 

 and in appearance between the stream and ocean rings and vary so materially that it 

 is difficult to distinguish them with certainty, sometimes from the stream rings and 

 at other times from the ocean rings. Nuclei composed only of stream rings and 

 intermediates blend indistinguishably with certain types of composite nuclei. 



As a result of these variations the first year's growth on the scales of Columbia 

 River chinooks frequently is very confusing and presents, in extreme cases, as many as 

 four or five checks, each of which might easily be mistaken for an annulus by an 

 inexperienced observer. As a matter of fact, however, with experience this confusion 

 is eliminated almost completely, at least in so far as the determination of age is con- 

 cerned. It may never be possible to interpret correctly the details of history recorded 

 in a complicated composite type of nucleus, but that is relatively immaterial for 

 practical purposes as long as there is no error in age determination, and our experience 

 with the scales of fish of known history has provided sufficient information so that 

 such errors raiay be eliminated almost entirely. 



TIME OF ENTERING FRESH WATER 



Perhaps the most important contribution which these experiments have made to 

 our knowledge of the biology of the salmon is that relating to the hereditary char- 

 acter of the factors that determine the time of year when the adults enter fresh water 

 and begin their migration to the spawning grounds. The great practical value of 

 determining beyond question whether this is strictly an hereditary character or not 

 is associated with the fact that the early run of chinooks (spring chinooks) is of much 

 better quality and is, consequently, of much greater value to the fishery than the 

 later run (fall chinooks). The spring fish are sought most earnestly, and the main- 

 tenance of the spring run has been the chief concern of those interested in practical 

 conservation. This question has been asked frequently: Is it necessary to breed from 

 fish of the spring run in order to produce spring fish, or is it possible, by proper han- 

 dling of the progeny of the fall run, to produce fish that will return as adults to fresh 

 water early in the spring? 



The evidence of these marking experiments shows beyond question the heritable 

 quality of this character. In 8 of the 13 experiments the young fish were derived from 

 eggs taken either on the Willamette River or its tributaries, the McKenzie and the 



