CHINOOK SALMON MARKING, COLtTMBIA RIVER 259 



Two of the more recent marking experiments were designed to provide an answer to 

 this question. Each of these involved five lots of marked fingerlings, which were 

 liberated at varying ages. None of the fish in these experiments have reached 

 maturity to date and have not been discussed in this report; but even the compara- 

 tively um-eliable records of return from the various experiments herein described 

 give some indication of the relative success of the long and short periods of re&ring. 

 For consideration thereof the experiments may be arranged in groups. Those 

 involving the progeny of the spring run into the Willamette River may be taken 

 as one group. This will include experiments Nos. 1, 2, 5, 6, 7, 9, 10, and 11. In 

 this category the longer periods of rearing have given the best results, virtually 

 no returns having been obtained from fingerlings liberated during midsummer. 

 Experiments Nos. 3, 8, and 12, which involved fingerlings derived from the fall 

 runs into the Little White Salmon and Big White Salmon llivers, form another 

 gi-oup. In this case better results have come from a very short period of rear- 

 ing than from liberating during midsummer. The success of the longer periods 

 of rearing has not been determined for this group. On the basis of what is known 

 of the habits of these two classes of chinooks we might have expected such results 

 as have been obtained. As fingerlings of the spring run normally spend the entire 

 first year in fresh water, best returns would be expected from the longer 

 period of rearing. This is especially true if the fingerlings are forced by unfavorable 

 conditions to leave the river as soon as liberated. In the case of the fall chinooks, 

 which normally leave the stream soon after the yolk sac is absorbed, the shorter 

 period of rearing might be expected to be the most successful. 



INTERPRETATION OF SCALES 



It is hardly necessary now to argue for the validity of the methods developed 

 for determining the age and other features of the life history of salmon by means of a 

 microscopic examination of their scales. These methods already have given abundant 

 proof of their value, especially through the careful and extensive researches of Gilbert 

 on the sockeye salmon. It is important to note, however, that the scales of these 

 fish of known history corroborate fully the theory that the arrangement of the con- 

 centric rings (circuli) provides an accurate record of the previous history. 



Moreover, a study of the scales of these marked fish has aided materially to 

 solve the numy perplexing problems that have arisen in the interpretation of the 

 scales of the chinook salmon, particularly in connection with the early history as 

 recorded in the nuclear area of the scales. Frequent mention of these matters has 

 been made in the discussion of the returns obtained from the various experiments. 

 It has been shown, particularly, that the growth of the first year (the "nuclear" 

 growth) is subject to numerous variations, which intergrade so completely that it is 

 impossible to draw any sharp line of distinction. At one end of the series we have 

 the typical stream nucleus, denoting that the first year was spent entirely in fresh 

 water, and at the other end the typical ocean nucleus, denoting that the fish ran out to 

 the ocean immediately after emerging from the gravel of the spawning beds and 

 spent the entire first year there. The majority of the Columbia River chinooks, 

 however, have neither typical stream nor typical ocean nuclei but apparently have 

 spent part of the first year in fresh water and part in the ocean. The result has been 



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