48 



BUI^LETIN OP THE BUREAU OF FISHERIES. 



It has been shown that new growth is recorded on the scales of fish in tributary 

 streams as early as October or November (p. 25). Since there is no conspicuous increase 

 in the amount of new growth between this time and the following May or June, and 

 since, also, it has been shown that the fish entering the estuary during the late fall or 

 winter may show a marginal band identical with the "new growth" observed in the 

 tributaries, it seems safe to conclude that the young fish start the downward migration 

 soon after beginning the new growth, if not before. This matter is given furthei con- 

 sideration in the sections dealing with scale development and with migration. 



The estimated size at the time of beginning the new, or the intermediate, growth 

 is given in the following table (46) and in graph 2. (Consideration of the collection 

 made at Seufert, which has already been discussed, and of the one made at the Clacka- 

 mas hatchery in December, 191 4, is omitted here.) 



Table 46.- 



-AvERAGB Estimated Length at Time of Beginning New Growth (Groxip 4) or Inter- 

 mediate Growth (Groiips 1,2, and 3). 



There is a distinct grouping of the estimated lengths at the time of beginning the 

 intermediate growth about three modes, as follows: During June, July, and August the 

 mode is approximately 55 mm.; during September, October, and November, approxi- 

 mately 100 mm.; and during the remainder of the time in which the young are taken 

 in the river, approximately 80 mm. This may be an accidental result due to insufficient 

 data; but it is believed that there is something fundamental concerned. The mode at 

 55 mm. agrees fairly well with the length of the young chinooks planted in the pond at 

 Seufert. (See p. 18.) It seems probable, therefore, that the check from which this 

 estimate was made represents some incident in the early history of the fry com- 

 parable with the transfer from hatchery to more natural conditions. Therefore, this 

 estimated length may represent either the size at the time of planting from the hatcheries, 

 the size at the time the fish left the smaller streams on their downward migration, or the 

 size at the time of entering the brackish water of the estuary. The mode at 80 mm. 

 represents the size attained at the time of beginning the new growth of the second year. 



