SEAWARD MIGRATION OF CHINOOK SALMON. 5 1 



There is here merely the upper end of a curve of growth which began in the early 

 months of the year, when the fry were 35 to 40 mm. in length. The earlier part of the 

 curve is undoubtedly represented quite accurately by the data obtained from the col- 

 lections from the lower part of the river. 



In graph 3 the lines give a generalized curve combining the data from the two 

 regions of the Sacramento. The dotted line represents the probable growth of McCloud 

 River fish during May, June, and July. This curve represents approximately the normal 

 rate of growth in the Sacramento Basin. It is interesting to note that the indications 

 are quite clear that the growth of the migrating fish does not slow up during June and 

 July, as is the case with the fish from the McCloud River. It is more than likely that the 

 yearlings in the McCloud River would begin to show the slower growth in May if data 

 were available. 



The single collections from the coastal streams offer no basis for the analysis of 

 growth. The collections from the Siletz, Trask, Nehalem, and Nestucca Rivers average 

 about the same as those taken at the same time of year from the Sacramento and Colum- 

 bia Rivers. The rate of growth in these streams is, therefore, probably about the same 

 as in the larger rivers. The collections from the Bear, Tittle, Shasta, and Sixes Rivers 

 and from Deer, Flores, and Elk Creeks average smaller in size than the collections from 

 the Sacramento and Columbia Rivers. It may be concluded that the rate of growth 

 in these streams is slower than in the others studied. Any conclusions, however, based 

 on such scanty material must necessarily be merely tentative. 



It may be stated in a general way that the growth of young chinook salmon in 

 fresh water is most rapid during the first three or four months after the appearance of 

 the fry. The time of year during which this rapid growth takes place varies in different 

 streams, according to the time at which the fry make their appearance. The prevailing 

 temperature of the water is also an important factor. After this first period of rapid 

 growth the rate rapidly decreases during another period of about three months, until 

 finally growth practically ceases for the year. A new period of rapid growth is appar- 

 ently begun during the early months of the second year in case the fish remain in fresh 

 water. 



At the time the yolk sac is absorbed and the fry become free-swimming the average 

 length is between 35 and 40 mm. By the end of the first period of most active growth a 

 length of 80 or 90 mm. has been attained. The average length attained during the entire 

 first year is approximately 100 mm. 



The effect of migration into the brackish water of the estuary is to decidedly 



stimulate the growth. 



DEVELOPMENT OF SCALES. 



This section, dealing with the development of the scales, is, in certain respects, the 

 most important part of this study. The work on the young fish was undertaken pri- 

 marily, as has been previously mentioned, in order to supply an established basis for 

 the interpretation of the nuclear portion of the adult scales. The especial need was data 

 sufficient to permit a reasonably accurate determination, from the adult scales, of the 

 time of migration. To this end are recorded here in detail the data bearing both on 

 ring counts and the length of the anterior radii. The data for the Columbia River fish 

 are given in Table 48 and in graphs 4 to 7. 



