SEAWARD MIGRATION OF CHINOOK SALMON. 



59 



specimens whose scales show the marginal band of wider rings indicative of the new 

 growth of the second year. 



The "primary check" which has been noted on the scales of the Columbia River 

 fish does not appear conspicuously in the Sacramento series. In the case of the fish 

 from the lower part of the river this is not surprising, since such a primary check has not 

 been found on the scales of specimens from the lower part of the Columbia until autumn, 

 considerably later in the year than the last collection from the lower Sacramento. The 

 absence of the primary check in the collections from the McCloud may well be a racial 

 characteristic, just as the presence of such a check is a racial characteristic of the young 

 fish in the McKenzie River. (Compare PI. I, fig. 8, a scale from one of the McKenzie 

 River fish, with PI. Ill, fig. 9, a scale from one of the McCloud River specimens.) 



Table 50 gives the data, averaged for each month, for the collections from the lower 

 part of the river. Table 51 gives the data for the collections from the McCloud River. 

 Graph 8 gives the data regarding scale growth based on all the available data from the 

 Sacramento River system. In this graph the line representing the growth of the fish 

 is the same as the generalized curve developed in graph 3. 



Table 50.— Rats of Growth and Scals Development in Lower Sacramento River. 



Month. 



March 

 April. 

 May.. 

 June.. 

 July.. 



Length. 



Mm. 



37-2 

 50.8 

 72-7 

 77-3 

 92.3 



Average 



number of 



rings. 



4-S 

 9.1 

 9.6 

 14.8 



Average 



length of 



anterior 



radii. 



"•3 

 33-7 

 34-1 

 47-9 



Table 51.— McCloud River: Average Length and Scale Development for Each Month. 



1 Without new growth. 



b With new growth. 



