26 



BULLETIN OP THE BUREAU OF FISHERIES. 



year will increase. Since there is no method of distinguishing with certainty between 

 the two types, the marginal band of wider rings found on the scales of the fish taken in 

 the estuary will be referred to as the "intermediate band." In the case of fish from the 

 upper waters, however, where the interpretation is unquestioned, we shall designate 

 the marginal widening as "new growth." 



Such a marginal band of wider rings is not always formed on the scales of fish found 

 in the estuary. It is not apparent on the scales of the smaller migrants owing to the 

 fact that the first few rings formed on the scales are almost always wider than those 

 normally succeeding. They are not, however, wider than the intermediate rings but 

 are of approximately the same width, so that no break appears at the point where the 

 intermediate growth actually begins. The absence of the intermediate band on the 

 scales of some of the larger migrants is probably due to the fact that those fish have not 

 been in the brackish water long enough for the wider rings to have developed. When 

 the intermediate growth is not found on the scales of the adult fish, which show a 

 nuclear area of true stream growth, it probably indicates that during the seaward 

 migration the individual did not remain long in the brackish water but continued the 

 migration so rapidly that typical ocean rings were formed immediately succeeding 

 typical stream rings. 



The following table (19) gives the data relative to the McKenzie River collection: 



Table 19. — Young Chinooks from McKenzie River, Nov. 2 and 3, 1915. 

 specimens without new growth. 



Length. 



Scale record. 



Average number 

 of rings — 



Average length of 

 anterior radius- 



Total. 



With 

 check. 



To 

 check. 



Total. 



To 

 check. 



Total. 



Average 

 estimated 

 length of 

 fish at 

 time of 

 forma- 

 tion of 

 check. 



131 to J25 mm. 

 116 to 120 mm. 

 Ill to 115 mm .. 

 106 to no mm . . 

 loi to los mm. , 

 96 to 100 mm. .. 



91 to 95 mm 



86 to 90 mm 



8i to 85 mm . . . 



Total 



Av. 105.8 mm. 



8.0 

 7.0 

 7-7 

 7-7 

 8-S 

 8.5 

 10. o 

 9.0 



22.0 

 19.0 

 19.4 

 18.7 

 18.3 

 17.0 

 15.0 

 16.0 

 14.0* 



38 



28.0 

 38.0 

 23.0 

 25-5 

 23. o 

 23.0 

 33- o 

 28.0 



58.0 

 63.0 

 49.3 

 53-5 

 48.0 

 45-5 

 63.0 

 58.0 



SPECIMENS WITH NEW GROWTH. 



