SEAWARD MIGRATION OF CmNOOK SALMON. 



53 



Table 48. — Fish prom the Columbia River: Average Length and Scale Development for Each 



Month— <^ontinued. 



GROUP 4- 



Month. 



Locality. 



Speciinens. 



Length. 



■With 

 scales 

 with 



rings. 



With 

 new or 



inter- 

 mediate 

 growth. 



Scale record. 



Number of rings — 



To be- 

 ginning 

 of rapid 

 growth. 



Total. 



Length of anterior 

 radius — 



Tobe- 

 pinning 

 of rapid 

 growth. 



Total. 



April 



May 



August. . 

 October. 



Clackamas hatchery. 



do 



Clackamas River 



do 



Little White Salmon River «. 

 McKenzie River <= 



Clackamas hatchery. 



November. . . 

 December . . . 



YSARUNCS. 



Jime Clackamas River. 



Mm. 

 46-5 

 49- S 



XI3-9 



1 18.0 

 92.5 



106.4 



Per cent. 



lOO-O 

 lOO-O 

 lOO-O 



100. o 

 100. o 



lOO-O 



Per cent. 



CO 



0.0 

 0.0 

 14.0 



0.0 

 27-0 



20.0 



<> IS- 7 



5-4 



5-9 



30. 7 



30.6 

 25-0 



lS-8 

 18. s 

 19' 8 

 20.0 



34- O 



58.0 



43-4 

 63-7 



73.6 



o Without new growth. 



6 With new growth. 



^ These collections are given with the Clackamas series for the purpose of comparison. 



The chief generalizations derived from the data recorded here are: 



1 . The increase in the number of rings on the scales and the increase in the length 

 of the anterior radii are proportionate to the increase in length of the fish. 



2. Hatchery-reared fish develop scales with rings earlier than do wild fish. 



3. The length of those fish whose scales show a marginal band of wider rings (inter- 

 mediate or new growth) is usually greater than that of fish taken at the same time and 

 place, but whose scales do not present such a marginal band. As a corollary to this, 

 the length of the scales and the total number of rings are greater in those fish which 

 have started a period of active growth than in those, taken at the same time, which 

 have not done so. 



4. The number of rings in the intermediate band (or the band of new growth in 

 Group 4) and the width of this band are somewhat greater in the spring yearling migrants 

 than in the fall fry migrants. 



5. This increase in the size of the intermediate (or new) band is not due to an in- 

 crease in the size of the fish, which is not apparent, but to the fact that the part of the 

 scales central to the beginning of the intermediate band is smaller in the spring than in 

 the fall fish. This indicates that the fall migrants are larger before beginning the inter- 

 mediate growth than are the spring migrants and is indicative of the earlier migration 

 of the larger fish noted elsewhere. 



6. In collections which contain both specimens whose scales show the intermediate 

 growth and those which do not, the number of rings and the length of the anterior radius 

 are less to the beginning of the intermediate growth than to the periphery of the scales 

 on which such growth is not present. Since the fish which have not begun the inter- 

 mediate growth have, in all probability, entered the estuary more recently than those 



