62 



BULLETIN OF THE BUREAU OF FISHERIES. 



The scale growth of the fish from the coastal streams presents nothing miusual or 

 of particular value because of the scarcity of data. Certain racial characters are sug- 

 gested by the data from one or two of the streams, but the evidence does not warrant 

 drawing even tentative conclusions. 



MIGRATION. 



In the preceding sections the matter of migration has been dealt with in only a gen- 

 eral way, and an attempt will now be made to summarize the available facts. 



In the Columbia River migration takes place throughout the year. The fry hatched 

 during the fall and winter may migrate immediately after the yolk sac is absorbed or 

 even before this process is entirely completed, since occasionally specimens which still 

 retained part of the yolk have been found in the estuary. The earliest hatched fry 

 may migrate as early as December, and by March the migration is well under way. 

 The data regarding the time at which the greater proportion migrate are not especially 

 satisfactory, as the accurate determination of this would involve collecting either with 

 some form of stationary gear or by frequent and uniform hauls mth a seine at some one 

 point. Such collecting would need to be continued during each month of the year. 

 The nearest approach that can be made with the present data to a determination of the 

 time of most frequent migration is by finding the average number of fish contained in 

 each collection made in the lower part of the main river (exclusive of the collections 

 made under canneries). This method is subject to considerable error, especially owing 

 to the fact that at the times when the young fish were relatively scarce the collecting 

 was more persistent and more seine hauls were made, on the average, at each point 

 where collections were made, in order to get as large a representation of the migrants 

 as possible. Obviously, such a source of error will tend to broaden the mean time of 

 migration over more time than is actually the case. The data are presented in Table 

 53. The process of "smoothing," by which the figures in the fifth column were ob- 

 tained, is the one commonly used. The smoothed figure for each month is obtained 

 by taking the average of the actual figures for the month in question, plus those for 

 both the preceding and succeeding months. Graph 9 gives the smoothed curve. 



Tablb 53. — Columbia River: Average Number of Fish in Each Collection. 



Month. 



Preening 



column 

 smoothed. 



FRY. 



March 



April 



May 



June 



Jtily 



August 



September 



October 



November 



December 



YSABX.ISGS. 



March 



April 



May 



19- X 

 39-4 

 37-8 

 &9-0 

 73.6 

 89.0 

 73-3 

 65-0 

 46.6 

 10. 6 



