FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



251 



The time of the season during which commercial fishing takes its toll also has an 

 effect on the age composition of the escapement clue to the fact that the age composi- 

 tion of the fish in a season's run is not constant but varies from week to week. If the 

 commercial catch does not take a constant proportion of each week's run of fish, the 

 age composition of the escapement is very apt to be different from that of the run of 

 fish from which it resulted. Except in instances where an abnormal condition indi- 

 cates the advisability of giving special protection to a certain part of a run, it is con- 

 sidered preferable to have the commercial catch so regulated that it constitutes the 

 same percentage of the run from week to week throughout the season. When the 

 catch is regulated in such a manner, the ago composition of the escapement for a 

 season will closely approximate the age composition of the run from which it is derived. 



The escapement data presented in table 17 are used during each season in the 

 regulation of the fishery, and in addition are also used in the study of the number of 

 fish returning from known escapements, a subject discussed in a later section of this 

 publication. 



The data presented in table 18 are used together with data presented in table 25 

 in the study of the change in the age composition of the runs. This subject also is 

 discussed later. 



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