- 30 



Table III. Standard deviation for seven samples examined 

 by seven different persons. 



The table shows, that a, for all the year-classes, is here considerably less 

 than in the whole of the material for 1913 — 14. Although erroneous determina- 

 tions of age naturally play some part in occasioning variation, it is nevertheless 

 evident that such errors cannot suffice to account for the whole extent of 

 variation observed. 



Methods of capture. 



The samples examined having been taken partly from catches made with 

 the net and partly from seine-caught fish, the question arises as to whether this 

 difference in the method of capture may be responsible for some part of the 

 variation found. In order to investigate how far this may or may not be the 

 case, it is necessary to have an amount of material from which accurate com- 

 parisons may be made between seine and net catches taken at the same place 

 and time, in addition to which, it will be requisite to take into consideration 

 the one characteristic feature which is of primary importance in comparing the 

 effects of the implements used, viz. the size, which determines whether a fish 

 is taken by the net or permitted to escape. Table IV shows the average sizes 

 for d* and Ç in pairs of samples taken by net and seine respectively, and in 

 so close propinquity of time and place as to render such comparison sufficiently 

 legitimate. 



Table IV. Net and seine catches made at approximately same place and time, 

 year-class 1904 being the material selected. 



This table does, as a matter of fact, seem to indicate a slight diffe- 

 rence in length between net and seine caught fish, the latter being apparently 

 a little smaller. The seine catches, where the implement used exercises no selec- 

 tion, must naturally be considered as the more truly representative as regards 

 composition in point of age and size: this table therefore leads us to the con- 

 clusion that the net catches will be relatively somewhat too largely composed of 

 bigger, and consequently older, fish. It is impossible to determine, however, on 

 the basis of the facts as at present ascertained, the importance of these condi- 



