Table U, - Average calculatca first grov^th incroni<:;nts , by year classes 



Year 

 class 



Averagfe calculated length for fish cnllected In season of - 



1939-hO 



Unad 



HSl 



Aa.i«^ 



2r 



19U0-U1 



ir. 



Vnal1t~^' A-s1t- 



TT 



Unadi.J=/t Ad,1-.£ 



-2r 



1932 

 1933 

 193U 

 1935 

 1936 

 1937 

 1938 

 1939 

 19U0 



111.83 

 llU.02 

 102.22 

 10U.U9 

 97.95 

 113.91 

 115. lU 



99. U 

 llU.U 

 123.6 



108.97 

 115.20 

 107. OU 

 107.62 

 101.98 

 113.76 

 108.93 

 102.66 



103.0 '• 



llh.l « 



118.5 « 



102.0 * 



110.00 

 111.26 

 106. U8 

 103. 81| 

 102. 7U 

 112.03 

 99.89 

 92.91 

 116.73 



10U.3 



113.6 



113.0 



92.0 



i' Unadjusted figures. 



£/ Adjusted for deviations from exact proportionality of scale length to 

 body length. 



It is reasonable to expect that all thoso causes •vJould be progressive 

 and rather regular in their effect, resulting In constant increase, or decrease 

 in comparable values of t with increase of age. Also, this trend should be 

 continued in the collections of later years. 



,It is apparent at once from table U, hovfever, tnat far from progress- 

 ing regularly, the comparable values of t fluctuateci' with no evident order 

 in each of the three years of data studied. Thus it seems improbable that 

 the fluctuations could be associated vdth age. On the other hand, it does 

 appear that they are associated v.-ith year classes. If so, any given growth 

 increment (^) of a given year class should deviate from a norm of that in- 

 crement in the same direction every yoar, as long as that class is wholly 

 and significantly represented in the samples v;:th respect to the increment 

 in question. The meaning of this will become clear presently. 



To establish a norm for "^j^, the 1- values for year classes 1932 to 

 1938, inclusive, v;ere averaged, using €ho material collected during the 

 season of 1939-UO, and these grand averages vrere taken as norms for that 

 season. Deviations of the 1^ values for individual year classes were then 

 plotted as curve number one in figrore 6. The same procedure was follovrcd 

 VTith the material collected in the next sodson (I9UO-UI), furnishing a 

 second curve in figiu^e 6. Although an additional year class, that of 1939, 

 was present, it did not enter into that season's norm; but the deviation 

 of its ^1 value from the norm is indicated by a dotted line. Next the ma- 

 terial collected in 19U1-U2 was similarly treated and the results plotted 

 in the third curve of figure 6. Year class 1939 was not included in the 

 norm, but deviations of its Tj value is indicated in figure 6 by dotted lines. 



Ill 



