LAKE HERRING OF GREEN BAY. LAKE MICHIGAN 



121 



Table 36.- — Sex composition of lake herring taken al various depths in experimental S-inch-mesh gill nets in 195S 



(Number of fish In parentheses] 



I 



• See figure 1 for location. 



' Depths intervals 0-20 and 20-10. 



Despite the clear-cut change in sex composition 

 with increase of depth, the vaHdity of an assump- 

 tion that sexes are segregated according to depth 

 in October is questionable. Since the gill nets 

 used to obtain these collections were stationary 

 the activity of the fish was a primary determinant 

 of the number of fish taken by them. Accordingly, 

 it is possible that changes in sex composition with 

 depth do not reflect a corresponding difference in 

 the actual relative abundance of males and females 

 but that they are merely "apparent changes" 

 traceable to sex differences in activity. In other 

 words, the males may have been much more 

 active than the females near the surface, whereas 

 the activity of the sexes may have been equal or 



nearly equal at the greater depths. No evidence 

 on the question of sex differences in activity is 

 available from the present study or from published 

 reports on the lake herring. Evidence has been 

 published, however, that the males of the related 

 kiyi of Lake Michigan become much more active 

 during the spawning period (Hile and Deason, 

 1947). If a similar behavior is assumed for the 

 lake herring, and if it is assumed further that the 

 heightened activity of males starts in advance of 

 the spawning period and that the fish near the 

 surface are the ones closest to the spawning state 

 (the lake herring is a pelagic spawner), then sex 

 tlifferences in activity rather tlian true segregation 

 can explain the relation of sex composition of lake 



