LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



119 



Table 33. — Changes in sex composition icilh age for different lake herring populations 



[Number of fish in parentheses] 



Table 34. — Sea; composition of lake herring taken in pound nets, 1948-5B 

 [Number of fish in parentheses; males at left, females at right] 



' Includes flsh of unknown age. 



diflFerencc in th(^ percentage of females appears in 

 the data for individual age groups as well as in the 

 data for all ages combined. 



The percentage of females in samples of lake 

 herring taken from pound nets also showed a 

 clear tendency to decrease during the period 1949 

 to 1952 (table 84). This trend is present in the 

 best-presented age groups (III and IV') as well as 

 in tlie data for all ages combined in both the 

 Januarv-P\'l)ruarv samples and the samples from 

 the remaining montlis. 



The change in sex composition witli increase in 



age of lake herring taken in pound nets was irreg- 

 ular, but a downward trend in the percentage of 

 females is evident in most series (table 34) and is 

 conspicuous where data of all years for compara- 

 able periods have been combined (bottom of 

 table). This trend would suggest that young 

 females might be taken in the pound-net fishery 

 at a higher rate than young males. A sex differ- 

 ence in mortality of this kind should result in a 

 progressive reduction in the proportion of females 

 within a year class. That this expectation is 

 fulfilled consistentlv in the January-February 



