LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



115 



Table 27. — Relation between the total length and weight of 

 Green Bay lake herring 



|AU collections combined] 



Table 28. — Seasonal changes in weight of lake herring taken 

 in pound nets in southern Green Bay during 1949 



[Weight In ounces] 



above and the May fish 4.6 percent below the 

 unweighted mean for the tliree dates. The 

 February specimens were sliglitly (0.2 percent) 

 above tiie mean. 



Seasonal changes in weights of fish are often 

 associated with, and are used to follow, the de- 

 velopment and release of sex products. Thomp- 

 son (1942) showed a weight cycle for plaice fol- 

 lowing the spawning cycle, but he pointed out 

 that immature fish also experience a seasonal 

 weight fluctuation similar to that of mature fish. 

 These seasonal changes, he believed, indicate a 

 cycle of relative well-being originating in the 

 variation of conditions that influence the addition 

 or removal of body fat or tissue. 



SEX DIFFERENCES IN WEIGHT 



Because of the demonstrated seasonal changes 

 in weight, studies of sex differences in weight are 

 best made on samples taken within a short period 



of time. Actually the comparisons offered by the 

 data in table 29 are based on collections of single 

 days. On none of these dates were sex differences 

 large. The weights of male and female lake 

 herring of corresponding length were nearly the 

 same in February (males 0.5 percent lighter than 

 females). Females were the lighter in May (1.8 

 percent) but were heavier in October (3.4 percent). 

 Sex differences probably are greater at the time of 

 spawning in the latter part of Xovember; un- 

 fortunately, adequate samples were not available 

 for study of this point. 



Carlander (1945) found no significant difference 

 in condition coefficients of male and female tullibee 

 from Ijake of the Woods. Direct comparison of 

 weights of male and female tullibee from Gull 

 Lake (Eddy and Carlander, 1942) showed the 

 females to be slightly heavier for their length than 

 the males, but the difference was small. These 

 authors did not consider possible seasonal varia- 

 tions in their presentation. Two of four popula- 

 tions of ciscoes in northeastern Wisconsin lakes 

 (collections were made only during the summer) 

 showed no differences in weigiit between sexes; in 

 the other two stocks the males were the heavier in 

 one and the females were the lieavier in the other 

 (Hile 1936). Van Oosten (1929) found little 

 difl'erence between average condition coefficients 



