LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



105 



Table 19. — Comparison of growth of lake herring, by age groups, taken in pound nets at the same time of year at different 



locations 



[Calculated total length In inches] 



equal in the two areas. Differences between 

 growth of lake herring from northern and southern 

 localities are much more apparent in the calcu- 

 lated lengths. Without exception northern fish 

 grew less in their first year than did southern 

 fish. Although growth increments of the northern 

 fish were predominantly larger than those of 

 southern fish in the second year and were without 

 exception greater in the third year, the initial 

 handicap of slower growth in the first year was 

 overcome by the end of the third j^ear of life in 

 only 2 of 10 pairs of samples. By the end of the 

 fourth year, however, the initial differences in size 

 in the two areas had largely disappeared. 



The significance of this comparison may be 

 questionable in the light of information brought 

 out in a later discussion (Growth Compensation, 

 p. 109), that fish with poor first-year growth also 

 tend to be slightly shorter at capture than fish 

 having better growth in the first year. It is 

 possible then that differences between calculated 

 lengths of lake herring in northern and southern 

 samples may be a reflection of differences in the 

 length at capture. That such an explanation is 

 not adequate is indicated, however, in the data of 

 table 20 which gives comparisons of the growth 



histories of fish of the same age in the same }^-inch 

 length interval. Northern Green Bay fish of the 

 same length and age as the southern Green Bay 

 fish at capture tended to be shorter than the 

 southern at the ends of their first, second, and 

 third years of life; but after the first growing 

 season northern fish usually grew more than 

 southern fish. This similarity of growth differences 

 in selected length intervals and entire age groups 

 is evidence that northern and southern fish do 

 have different patterns of growth. The hypothesis 

 of a north-south gradient is suggested by the fact 

 that differences in first year's growth are greater 

 in samples taken farther apart. 



Annual fluctuations in growth rate 



Since calculated growth histories of lake herring 

 in Green Bay differ according to season and geo- 

 graphical location, studies of annual fluctuations 

 in growth must be based on samples taken in the 

 same location at the same time each j'ear. The 

 series of samples that best met these require- 

 ments were taken in the southern part of Green 

 Bay in January or February in the years 1949 to 

 1952. The materials for the study of annual 

 fluctuations in the growth based on these coUec- 



