LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



131 



Table 42.— Water temperature at or near experimental gill-net stations 

 [Temperature records made with a bathythermograpb. Depth of cast (feet) is Indicated by deepest temperature recorded] 



I See figure 1 for location. 



where the temperatures on July 23 and 24 were 

 19.7° to 20.5° C. In October when the lake 

 herring were again most plentiful from the surface 

 to 30 feet, the water temperature was generally 

 cool (8.1° to 10.2° C.) and the temperature gradi- 

 ents from top to bottom were insignificant (great- 

 est difference 0.4°). 



The one previous study of the vertical distribu- 

 tion of the lake herring in relation to size of fish 

 was made by Fry (1937) in I^ake Nipissing. Fry 

 found that the movement from shallow water to 

 the hypolimnion was not a mass descent but was 

 "* * * an orderly succession of certain groups 

 of individuals which migrate in order of size and 

 sex." Consideration of the distribution in rela- 

 tion to sex was made earlier (p. 120) in the dis- 



cussion of sex composition. In the summary o 

 the length of lake herring taken at various depths 

 (table 43) the sexes are combined, as no sex differ- 

 ences in length were found for fish taken in the 

 same depth of water. Despite certain exceptions 

 (usually at depths in which the catches were small) 

 the average size of lake herring tended to decrease 

 with increase in depth of water in all collecting 

 periods. Davidoff " found a similar tendency for 

 the larger ciscoes of Myors Lake, Indiana, to be 

 near the surface. 



The seasonal changes in the distribution of the 

 lake herring must be a major cause of the highly 



" Davidofl, Edwin B. 1953. Growth, response to netting, and bathy- 

 metric distribution of the Cisco. Levcichthysarledii (Le Sueur) In Myers Lake. 

 Indiana. M. S. thesis. Department of Fisheries. University of Michigan. 

 (Typewritten.) 



