LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



135 



where W is weight in ounces and L is total length 

 in inches. 



19. Weight varied according to sex and to 

 method, season, and year of capture. 



20. Females were relatively more abundant in 

 samples taken from pound nets in February than 

 in May to December. They were also more 

 plentiful in the younger age groups than in the 

 older. The selective destruction of females in 

 younger age groups may be a major factor in the 

 progressive decline with increased age in the 

 percentage of females in a year class. 



21. The percentage of females in the Green 

 Bay lake herring population declined continuously 

 from 1949 to 1952. 



22. The percentage of females in collections 

 taken in oblique sets of gill nets increased with 

 depth of water in October. This change in sex 

 composition with depth may reflect an actual 

 difference in the distribution of the sexes, but a 

 difference in the activity of the sexes may have 

 been a major factor. 



23. Some Green Bay lake herring matured 

 during their second year of life, and all had reached 

 maturity by the end of the third year. 



24. Lake herring spawn in Green Bay between 

 mid-November and mid-December, but spawning 

 of an individual school of fish may be completed 

 in a fraction of this period. Fish of the same 

 school do not necessarily complete spawning in 

 one location. Within a school, the older fish 

 and the larger fish of an age group tended to 

 spawn first and the males spawned earlier than the 

 females. 



25. Lake herring are pelagic spawners; the eggs 

 are broadcast and settle unprotected to the 

 bottom. Inshore areas are preferred, but there 

 is evidence that lake herring may spawn in Green 

 Bay over water as deep as 140 feet. 



26. The literature indicates that lake herring 

 hatch in early spring (April-May) and that newly 

 hatched fry are pelagic. Young-of-the-year lake 

 herring have rarely been collected. They prob- 

 ably lead a bathypelagic existence where they are 

 relatively immune from capture by the usual 

 methods of collection. 



27. Although the number of eggs produced by 

 female lake herring (range, 3,471 to 11,212) varied 

 widely for fish of the same total length as well as 

 of different lengths, the number of eggs tended to 

 increase with length of the fish. The relative 

 number of eggs (i. e.. number per ounce of bodv 

 weight) tended to decrease with increase of length. 



28. The lake herring of Green Bay were ran- 

 domly distributed from top to bottom in early 

 May, but they were concentrated in the upper 15 

 to 30 feet in late May. They descended to deeper 

 water in June and were restricted to strata more 

 than 30 feet below the surface in July when tem- 

 peratures in shallower water were unfavorable 

 (17° C. and above). In October, lake herring 

 were again found at all levels but were most 

 abundant in the upper 30 feet. 



29. Lake herring are not migratory but they 

 sometimes move considerable distances to avoid 

 unfavorable temperatures. Local movements are 

 probably associated with feeding or represent 

 passive transport by currents. 



