LAKE HERRING OF GREEN BAY, LAKE MICHIGAN 



127 



the part this activity plays in the spawning 

 process. Brown and MofTett (1942, p. 149) ob- 

 served ciscoes breaking water in vSwains Lake in 

 the early evening during the peak of the spawning 

 period and remarked, "There was no concentra- 

 tion of these fish. Approximately as many were 

 seen over deep water as were observed over the 

 shallows." The greatest depth of Swains Lake 

 is 64 feet. 



Progress of spawning by age, sex, and size 



Although the lake herring population of Green 

 Bay, taken as a whole, may show irregular prog- 

 ress of spawning, there seems to be some pattern in 

 the progress of spawning of individual segments of 

 the population. The data of the only two samples 

 that contained a good representation of both ripe 

 and spent fish (table 40) show that, without excep- 

 tion, the longer fish tended to spawn before the 

 shorter fish and that the percentage of spent males 

 was greater than that of females. In both sexes 

 the upward trend in the percentage of spent fish 

 with increase of age suggests that older fish 

 spawn earlier than do younger fish. 



Table 40. — Comparison of ripe and spent lake herring in 

 spawning-run collections from Green Bay, by sex and age 

 group, November 2^30, 1950 



[Length in inches] 



Predation on eggs 



Possibly the greatest mortality in the life cycle 

 of lake herring takes place immediately after the 

 eggs are laid. A common predator on these eggs 

 is the lake herring itself. Stone (1938) found cisco 

 eggs in 23 of 34 cisco stomachs collected during 

 the spawning season. Pritchard (1931) found 

 cisco eggs in 6 of 46 cisco stomachs. In Green 

 Bay, 16 stomachs of 19 feeding lake herring taken 

 on November 28, 1950, contained from 1 to 33 

 herring eggs. Although the lake herring com- 



monly eats its own eggs, other species seem to 

 to make greater inroads. Stone found from a few 

 to 200 cisco eggs in stomachs of 20 of 36 brown 

 bullhead (Ameiurus nebiUosus) and believed this 

 fish to be an important predator in Irondequoit 

 Bay. Pritchard noted cisco eggs in the brown 

 bullhead in Lake Ontario, but the yellow perch 

 was a heavier consumer of cisco eggs (average of 

 275 eggs per stomach) during the peak of spawn- 

 ing. He also found cisco eggs in whitefish stom- 

 achs, but the numbers were small as whitefish 

 were not present during the main spawning period. 

 Rawson (1930) also reported that whitefish feed 

 on cisco eggs. Jordan and Evermann (1902) found 

 that the mud-puppy (Necturus maculosus) con- 

 sumes cisco eggs in Lake Erie. These reports of 

 predation on cisco eggs have been mostly inci- 

 dental and have not been based on a special study 

 of this problem. Since lake herring eggs, after 

 being laid, lie unprotected on the bottom, varia- 

 tion in the amount of predation at this stage 

 may influence the relative strength of a year class. 



DISTRIBUTION AND MOVEMENTS 



The distribution of lake herring during the 

 summer months has been a subject of much com- 

 ment in the literature (Cahn 1927; Fry 1937: Hile 

 1936; Hile and Juday, 1941; Koelz 1929; Nelson 

 and Hasler, 1942; Pearse 1921; Reighard 1915; 

 Scott 1931 ; Stone 1938; Van Oosten 1930; Wagner 

 1911). Although the observations of various 

 authors are not exactly comparable because char- 

 acteristics of the bodies of water studied were 

 different, the distribution is similar in all lakes of 

 the same type. Upon the warming of surface 

 waters in the spring the lake herring, a steno- 

 thermic, cold-water animal, avoids this change by 

 vacating shallow water. As warming continues 

 and a thermocline develops, undesirable or intol- 

 erable temperatures of the epilimnion may cause 

 the lake herring to be restricted to the thermocline 

 and hypolimnion. 



In the southern portion of their range lake her- 

 ring are rarely found in lakes that do not develop 

 thermoclines or where the hypolimnion becomes 

 unusually warm. In Indian Village Lake, Indiana, 

 near the extreme southern limit of the range, they 

 have adapted themselves to conditions that might 

 be considered intolerable elsewhere (Scott 1931). 

 In lakes in which either the oxygen becomes 

 depleted or undesirable gases are formed in the 



