122 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



herring to depth in October samples which were 

 taken about 3 weeks before spawning starts. 



AGE AND SIZE AT MATURITY 



A lake herring was considered immature if it was 

 not in spawning condition when captured during 

 the spawning season, or if the state of the gonads 

 indicated that it would not spawn during the 

 next spawning period following its capture. As 

 most small lake herring captured in Green Bay 

 were taken within a few months before the spawn- 

 ing period, at a time when all mature fish had 

 well-developed gonads, little difficulty was ex- 

 perienced in distinguishing the immature 

 individuals. 



Published statements as to the age at which 

 the lake herring matures frequently have been 

 indefinite because of considerable individual varia- 

 tion among fish and because of questionable 

 dependability of samples as a result of gear 

 selection or segregation on the basis of maturity. 

 Hile (1936) suspected that his estimates of per- 

 centage of maturity in the younger age groups 

 were too high if the faster-growing fish of each 

 age group matured first, since his gill nets did 

 not take the smaller members of those age groups. 

 Van Oosten (1929), who sampled only fish of the 

 spawning run, felt that since immature fish did 

 not participate in spawning activities they were 

 not properly represented in the samples. 



A summary of published data on the maturity 

 of lake herring (table 37) shows that the age at 

 which most fish mature in different populations 

 varies from I to IV. Although lake herring 

 maturing in the first jear of life (age group 0) 

 have never been reported, maturity in the second 

 year (age group I) is common. The reason for 

 later maturity in some populations is not clearly 

 understood . 



The Green Bay collections contained relatively 

 few immature lake herring, all of which were in 

 age groups 0, I, and II (table 38). The two 

 0-group fish taken (one male and one female) were 

 immature. In age group I, 32 percent of the 

 males and 1 1 percent of the females were mature. 

 By the next year (age group II) most fish of both 

 sexes had reached maturity (97 percent of the 

 males; 88 percent of the females). This tendency 

 for males to mature sooner than females was also 

 found in tlic lake lierring of Saginaw Bay (Van 

 Oosten 1929) and Irondequoit Bay (Stone 1938). 



The three 2-year-old ciscoes taken in Lake Ontario 

 by Pritchard (1930) were all mature females. 

 The average lengths of mature and immature fish 

 indicate that the larger members of an age group 

 are more likely to be mature (table 38). 



Table 37. — Age at which lake herring of different popula- 

 tions reach sexual maturity 



(Arranged according to age at maturity] 



Table 38.- 



-Relations among age, lerigth, and sexual maturity 

 in the lake herring of Green Bay 

 [Total length in inches] 



> All flsh older than age group II were mature. 



HATCHING AND EARLY GROWTH 



Almost nothing is known about the incubation, 

 hatching, and early development of lake herring 

 in nature. Cahn (1927) collected unhatched eggs 

 in Lake Oconomowoc, Wisconsin, in March, but 

 had no positive evidence as to the time of hatching. 

 Pritchard (1930) observed that hatching takes 

 place during April and early May in the Bay of 

 Quinte, Lake Ontario, and he made daily collec- 

 tions of the growing fry from May 9 to June 1. 

 These fry were found among reeds in shallow- 

 water areas of protected bays, but apparently they 

 moved toward the open water as they grew. On 

 June 1 when the last individuals were collected, 

 they were 20 millimeters long. After that date 

 tliey could not be located again. Greeley and 

 Greene (1931) collected young-of-the-year lake 



