268 
BULLETIN OP THE BUREAU OF FISHERIES 
individual. Fish that would have spawned the following autumn could be distin- 
guished easily from those which would not have spawned at that time. The for- 
mer were considered here as matured fish even though they may not have spawned 
previously. 
Sexual maturity occurs at an early age in each of the four populations. All the 
Clear Lake fish with the exception of a few I-group individuals were mature or matur- 
ing. Since there is good reason to believe that the I-group samples from Clear Lake 
are representative, it may be concluded that in this population the first spawning 
occurs in the autumn of the second year of life. Practically all the I-group indi- 
viduals in the samples from Trout, Muskellunge, and Silver Lakes would have 
spawned the following autumn. There is reason to believe, however, that in these 
populations the nets used for collecting the samples took only the larger I-group 
individuals. The smaller members of the age group may have been immature. In 
all three populations, however, all II-group individuals indicated that they would 
spawn in the autumn. 
The ciscoes of the four populations considered in this investigation attain sexual 
maturity at an earlier age than has been found by some investigators of this species. 
Clemens (1922), referring to L. artedi in Lake Erie, stated that first spawning is 
“probably at the end of the third summer.” The ciscoes of the inland lakes of 
southern Wisconsin spawn at the age of 3 years (Cahn 1927). Van Oosten (1929) 
found that in the Saginaw Bay herring only a few fish matured in the second year, 
and that the majority maturedun the third[and fourth years of life. Van Oosten’s 
data were based on the examination of individuals from the spawning run. In the 
Lake Ontario cisco Pritchard (1931) found a few females but no males mature at 
2 -{-years. He stated further that several individuals of both sexes were mature at 
3 + years, while spawning was general at 4 -{-years. Dymond (1933) found that in 
Hudson Bay the cisco does not mature “until the fourth and probably the fifth year.” 
The sex ratio expressed as the number of females per 100 males was determined 
by age groups for each of the four populations. These data are presented in table 49. 
Table 49. — Sex ratio according to age in each of the four populations 
[The ratio is expressed as the number of females per 100 males. The numbers of specimens are shown in parentheses. The age 
groups which were composed entirely of one sex are indicated by the sex symbols. The Clear Lake data were obtained by com- 
bining the 1931 and 1932 collections. The data for the remaining three lakes are based on the combination of the 1930 and 1931 
collections] 
Lake 
Age 
I 
II 
III 
IV 
V 
VI 
Trout 
100 (2) 
100 (26) 
110 (66) 
72 (69) 
162 (97) 
130 (472) 
160 (26) 
89 (102) 
204 (520) 
151 (361) 
126 (86) 
94 (95) 
354 (368) 
cf(2) 
111 (160) 
86 (39) 
1, 367 (88) 
1, 100 (12) 
Silver ... 
129 (133) 
82 (20) 
200 (24) 
100 (26) 
Clear 
Lake 
Age 
Average 
VII 
VIII 
IX 
X 
XI 
XII 
Trout 
9(4) 
400 (5) 
9(2) 
<? (2) 
9(D 
267 (1,101) 
137 (861) 
124 (496) 
104 (440) 
Silver 
9(1) 
194 (50) 
Clear.. 
210 (31) 
300 (4) 
9(3) 
9(D 
