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FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 55. — Sex composition of Saginaw Bay yellow perch in spawning-run samples of 1948-55, expressed as percentage 



of males 



i The unweighted mean for the collections is 58. 



Table 56. — Sex composition of Saginaw Bay yellow perch in different seasons of 1955, expressed as percentage of males 



[Number of fish in parentheses, males at left, females at right] 



not hold for their data on the sex ratio of kiyi 

 (Coregonus [Leucichthys] kiyi) and suggested 

 that the great activity of males during spawning 

 led to their capture in numbers out of proportion 

 to their true abundance. Possibly both the actual 

 abundance and differential activity affect the 

 estimates of the sex ratio of spawning-run sam- 

 ples of perch. 



Change of sex ratio with increase in age 



The tendency toward a decrease in the percent- 

 age of males with advancing age has been re- 

 peatedly shown for many species. Hile (1936) 

 who reviewed the subject of change of the sex 

 ratio with age concluded with the suggestion 

 that this condition might be characteristic among 

 fish. A decrease in the percentage of males with 

 increase of age has been observed also in a num- 

 ber of yellow perch populations (Schneberger 



1935; Weller 1938; Hile and Jobes 1941, 1942; 

 Jobes 1952). Exceptions to this trend were re- 

 corded, however, by Eschmeyer (1937 and 1938) 

 and by Aim (1946) for populations of stunted 

 perch. Thus the possibility suggests itself that 

 the change in growth rate of Saginaw Bay yel- 

 low perch from 1929-30 to 1943-55 may be asso- 

 ciated with a reversal in the change of the sex 

 ratio with age. In the earlier years males grew 

 scarcer with increasing age whereas in most of 

 the 1943-55 samples (tables 55 and 56) the per- 

 centage of males increased with age (oldest age 

 groups excepted). 



In all of the 1943-55 samples, except for the 

 spawning-run collections of 1943 and 1945 and 

 the sample of June 22, 1955, the males became 

 more plentiful with increase of age. This trend 

 toward increase was so strong in some years 

 (1948, 1950, 1954) that fish in age group VI 



