YELLOW PERCH OF L.\KE ERIE 



261 



The reasons for the apparent segregation of the 

 sexes of the Lake Eric yellow perch are largely un- 

 known. The segregation during April and May 

 perhaps was due to the spawning-season habits of 

 the species. A segregation associated with se.x 

 differences in feeding habits during the summer 

 months, such as was found by Eschmeycr (1938), 

 may occur. Materials for study of the food of 

 the Lake Erie perch were not available. Another 

 possible factor in the fluctuating sex ratios during 

 the summer is age. The females tend to increase 

 in relative abundance with advancing age; con- 

 sequently, variation in the age composition of the 

 samples would contribute to an apparent segrega- 

 tion of the sexes. However, this explanation can 

 account for only part of the variation in the sex 

 ratio since the ratios varied \\idely in samples of 

 fish of the same age but taken on different days of 

 the same month (table 38). 



Age determinations of certain of the above 

 materials permit the examination of the relation 

 between the proportional representation of the 

 sexes and age. Table 38 shows the sex ratio of 

 Lake Erie yellow perch in a number of samples, 

 expressed as the percentage of males in the total, 

 by age group. Because of the daily fluctuations 



Table 38. — Percentage of male Lake Erie yellow perch by 

 age grorips, according to date of capture 



[Total numbor of sppcimpns In parontheses] 



in sex ratio the data have been presented for dailj' 

 catches as well as bj' the month and for all months 

 combined. In spite of certain exceptions, it may 

 be said that there was a progressive decrease in 

 the proportion of males as the age increased. It 

 is apparent that either the relative abundance of 

 males in the stock was progressivelj^ less with each 

 yearly increase in age, or that the females were 

 progressively more available to the fishery. 



Sex differences in the age of entry into the 

 fishery can produce an "apparent" change in the 

 sex ratio with increase m age. The earlier attain- 

 ment of maturity by the males, together with their 

 apparent tendency to remain on the spawning 

 grounds longer than the females, doubtless ac- 

 counted for the great preponderance of males in 

 age groups I and II and their abundance in age 

 gi-oup III of the spawning-run (April 1932) collec- 

 tion. Consequently, the decrease in relative 

 abundance of males \ni\\ increase in age in that 

 collection caiuiot be accepted as descriptive of the 

 general population. Significance must be as 

 cribed, however, to the fact that a similar, if less 

 pronounced, change in the sex ratio occm-red in the 

 collections of other months when there is no 

 reason to believe that a segregation on the basis 

 of maturity existed. In a majority of the samples 

 taken in months other than April the males ex- 

 hibited a tendency to decrease in relative abun- 

 dance with increase in age. It may be concluded 

 that this tendency of the males is a real and not 

 an apparent characteristic of the Lake Erie 

 yellow perch. 



The acceptance of a shifting sex ratio with age 

 as characteristic of the Lake Erie yellow perch 

 population carried with it the assumption of a 

 differential mortality of the sexes. This differ- 

 ence in death rate may have its origin in a selective 

 destruction in the fishery or it may depend on sex 

 differences in the natural mortality rate. 



It would appear that a differential destruction 

 of the sexes by the fishery is the most plausible 

 explanation of the changes in sex ratio Avith age 

 of the Lake Erie yellow perch. The males 

 mature at a j-ounger age, and consequently, are 

 taken by the nets during the spawning season 

 earlier in life than are the females. Furthermore, 

 the apparent tendcncj' for the males to arrive 

 earlier and stay longer than the females on the 

 spawning grounds increases the chances of capture 

 for any particular male, and presumably would 



