388 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Table 27. — Calculated total length at the end of the different years of life for female yellow perch collected during the spawning 



seasons of 1949-55 



Most of the calculated lengths of age groups 

 VII-IX of the females, on the other hand, were 

 greater than the corresponding calculated lengths 

 of younger age groups. That these discrepancies 

 can be attributed to erroneous interpretation of 

 the difficult scales of old fish seems unlikely since 

 the trend toward higher calculated lengths among 

 the older perch is present in the earlier as well 

 as in the later years of life. Ordinarily the first 

 3 or 4 annuli are easy to locate and measure even 

 on the scales of old fish. Inasmuch as age groups 

 VII-IX were represented by only 10 fish it can 

 hardly be concluded that the survivors to ad- 

 vanced ages are regularly the more rapidly grow- 

 ing individuals, but the possibility of such a 

 selective survival should not be ignored. 



The discrepancies shown in tables 26 and 27, 

 for yellow perch other than the older females, 

 exhibit a different pattern from that of "Lee's 

 phenomenon of apparent decrease in growth rate" 

 as defined by that author (Lee 1920). In Lee's 

 phenomenon the discrepancies among calculated 

 lengths are greatest in the early years of life and 

 become less and less in later years. In the Sagi- 

 naw Bay perch, on the contrary, the disagree- 

 ments affect the later years of life most severely. 

 A similar situation has been reported earlier for 

 Saginaw Bay by Hile and Jobes (1941) and also 

 for perch of Lake Erie (Jobes 1952) and Green 

 Bay (Hile and Jobes 1942) and for certain spe- 

 cies of deep-water ciscoes (Jobes 1949a, 1949b, 

 and 1943; Deason and Hile 1947). 



A change in calculated lengths occurred also 

 between samples of the same age group caught 



in spring and fall (tables 28 and 29). Among 

 males the disagreements were generally smaller 

 between the calculated lengths of any age group 

 caught in the fall and the next higher age group 

 caught in the spring than were the differences 



Table 28. — Calculated lengths of spring and fall samples 

 of 3 age groups of male yellow perch, 1955 



Age group and time of 

 capture 



III 



Spring 



Fall 



IV 



Spring 



Fall 



V 



Spring 



Fall 



Num- 

 ber 

 of 

 fish 



179 

 58 



149 

 12 



Length (inches) at end of year 



2.9 

 2.7 



2.7 

 2.7 



2.6 

 2.7 



4.8 

 4.2 



4.1 

 4.1 



3.9 

 4.0 



 6.0 

 5.3 



5.4 

 5.2 



5. 1 

 4.8 



6.1 



5.8 



17.0 



'7.1 

 6.6 



1 Size at capture. 



1 Mze at capture. 



