372 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



20 



20 



60 



40 



20 



ui 70 

 a. 



60 



40 



20 



40 



20 



50r 



1945 



1947 



1948 



1949 



U 01 IV V VI W 



AGE GROUP 



u in iv wivnvuix 



AGE GROUP 



Figure 5. — Age composition 

 tions of Saginaw Bay 



of the spawning-run collec- 

 yellow perch, 1943-55. 



is limited to 1955 when collections were made on 

 April 18, May 18, June 7, June 22, and Octo- 

 ber 19 (table 8; fig. 6). The data indicate no 

 clear-cut seasonal change of age composition and 

 average age. 4 The average age decreased from 

 4.8 on April 18 to 4.4 on May 18 and to 3.8 on 

 June 7, then increased to 4.3 on June 22. On 

 October 19, the average age decreased again to 

 3.7. This change in average age was accompanied 

 by a shift in the dominance of age groups. Age 

 group V was strongest on April 18 (45.6 per- 



* Records in table 8 are for the sexes combined since males and 

 females exhibited similar seasonal trends. 



Figure 6. — Age composition of Saginaw Bay yellow perch 

 on different dates in 1955. 



cent), whereas age group IV dominated the col- 

 lections of May 18, June 7, June 22, and October 

 19 (48.4, 47.2, 51.9, and 53.1 percent, respec- 

 tively). Age group III composed as much as 

 32.6 and 23.8 percent, of June 7 and October 19 

 samples, and as little as 2.6 percent (April 18). 

 The representation of the VI group ranged from 

 13.5 percent (April 18) to 1.2 percent (June 7). 

 Members of age groups II and VII were scarce 

 or lacking in all samples except on October 19 

 when age group II constituted 11.1 percent of 

 the sample. 



In comparing Saginaw Bay perch with other 

 yellow perch populations, consideration must be 

 given only to those fish caught in similar seasons, 

 since age composition varies within the year. A 

 comparison of Saginaw Bay perch during the 

 present period of study (April, May, and June 

 collections) with those of 1929-30 (spring and 

 early summer) discloses greater age in more re- 

 cent years (table 9). In 1929-30 age groups III 

 and IV were best represented; each made up 

 about 39 percent of the total collection. During 

 the 1943-55 period, age groups IV and V consti- 

 tuted 48.6 and 29.9 percent, respectively, of the 



