YELLOW PERCH IN SAGINAW BAY 



371 



250r- 



JAN. FEB MAR APR. MAY JUNE JULY AtA SEPT OCT. NOV. DEC 

 MONTH 



Figure 4. — Average monthly commercial production of yellow perch in Saginaw Bay, 192&-55. 



9 other months constituted 25 percent of the 

 perch production, varying from 0.7 percent in 

 May to 5.6 percent in April. The take in late 

 spring and early summer would have been greater 

 had not closed seasons been in effect. The dates 

 of these seasons in various years have been : 

 1927-33, April 15-June 15; 1933-37, April 15- 

 May 15; 1937-47, April 15-June 1; 1947-56, 

 April 15-May 10. 



AGE COMPOSITION AND YEAR-CLASS 

 STRENGTH 



Annual and Seasonal Differences of Age Distribution 



The age composition of yellow perch caught 

 by commercial trap nets in Saginaw Bay in 

 May or early June varied considerably from year 

 to year (table 7; fig. 5). Because these samples 

 came from the spawning run, they probably 

 were biased by segregation on the basis of matu- 

 rity. Hile and Jobes (1942) held that during 

 this period the younger, immature fish were usu- 

 ally not highly represented. Nevertheless, sam- 

 ples collected in the same season throughout the 

 whole period of study (1943-55) will, despite 

 their bias, bring out annual changes of age dis- 

 tribution. Effects of gear selectivity likewise 

 were reduced by using only fish from trap nets. 



The dominant age varied between age group 

 III and age group V. Age group III dominated 



the catch in only 1 year (1951) and the V group 

 was dominant in 4 years (1945, 1948, 1949, and 

 1954). Age group IV dominated in the remain- 

 ing 6 years (1943, 1946, 1948, 1950, 1953, and 

 1955). In 2 years (1949 and 1954) the percent- 

 age representations of the two most plentiful age 

 groups (IV and V) were nearly equal (1949, 

 40.3 and 38.4 percent; 1954, 43.6 and 44.7 per- 

 cent). The representation of other age groups, 

 i. e., age groups II and VI-IX, during this 11- 

 year period was consistently less than 10 percent 

 except for the 1945 when age group VI formed 

 16.2 percent of the sample. In the combined 

 1943-55 collections age group IV constituted 48.6 

 percent of the total, followed by age group V 

 (29.9 percent) and age group III (15.9 percent). 

 The remaining age groups (II and VI-IX) to- 

 gether contributed only 5.6 percent. 



The year-to-year change in age composition of 

 spawning-run samples is reflected in fluctuations 

 of the average age. The oldest fish were caught 

 in 1945 (average age 5.1 years) and the youngest 

 in 1951 (3.8 years). The mean age was below 4 

 years in 1946 and 1947 also, but in the remaining 

 years ranged between 4.0 (1950) and 4.6 (1948). 

 The mean of the averages for the 11 spawning- 

 run samples was 4.3 years. 



Information on the seasonal fluctuation in age 

 composition of yellow perch from Saginaw Bay 



