368 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



fish with one annulus belong to age group I, 

 those with two annuli to age group II, * * *. 

 (Young-of-the-year are assigned to age group 0.) 

 Hile (1948) recommended for convenience and 

 for the consistency in the relation of year of 

 origin, year of capture, and age, that each fish 

 be considered to pass into the next higher age 

 group on January 1. Under this convention a 

 "virtual" annulus is credited at the edge of the 

 scale from January 1 until the new annulus is 

 actually formed in spring or early summer. Year 

 classes, identified by the year of hatching, thus 

 can be determined by subtracting the age from 

 the year of capture; for example, a fish of age 

 group IV captured in 1955 belongs to the 1951 

 year class. 



COMMERCIAL FISHERY FOR YELLOW 

 PERCH 



General Trends of the Fishery, 1891-1955 



Statistics of the production of yellow perch in 

 Saginaw Bay were available for the years 1891- 

 1908 and 1916-55 (table 2 and fig. 2). Although 

 production always has varied widely, almost 

 erratically, two intervals (1891-1916 and 1917- 

 55) can be established within which these varia- 

 tions showed no definite trend. The first period 

 (1891-1916) was one of high production. The 

 annual catch varied from 3,379,200 pounds in 

 1901 to 1,085,788 pounds in 1908. The average 

 yield for the whole period (19 years) was 1,961,309 

 pounds. On the other hand, in the second period 

 (1917-55), the commercial catch was far below 

 that of the early years. The annual production 

 was above a million pounds in only two years 

 (1919 and 1936) and the average catch for the 

 whole period (499,938 pounds) was 74 percent 

 below that of the early interval. This percent- 

 age did not differ much from 72 percent re- 

 corded by Hile and Jobes (1941) for the 1917-38 

 period. Since 1938 (1939-55) the commercial 

 catch has been below 500,000 pounds except in 

 1943, 1944, and 1945. The highest yield was in 

 1943 (883,087 pounds) and the lowest was 

 reached in 1947 (250,570 pounds). 



Hile and Jobes (1941) believed the low pro- 

 duction of 1917-38 was due to a less dense yellow 

 perch population in Saginaw Bay that had re- 

 sulted from overfishing. Data for recent years 

 (the relatively small catches of 1939-55) suggest 



Table 2. — Annual commercial production of Saginaw Bay 

 yellow perch in 1891-1908 and 1916-55 



that the yellow perch recently might have become 

 even scarcer and hence need protection even 

 more than in 1938 and earlier. However, the 

 records of fishing pressure and availability or 

 abundance (table 3) show that after 1938 (1939- 

 55), fluctuations in the abundance of yellow perch 

 (fig. 3) were irregular but with a definite upward 

 trend. 3 On the other hand, fishing intensity was 

 declining though with some irregularities. The 

 decrease of intensity was great enough that the 



Table 3. — Abundance, production, and fishing intensity 

 for Saginaw Bay yellow perch fishery in 1929-55 



3 Indices of abundance given in table 3 were derived from data 

 on tbe catch per unit of effort (£able 4) by the method described 

 by Hile (1937) ; the method of computing the intensity index was 

 described by Hile and Jobes (1941). 



