YELLOW PERCH IN SAGINAW BAY 



409 



Nearly all the males were mature including 

 the smallest size captured (100 percent at 5.0- 

 5.4 inches; 96 to 99 percent at lengths of 5.5-7.4 

 inches). All males more than 7y 2 inches long 

 were mature. 



Females attain sexual maturity at a slightly 

 greater length than do males. No females were 

 mature at 5.0-5.4 inches and fewer than half 

 (44 percent) were mature at 5.5—5.9 inches. At 

 all greater lengths, however, the majority of the 

 females were mature. The 80-percent level was 

 reached at 7.0-7.4 inches and the 95-percent figure 

 passed at 8.0—8.4 inches. All females more than 

 9 inches long were mature. 



The evidence in table 54 on the small size of 

 Saginaw Bay yellow perch at first maturity 

 indicates that the protection of immature fish to 

 preserve a spawning stock needs little considera- 

 tion in the management of the fishery. The 

 present size limit of 8y 2 inches permits the cap- 

 ture of almost no immature fish and destruction 

 of nonspawners would be unimportant even at 

 7 inches. The double protection from the 8V2- 

 inch size limit and a closed season during spawn- 

 ing seems unnecessary. Indeed, under present 

 fishing conditions the imposition of either a size 

 limit or a closed season must be justified on eco- 

 nomic grounds. 



The size at first maturity of Saginaw Bay yel- 

 low perch in 1943-55 appears to be closely similar 

 to that in the same stock in 1929-30 and in 

 Green Bay. Hile and Jobes (1941) published 

 no details on the state of the gonads of the perch 

 in their Saginaw Bay samples, but their com- 

 ment that 96 percent of their specimens were 

 mature and the published length frequencies give 

 strong evidence of maturity at small size. For 

 Green Bay perch Hile and Jobes (1942) stated 

 that males were predominantly mature down to 

 a length of 5 inches. A majority of females 

 were immature at lengths below 7 inches but 59 

 percent were mature at 7— 7y 2 inches and all were 

 mature at lengths above 7y 2 inches. 



Yellow perch mature at a greater length in Lake 

 Erie than in Saginaw Bay and Green Bay. The 

 50-percent level of maturity is first exceeded by 

 the males in Lake Erie at 6i/ 2 — 7 inches and by 

 the females at 8y 2 -9 inches (Jobes 1952). 



Sex Ratio 



The present study of the sex composition of 

 Saginaw Bay yellow-perch population has served 



principally to confirm the findings of earlier in- 

 vestigators concerning the extreme variability of 

 the sex ratio in samples of the species (Schne- 

 berger 1935 ; Weller 1938 ; Eschmeyer 1937, 1938 ; 

 Hile and Jobes 1941, 1942; Jobes 1952; Aim 

 1946, European perch). Jobes (1952) showed 

 that the sex ratio of Lake Erie yellow perch 

 varied erratically even in day-to-day collections. 

 He concluded that the best estimate of the sex 

 ratio in the population could be obtained from 

 the unweighted means of the percentages of males 

 and females, determined for several individual 

 samples. 



Eschmeyer (1938) attributed this wide sam- 

 ple-to-sample fluctuation in the sex ratio to a 

 persistent segregation of the sexes in nonspawn- 

 ing fish and during the spawning season. He 

 based his conclusion on the stomach contents of 

 fish that had been killed in the poisoning of an 

 entire population. Females had consumed items 

 characteristic of the surface and of shallow water, 

 whereas males had eaten deep-water forms. 



Sex ratio of individual samples 



The data on sex ratio of Saginaw Bay yellow 

 perch from the spawning runs in 1943-55 (right 

 column, table 55) show pronounced year-to-year 

 variability. The percentage of males varied from 

 26 percent in 1945 to 87 percent in 1954. In 4 

 years (1943, 1946, 1947, 1953) the sexes were 

 nearly equally represented. For all the collec- 

 tions combined, the males were more abundant 

 than the females (62 percent males). 



Wide fluctuation in the sex composition was 

 observed not only from year to year but also in 

 collections of the same year (table 56). The 

 males were most plentiful at the beginning and 

 at the end of spawning season (April 18, 70 per- 

 cent; June 7, 65 percent). On the other hand, 

 females predominated strongly in the collections 

 of June 22 (33 percent males) and October 19 

 (30 percent males). Males and females were 

 represented equally in the remaining sample 

 (May 18). 



A high percentage of males in spawning-run 

 samples has been observed commonly and among 

 many species of fish. Different explanations of 

 the phenomenon have been offered. Numerous 

 investigators believe that males ripen sooner, 

 move to the spawning grounds earlier, and re- 

 main there longer than do females. Deason and 

 Hile (1947) showed that this explanation did 



