Invariably, these precocious fish arrived at the 

 spawning site in July, near the end of the spawn- 

 ing season. They were not the largest of their 

 age group, whose length range extended to 254 

 mm. at this time, but were generally above the 

 average length. They obviously represented only 

 a fraction of their group, but the exact percentage 

 could not be determined because segregation ac- 

 cording to maturity is great during the spawning 

 season. 



Most spawners were in their third year of life 

 (II group), but not all shad of this age group 

 spawned. The average length of the June 1954 

 II-group females that would have spawned (29 

 cm.) was 1 cm. greater than that of the shad 



Table 15. — Sex ratios for gizzard shad for which both sex and 



age were determined monthly 

 (These shad were captured in the vicinity ot the Bass islands in 1952-55] 



which would not have spawned during the current 

 year (28 cm.). Although the percentage of the 

 female shad that matured during their third year 

 of life could not be determined because of the 

 segregation according to maturity, observations 

 on gonads of shad captured throughout the year 

 indicated that at least SO percent of them became 

 mature at this age in western Lake Erie. Only 

 rarely were female shad older than the II-group 

 immature. With few exceptions, the II-group 

 male shad had well-developed testes. Since, how- 

 ever, I was unable to determine maturity in the 

 absence of flowing milt, I could not distinguish 

 a spent individual from one which had not 

 spawned — in fact, could not judge from the state 

 of the testes in any month the percentage of 

 mature males of any age group. 



Sex Ratio 



The gizzard shad captured in the vicinity of 

 the Bass Islands in 1952-55 for which sex could 

 be determined were combined to show trends of 

 the sex ratio by month and by age (table 15). 



Only limited seasonal trends are apparent from 

 the data on sex ratio; the month-to-month fluctua- 

 tions were decidedly irregular. 



Among the 10 months in which the total sam- 

 ples exceeded 250 fish, July stands apart because 

 of the small percentage of males (37.0 percent). 

 Among the other 9 months, this percentage ranged 

 between 41.9 (May) and 54.9 (February). The 

 percentage for all 12 months was 47.6. 



The percentage of males varied little among the 

 four younger age groups (45.6-49.7 percent males) 

 in the combined sample for all months, but males 

 became less numerous at the higher ages (38.6 

 percent in age groups IV-VI, combined). 



Information on the percentage of males in 

 samples from the shallow waters of Fishery Bay 

 and the deeper waters of the lake gives no indica- 

 tion of segregation of the sexes within the lake 

 except for age groups II and III (shad of spawning 

 age) during June. The records for that month 

 (table 16) suggest that males are relatively more 

 plentiful at the spawning site than in the deeper 

 water. The data on sex ratio on the spawning site 

 during the spawning season are undoubtedly biased 

 in favor of the males since their greater activity 

 increases the likelihood of capture by the sta- 

 tionary fishing gear. This bias, however, does not 

 account entirely for the large percentage of mules 



408 



U.S. FISH AND WILDLIFE SERVICE 



