of June in the Fishery Bay samples. Thereafter, 

 all samples from both bay and lake showed in- 

 creasing percentages of spent shad during June. 

 In July, this trend persisted among the lake 

 samples, but in the bay samples both spawning 

 and spent fish were absent after the first quarter 

 and only three nonspawning ones were captured. 

 The available data indicate that the gizzard shad 

 in western Lake Erie spawn during June and early 

 July; the greatest percentage of them spawn in 

 the second quarter of June. 



Records of the average ovary weight as a 

 percentage of the fish weight, for II-group and 

 older female shad in 1954-55 (table 21), indicate 

 that the ovary makes little increase in weight 

 from the time the fish are spent until the following 

 April. During that month, feeding increases (this 

 is the first time in winter or spring during which 

 recognizable food has been found in the shad's 

 gut — -table 24), but the fish weight decreases 

 (table 9). Consequently, the combination of a 

 little ovarian growth and loss of fish weight 

 results in a rise in the ovary-weight/fish-weight 

 ratio. This ratio is highest either in the last 

 quarter of May, for which I have no samples, or 

 the first quarter of June. In this period, more 

 fish are just ready to spawn and fewer are spawning 

 or are spent than at any subsequent period. Then, 

 as more fish become partly or completely spent, 

 the average ratio drops lower. The drop in 

 June is steady, and in the last quarter of that 

 month the ovary weight as a percentage of body 

 weight is again at about the April level. I have 

 no ovary weights for July, August, and September. 

 However, since some shad are still spawning in 



Table 21. — The percentage of fish in the categories "not 

 spawning", "spawning", and "spent", and the ovary 

 weight as a percentage of the fish weight for I I-group and 

 older female gizzard shad, Lake Erie, 1954-55 



Period 



Oct _. 



Nov 



Dec 



Jan — 



Feb 



March 



Apr. .. 

 May 1-8..-. 

 May 9-15. . . 

 May 16-23 i 

 June 1 8 

 Iir i' y-15. . 

 .Tune 16-23. 

 June 24-30. 



Ovary/fish 

 weight 



Percent 

 1.1 

 .9 

 1.5 

 1.1 

 1.8 

 1.5 

 2.4 

 3.8 

 4.2 

 4.3 

 9.9 

 8.5 

 5.3 

 2.5 



i No samples May 24-31. 



416 



July and follicular remains were yet to be absorbed, 

 I suspect the low percentage of winter samples 

 is not reached earlier than the last of July. 



The mature I-group gizzard shad spawn later 

 than older fish. Ova of three fish captured 

 during the 1954 spawning season (June 28, July 6, 

 and July 8) were nearly ripe (fig. 10). These 

 fish probably would have spawned in late July 

 or early August, or else the ova would have been 

 resorbed. 



The eggs of the II-group fish which have been 

 in the making for \% to 2 years — much longer 

 than those of older fish — might be expected to be 

 spawned earlier than those of older fish. Infor- 

 mation on the older shad is too scanty, however, 

 to permit study of this possibility. 



The weight of the fish appeared to have no 

 effect on the time of its spawning. 



I tried two methods to determine the time of 

 spawning within a 24-hour period. In one, a gill 

 net was set on the previously mentioned spawning 

 bar in the afternoon, lifted at midnight, reset 

 immediately, lifted in the morning, reset again, 

 and lifted in the afternoon. The numbers of 

 shad of each sex were tabulated for each period. 

 In the other method, concrete slabs with a surface 

 area of 1 square foot were lowered to the bottom 

 at the spawning site and examined for shad eggs 

 three times daily, when the gill net was lifted. 



Studies by the two procedures covered only 3 

 days, June 17-19, 1954; in 1955, the net method 

 alone was employed (June 2-11). The gizzard 

 shad spawned most actively in the evening and 

 early night in 1954 and at night in 1955 (table 22) ; 

 spawning was least in the daytime in both years. 

 I have not seen shad spawning during the day- 

 time, but have seen them milling actively, fre- 

 quently breaking surface, when I lifted the net 

 at midnight, especially in moonlight. 



The individuals participating in' the spawning 

 change continually during the season, but a female 

 does not deposit all her eggs during one nightly 

 visit to the bar. Although the percentage of eggs 

 remaining in the ovaries varies among individual 

 fish throughout most of the spawning season, 

 numerous partially spent fish with a substantial 

 percentage of eggs still in the ovary are taken 

 early in the season. Almost none carry large 

 percentages of their eggs toward the close of the 

 season. The state of development of the "nearly 

 mature" ova and the free ones in the ovaries of 



U.S. FISH AND WILDLIFE SERVICE 



