The stomach contents of adult gizzard shad 

 exhibited no appreciable differences among indi- 

 vidual shad of a group collected in a locality at 

 the same time. Evidence was lacking for any 

 selection of food within the size range of material 

 they swallow. There were, however, local and 

 seasonal differences related, undoubtedly, to the 

 abundance of the various forms in different places 

 and at different times. As a result of these ob- 

 servations, examination of stomachs of individual 

 fish was soon discontinued and the stomach con- 

 tents of several fish of a collection were combined. 



The feeding habits of gizzard shad were well 

 summarized by Tiffany (1920) who indicated 

 them to be a living tow net. No attempt was 

 made in the present study either to obtain the 

 percentage of each item ingested or to enumerate 

 every organism eaten by the shad at one time or 

 another. In table 24 are listed only major groups 

 of materials found in shad during various months. 

 The table does not identify the months in which 

 the gut contained the most food; in general, the 

 quantity was more plentiful when the diet con- 

 sisted of a great variety of food in June through 

 November. 



Velasquez (1939) cultured algae taken from 

 various parts of the shad gut. As a result either 

 of rapid transit through the gut, or absence of 

 certain enzymes, some algae or certain algae 

 apparently are not utilized as food. 



SUMMARY 



This study of the life history of the gizzard shad 

 was based on records of the length, weight, and 

 age of almost 24,000 specimens taken in western 

 Lake Erie in 1952-55. Approximate numbers of 

 fish employed in other phases of the study were: 

 calculation of growth from scale measurements, 

 700; seasonal fluctuations of gonad weight, 700; 

 sex ratio and maturity, almost all fish over 120 

 mm. long; feeding habits, 200; seasonal develop- 

 ment of ovaries, 150; and fecundity, 13. 



The fish were captured by means of dip nets, 

 "Common Sense" seines, hag seines, push seine, 

 gill nets of various mesh sizes, regulation commer- 

 cial trap nets, and by electric shock, dynamite, and 

 rotenone. Fish older than the O-group were cap- 

 tured mostly by the gill nets and trap nets. Most 

 fish were captured within one-half of a mile of 

 the Bass Islands. 



The scales of the gizzard shad are described 

 briefly. Two types of annuli are present — a 

 narrow clear-cut line of demarcation and a wider, 

 more evident one. The first annulus is always 

 of the former variety; the second and succeeding 

 ones (with few exceptions) are of the latter variety. 

 The wider, obvious annulus may be a combination 

 of an annulus and a spawning check, whde the 

 narrow variety is strictly an annulus. 



The time of annulus formation varied with age 

 and sex. Some of the I-group shad began to form 

 the new annulus in May, and all had it by the end 

 of the first quarter of June. Annulus formation 

 of older shad began in June and was completed by 

 mid-July. Females seem to have formed their 

 new annulus about a week earlier than the males. 

 Spawning of these older females occurred while 

 annulus formation was in progress — some fish 

 spawned before the appearance of the new 

 annulus — some after its appearance. Although 

 prespawning development of the gonads was 

 thought to affect the physical appearance of the 

 annulus, the spawning act appeared to have no 

 effect on the time of its appearance. Evidence 

 was given that the annulus is a true year mark. 



The body-scale relation was a straight line with 

 an intercept of 22.1 mm. on the axis of standard 

 length. 



Calculated lengths showed good agreement with 

 empirical lengths of shad captured between the 

 first of the year and the time of annulus forma- 

 tion — except for the I group. The greater average 

 length of I-group fish at capture can be attributed 

 to gear selectivity. 



Sampling problems made the determination of 

 age composition difficult. The young gizzard 

 shad were found in shallow water, the older in 

 deeper water, and the very oldest were captured 

 only during the spawning season. Shad captured 

 in the open lake during fall probably gave the best 

 available estimate of the relative strength of 

 younger age groups. Those captured during the 

 spawning season were most nearly representative 

 of the age composition among the older shad. On 

 these assumptions the following survival from an 

 original 100,000 I-group fish were computed: 

 [I-group, 5,534; Ill-group, 435; IV-group, 63; 

 V-group, 11: and VT-group, 6. 



The 1952 year class was one of more than usual 

 abundance. In 1953, as I-group they constituted 



422 



U.S. FISH AND WILDLIFE SERVICK 



