Shad ( Alosa sapidissima ) 



Observations of the migration of adult shad in the Delta were 

 limited. The period of migration was established indirectly from the 

 catch of the commercial fishery. From this source, it was determined 

 that the fish entered the Delta on their spawning migration in early 

 spring, usually in March, and reached the peak of abundance in May. 

 Adults were observed in Sacramento River, Georgiana Slough, Mokelumne 

 River, San Joaquin River and its distributaries below Mossdale during the 

 spring months. During the month of June, 19h9 , large numbers of shad were 

 seen in these waters in dead or dying condition. 



Because of the nature of shad spawning activity and the character 

 of the eggs, observations on spawning and recovery of eggs were not 

 successfully accomplished with the collecting methods used. Consider- 

 able evidence substantiating the occurrence of spawning in the Delta 

 was obtained from sampling larval shad at the established tow-net sta- 

 tions. The study of the early life stages of shad and their distribu- 

 tion in the Delta was carried on concurrently with that of salmon and 

 striped bass. 



The introduction in I9I18 of the tow-net method of sampling selected 

 stations in the Delta made it possible to determine certain facts about 

 the spawning distribution of shad and the relative abundance and dis- 

 persion of larval and post-larval forms. During 19U8 a total of 

 6,606 larval and juvenile shad were collected in standard tow-net hauls 

 and a random sample of 3>908 individuals was measured for growth rate 

 studies. Data for each station are given in Appendix Table \$ s and 

 are further summarized in Appendix Table 1. Distribution and abundance 

 as determined from the sampling is illustrated graphically in Figure 8. 



The first evidence to indicate that shad reproduction was well 

 under way was collected during the 9th cycle, June l6-July 2, I9I18. 

 Larval shad were initially taken June 30th at towing stations located 

 in Sacramento and Mokelumne Rivers. Young shad were taken in increas- 

 ing numbers at these stations through July 20, the 11th towing cycle, 

 with an extraordinary increase in catch occurring in the North and South 

 Forks of the Mokelumne River. This large increment of young shad from 

 the Mokelumne extended through four cycles (10-13) , July 2 to August 

 17, and surpassed catch records from all other stations. The stations 

 in the central and southern delta also yielded significant catches of 

 post-larval shad. Tow-netting results from the stations in the Sacra- 

 mento River and Georgiana Slough indicated that considerable spawning 

 occurred in the Sacramento drainage above the Delta. Young shad entered 

 the Delta from Sacramento River from the first of July to the end 

 of October. Production of juvenile shad from the southern part of the 

 Delta and San Joaquin River above the Delta extended from July 2 to 

 October 23 with the peak yield from this area occurring in the 12th 

 towing cycle. However, it did not approach the magnitude of the catches 

 from Mokelumne and Sacramento Rivers. Mokelumne River was the major 



31 



