spawning area of shad within the confines of the Delta in 19h8. Produc- 

 tion of young shad from this source was continuous, with larval specimens 

 taken as late as October. 



The growth of larval shad was rapid. Those in the southern part 

 of the Delta were of greater average length than those from Sacramento 

 and Mokelumne River sources. However, the average length of the larvae 

 from all stations for the 9th and 10th towing cycles, June 16 to July 12, 

 was less than 20mm (0.8 inch). The peak of abundance occurred in the 

 11th towing cycle. Most larvae had completed transformation to the 

 juvenile form by the end of the 12th towing cycle, July 20-August 3, and 

 had attained a mean length of 33mm (1.3 inches). The growth of juvenile 

 shad was also very rapid. Their mean length was h!?mm by the middle of 

 August, and 3>7mm by the end of August. By the end of September, in the 

 16th towing cycle, the young shad had attained a mean length of 70mm. A 

 few averaging 75mm in length were taken in November, the 18th towing 

 cycle. 



Evidence of the seaward movement of young shad was noted from the 

 results of the succeeding towing cycles (Figure 8) . Larval shad were 

 flushed from the upper Sacramento River spawning grounds by river run- 

 off toward Suisun Bay, with significant numbers diverted into the cen- 

 tral San Joaquin Delta via Georgiana Slough. The peak of the Sacramento 

 migration occurred during the 11th cycle, July 12-20, followed by a 

 secondary peak in the 13th cycle, August h-17. Juvenile shad from 

 San Joaquin River above the Delta and from the southern section were 

 slower in their downstream movement, peaking in the 12th cycle. These 

 fish spread out into the central Delta area Large numbers of shad 

 persisted in the lower Mokelumne River through the 12th cycle, July 20- 

 August 3. However, a gradual movement from the Mokelumne into the 

 central San Joaquin Delta was evident in the 11th and 12th cycles. Emi- 

 gration from the Mokelumne was definite by the ena of the 13th cycle, 

 and was reflected in the larger catches from stations 15> and 17 in the 

 lower San Joaquin River. Dispersal of the Mokelumne shad through the 

 central Delta area was evident in cycles 13 and lit. The tendency of some 

 of the shad to remain within Delta waters was indicated by catches of 

 the larger size shad at a majority of the stations as late as the last 

 week of October, with even a few taken in November. 



The study of shad distribution in Delta waters in 191+9 was con- 

 ducted in the same manner as in the previous year. However, weekly 



sampling at the tow-net stations gave a more representative distribu- 

 tion pattern of the larval and juvenile shad in the Delta. Relocation 

 of stations 18 and 19 (Figure 1) on the South and North Forks of Moke- 

 lumne River was helpful in evaluating the importance of these waters as 

 shad producers. In 19^9 the total catch of the early life stages of 

 shad with the five-foot tow net was 22,U6l specimens. Of this catch a 

 random sample of 8,U05 individuals was measured for studies in growth 

 rate. Data for the tow-net stations are given in Appendix Table 16 and 

 are further summarized in Appendix Table 2. The distribution of shad as 

 determined from tow-net samples is presented graphically in Figure 9. 



33 



