The first catches of shad larvae were made in plankton-net hauls 

 in the 13th cycle (April 18-21, 19U9) at station 8 in the San Joaquin 

 River and at station 21 in the Worth Fork of Mokelumne River „ There™ 

 after, shad larvae were taken occasionally in plankton-net hauls, but 

 never in significant numbers . Catches of advanced forms of larval 

 and juvenile shad with the standard five-foot tow net were first made 

 in the 18th cycle (May 2ii~26, l°USj in the North Fork of Mokelumne 

 River and in Old River near the approach canal of the Tracy Pumping 

 Plant . By the 20th cycle (June 6-9, 19U9) shad larvae were taken in 

 Georgiana Slough, Sacramento River below Rio Vista, in the forks of 

 Mokelumne River, and in several stations in the southern Delta, A wide 

 dispersion. of larval and juvenile shad was recorded in the 21st cycle 

 when 21 of the 26 stations yielded large numbers of fish. From then on 

 the total catch for each cycle increased rapidly until the peak of 

 abundance occurred in the 23rd cycle (June 27-30, 19^9) . Although many 

 of thestations continued to yield larval forms, particularly stations in 

 Mokelumne River, the growth rate was rapid with the average length ex- 

 ceeding the 25-28mm measurement considered to be the length at which 

 transformation occurs (Leim 192U) . The distribution of immature shad in 

 the succeeding cycles remained relatively constant to July 22, Mokelumne 

 River continued to be the most important source of shad production, with 

 the Sacramento River stations also yielding significant catches. The 

 rapid growth continued so that by the 26th cycle the mean length of the 

 measured catches was 3U.9 (1.5 inches). 



Catches of larvae and juveniles became progressively smaller after 

 the 26th cycle, with the central portion of the Delta continuing to yield 

 the principle catches. This tendency prevailed until the termination of 

 field activities on September 22, at which time it was apparent that the 

 results of further sampling would have paralleled those of I9I4.8. 



The charts clearly show that larval and juvenile shad were always 

 concentrated in areas which will be within the influence of flows to 

 the Tracy Pumping Plant, 



WATER FLOW IN RELATION TO FISH POPULATIONS 



The preceding sections have dealt separately with the distribution 

 and occurrence of juvenile king salmon, striped bass, and shad in the 

 Sacramento-San Joaquin River Delta, The charts illustrating this infor- 

 mation for each species have shown their relative abundance and distribu- 

 tion in relation to the various channels that form the Delta, They have 

 also portrayed abundance in relation to time and demonstrated an overlap 

 of all species. Overlapping of species is more clearly seen in Figure 10 

 where the juveniles of all species are shown to be present in considerable 

 numbers in the months of June and July, This figure also demonstrates 

 that fingerling salmon are present in Delta waters as early as February 

 and remain there until the latter part of July. 



35 



