Striped bass and shad spawn in Delta waters in the spring, and the 

 resultant eggs and larvae are found throughout that area with notable 

 concentrations in its central portion. The juveniles of these species 

 remain in considerable numbers in Delta waters much longer than the 

 salmon. Collections of juvenile striped bass and shad were regularly 

 made through September, and shad were taken as late as November. Hook 

 and line fishing and exploratory tows proved the presence of juvenile 

 shad and striped bass in quantity in all other months of the year„ 



The egg, larval, and juvenile stages are particularly vulnerable 

 to the actions of the various components of their complex environment, 

 especially that of flow. The inability of eggs and larval fish to resist 

 current is a matter of common knowledge, and is a pertinent consideration 

 in this situation. Salmon juveniles and the juveniles of striped bass 

 and shad, because of their larger size, have greater power to resist 

 currents, and would not be affected to the same extent as larval forms of 

 striped bass and shad. Since shad eggs are demersal, currents dc not 

 affect them to the same degree as they do the pelagic striped bass eggs. 



The evidence obtained in this investigation seems conclusive that 

 the Delta provides excellent spawning and nursery grounds for the species 

 of fish emphasized in this discussion. It also demonstrates that the 

 various fresh-water phases of their life histories occupy the entire 

 twelve months of the year in Delta waters . This is particularly true with 

 striped bass and shad. 



Termination of the study at approximately the halfway mark pre- 

 vented intensive investigation into the problem of the distribution of 

 fish in relation to flow. However, sufficient evidence has been 

 gathered on this problem to indicate strongly that flow is the most 

 important controlling factor in the distribution of juvenile fishes in 

 the channels of the Delta. Evidence of primary importance was obtained 

 in 19U8 as a result of fishing fyke nets in Georgiana Slough and in 

 Sacramento River below Isleton during the peak of the spring seaward 

 migration of juvenile salmon. Georgiana Slough diverts Sacramento River 

 water at Walnut Grove, which lies approximately 8 miles above Isleton. 

 Results of catches made in these nets were compared with the flews at 

 their respective locations, and showed a phenomenal degree of correlation. 

 During the period March 26 through 30, Georgiana Slough was carrying 22.28 

 percent, of the total Sacramento River flow above its sources as calculated 

 from U. S. Bureau of Reclamation rating curves. The flow in Sacramento 

 River below the head of Georgiana Slough, was, of course, 77.72 percent 

 of the flow of the main stream as described above. Of the total number of 

 seaward migrants taken in the fyke nets, 22.56 per cent were taken in the 

 Georgiana Slough net and 77. Wi percent were taken in Sacramento River. 



It is recognized, of course, that the numbers of juveniles occupying 

 certain areas are limited by the volumes of water present in those areas. 

 It seems characteristic, however, that numbers tend to pile up in large 

 areas of open water that are susceptible to maximum tidal influence, as 

 the channel of the main San Joaquin River between its confluences with 

 Middle River and Seven Mile Slough. 



37 



