water transferred to the Delta. Some of the diverted fish moved seaward 

 down the San Joaquin River while others were dispersed further into the 

 central Delta waters. Contrary previons to opinions, Sacramento River 

 salmon remained in the San Joaquin Delta for a period of time. Young 

 salmon of Sacramento River origin were taken on successive towing 

 cycles at station 13 in the San Joaquin River, Station 6 in Old River 

 and station 10 in Middle River (Fig. 2). This distribution of the 

 Sacramento and possibly Mokelumne River salmon migrants within the 

 Delta was due to circulation of Sacramento water into the San Joaquin 

 Delta by flow and tidal action. 



Salmon migrants from the San Joaquin River were noted in the first 

 towing cycle, April 9-l6, above and below the bifurcation of the San 

 Joaquin and Middle Rivers (Fig. 3). Absence of young salmon in the 

 Delta channels between station 8 in Middle River and station 6 in Old 

 River separated the two groups. The mean lengths of station samples of 

 Sacramento salmon (stations 6, 7, and 13-25,) ranged from 38~69mm (1.5 

 to 2.7 inches), and corresponding mean lengths of San Joaquin fish 

 (stations 1, 2, 3, 5, 8, 11, and 12), ranged from 6$>-8bnm (2.7 to 3.3 

 inches) during the first and second cycles and salmon from each source 

 were separable by this difference (Appendix Table 5). Intermingling 

 of the two groups of salmon was inevitable, and by the end of the 

 third cycle it was impossible to differentiate the two groups of fish 

 since a size group of Sacramento River salmon corresponding in size 

 to the San Joaquin fish had also entered the Delta. Representative 

 samples of young salmon were taken at all stations as the season ad- 

 vanced, with the largest catches continuing from the Sacramento Delta 

 and the western and central San Joaquin Delta. The diversion of 

 Sacramento salmon via Georgiana Slough, and their dispersal within 

 the central San Joaquin Delta continued to be reflected in the tow- 

 net catches from this area. 



The seaward movement of young salmon migrants from the San Joaquin 

 River system did not reach expected proportions during the year of 19u8. 

 Drought conditions in the San Joaquin Valley were severe, and practic- 

 ally prohibited the escapement of immature salmon from San Joaquin River 

 and its tributaries, which are still considered good salmon spawning 

 grounds. At no time during the migration period did the number of 

 salmon migrants caught in the southern San Joaquin Delta equal or even 

 approach the number caught in the Sacramento and the western and cen- 

 tral parts of the Delta. The juvenile salmon entering the Delta from 

 San Joaquin River were dispersed principally via Middle River to 

 Salmon Slough, Grant Line Canal, and then down Old River. The progress 

 of San Joaquin salmon through the Delta was slow. By the end of June 

 the last salmon migrants from the two main river sources had apparently 

 entered the Delta. The seaward movement of young salmon from the Delta 

 extended through July, but negative catches in August indicated that they 

 had left the Delta waters. 



15 



