A rapid decline in the downstream escapement of Sacramento River 

 salmon in cycles 10 and 11 accompanied a decrease in Sacramento flows. 

 A sudden rise in Sacramento River flows in the 12th towing cycle was 

 followed by an increase in the downstream movement of fish from that 

 source. Juvenile salmon from the Sacramento River drainage continued 

 to enter the Delta until June 9, 191*9 (Cycle 20) with a proportionate 

 number of individuals moving down Georgiana Slough. No further record 

 of regular downstream movement was noted from the stations in the upper 

 Sacramento River and Georgiana Slough, indicating completion of seaward 

 migration from that source. 



The average lengths of the station samples of Sacramento migrants 

 from the beginning of towing through the peak period of abundance, end- 

 ing with the 9th cycle, was 35-U5 mm (l.b-1.7 inches). A gradual in- 

 crease in growth continued until the 12th cycle, April 11, when migrants 

 of a larger size-class began appearing in the samples. By the last week 

 of April, lljth cycle, the majority of station samples of Sacramento sal- 

 mon were 50-70 mm (2-2.7 inches). From the beginning of May to the end 

 of the seaward migration, Sacramento migrants averaged 70-90 mm (2.7- 

 3.5 inches). 



Six weeks after the initial arrival of Sacramento River seaward 

 migrants in the Delta, those from the San Joaquin River drainage began 

 entering the southern Delta waters. Specimens were recovered at 

 stations 2, 8, and 12 in the 11th cycle (Fig. h) . Their time of 

 arrival was approximately the same as in the previous year and con- 

 sisted of fingerlings ranging from 2.$ to 3.0 inches in mean length. 

 The appearance of the San Joaquin River migrants reflected a spontaneous 

 seaward movement, inasmuch as it was not influenced by increasing river 

 runoff. Quite to the contrary, the San Joaquin River flow was receding 

 and continued to do so for the succeeding three cycles. Significant 

 numbers of salmon migrants were taken in the southern Delta stations 

 in the ensuing nine cycles, to indicate a comparatively greater 

 escapement than that of the previous year (Appendix Table 6) . Through- 

 out the season, stations in channels converging on the approach canal 

 of the Tracy Pumping Plant yielded the largest catches (Fig. h). One 

 catch of 119 salmon fingerling averaging 71. h mm (2.8 inches) was made 

 in a standard tow from station 3 during the lUth cycle. Continuous 

 migration from the San Joaquin River was evident through the 22nd 

 cycle, June 20-23 , 19u9« Thereafter, only an occasional individual 

 was recovered in the southern Delta channels. During the 25th and 

 26th cycles, water temperatures in the southern Delta reached a 

 maximum of 80 degrees Fahrenheit. 



One role of water temperatures in controlling the movements of 

 immature salmon in the Delta is suggested by information presented in 

 Fig. 9, which features a graphic summary of tow-net catches, together 

 with a temperature curve based on five Delta stations. It is seen that 

 after the mean daily water temperatures surpassed 75 degrees in 19I18 



19 



