August h=17, 19U8« Stations in the southern Delta in the vicinity of 

 the Tracy Pumping Plant yielded representative samples of striped bass 

 through the llrth cycle. The diminishing catches of striped bass in the 

 tows from the lUth cycle to the 17th cycle were probably due to the move- 

 ment toward the lower bay, mortality, ability of the young to escape 

 the tow-nets as they increased in size, and adaptation of adult 

 characteristics of schooling and feeding nearer the bottom. 



Weekly coverage of established stations in 1°U9 proved to be 

 an improved means of sampling striped bass and gave a better re- 

 lative measure of distribution of bass eggs, larvae, and juveniles in 

 the Sacramento^San Joaquin Delta, than in 19U8. 



Results of sampling for striped bass eggs in 19^9 are summarized 

 in Appendix Table 11 „ This sampling generally consisted of three 

 plankton-net hauls of five minutes duration at each station. Two sur- 

 face tows were made, one at the beginning of the station and the second 

 at the end of the .station. The five-minute deep tow was usually made 

 at the terminus of the station at a depth of 13-lU feet. Several sta- 

 tions in the southern Delta channels were too shallow to risk the loss 

 of the net, so sampling was limited to the two surface hauls. 



The first evidence of striped bass spawning was observed in San 

 Joaquin River near Mossdale, station 11, in the 11th cycle (April 5-7, 

 19U9), when two eggs were recovered. By the end of the next cycle 

 (April 11-15, 19^9) spawning activity was occurring in several scattered 

 locations in the San Joaquin Delta. Significant catches of bass eggs 

 were made in the southern part of the Delta through the major period of 

 the spawning season. Increasing numbers of eggs were caught in successive 

 towing cycles, with new stations added to the growing list. The peak period 

 of spawning activity extended from the last week in April to the middle of 

 May. 



Observed water temperatures ranged from 57 degrees to 65 degrees 

 Fahrenheit at the start of the spawning (April 5-7, 19^9), and generally 

 were above 60 degrees at the stations where eggs were taken. At the 

 close of the spawning season (June 15-17, 19h9) water temperatures 

 in the Delta ranged from 69 degrees to 78 degrees Fahrenheit. 



Assuming that the number of eggs recovered from week to week in 

 the San Joaquin Delta is an index of spawning intensity, it is evi- 

 dent that the initial spawning was heaviest in the southern and central 

 portion of the Delta, with a gradual shift to the western or lower San 

 Joaquin River portion,, Very few eggs were taken at stations located 

 in Sacramento and Mokelumne Rivers. As in I9I48, the most productive 

 area was San Joaquin River from the mouth of Old River to Antioch. 

 This concentration of eggs in the lower section of San Joaquin River 

 was probably due to the eggs drifting with the net outflow of water, 

 particularly tvith respect to the eggs recovered on station 17. Station 

 17 was apparently the lower limit of the outward drift of eggs. This 

 was evident from the small number of eggs recovered from station 26, 

 which was downstream from station 17. 



25: 



