During 19h9 improved coverage of the Delta was made possible with 

 an increase in the number of personnel, and the addition of a second 

 launch. This permitted dividing the Delta into two areas s one included 

 all stations located in the Sacramento Delta, Mokelumne River, and those 

 stations situated in the San Joaquin Delta below the mouth of Old River) 

 the other area included all stations located in the San Joaquin Delta 

 above the mouth of Old River. Each area was assigned a launch and 

 operating crew. A minimum of eight stations was sampled daily, with 

 a cycle of all stations completed in a period of three days. Thirty- 

 three weekly cycles were completed from January 25th to September 22nd, 

 I9h9. 



The fishes, post-larval and juveniles, taken alive, were measured 

 in the field and returned to the water. Specimens killed in towing 

 operations were measured and then preserved in five percent formalin. 

 Measurements were made to the nearest millimeter from the anterior tip 

 of the head to the fork of the tail. Plankton-net catches were examined 

 in the field for striped bass eggs and larval fishes when time allowed) 

 otherwise, the samples were preserved in five percent formalin and sorted 

 at headquarters. Identification of the larval striped bass and shad was 

 checked with the aid of the following references: Pearson (1938), Merriman 

 (19h0), Leim (I92li), and Leach (1925). Through the courtesy of Dr. A. J. 

 Calhoun, of the California Division of Fish and Game, identified speci- 

 mens of eggs and larvae were made available for aid in identification of 

 our material. 



In order to determine the distribution of the immature salmon, striped 

 bass and shad in the Delta, it was necessary to calculate relative abundance 

 of each species at each tow-net station. The calculation was based on the 

 assumption that the horizontal and vertical distribution of the fish was 

 uniform and that the thirty-minute tow-net sample was representative of 

 conditions at the station. Since the tow net had a diameter of five feet 

 and was towed immediately beneath the surface, the calculation was limited 

 to the upper five feet of depth. The mean width of the station was determined 

 from U. S. Corps of Engineers maps of the Delta channels (1933, 193k, and 1936) . 

 The average width of the channel in feet at the station was multiplied by five 

 to obtain the cross-sectional area involved. The cross-sectional area was then 

 divided by 20 square feet, the cross-sectional area of the tow net, and the 

 dividend was multiplied by the number of young fish of each species taken in 

 the station. In this manner, adjustments were made for the differences in 

 width of channels at station sites. The relative numbers of salmon, striped 

 bass and shad thus obtained were assumed to represent the abundance of young 

 fish in the area sampled. The calculated results for the three species are 

 illustrated graphically in independent series of maps, showing the cyclic 

 distribution of each species in the Sacramento-San Joaquin Delta in 19U8 

 and 19U9 as determined from tow-net sampling. On the graphic illustrations, 

 the area of each circle is proportional to the calculated number of specimens 

 at each station. The mean length of the measured sample from each station is 

 given with each circle. The hydrodynamics occurring during the cycle are 

 included,, showing mean Delta inflows in cubic feet per second, maximum and 



