Standard methods of fishing the various nets were adopted. The 

 eggs j larvae, and juvenile fish taken by these methods are considered 

 indicative of their relative abundance and distribution in the Delta. 

 Two types of plankton net hauls were made: surface tows just below 

 the water surface, and deep tows at depths of 13 and llj. feet. The net 

 was towed fifty feet astern of the launch for five or ten minute periods, 

 depending on the amount of detritus in the river. The five-foot tow-net 

 hauls were made just below the surface with the net towed 100 feet 

 astern of the launch for 30 minutes. The towing speed was kept constant 

 by tachometer readings. During 19h9, a Price current meter suspended 

 in the water from the bow of the launch was used in conjunction with 

 the tachometer readings to keep the towing speeds as nearly constant as 

 possible under operating conditions. The towing speed of the plankton 

 hauls was approximately four feet per second. The five-foot surface 

 net was hauled through the water at an approximate rate of six feet per 

 second. In determining the relationship of the velocity of the water 

 strained through the nets to the velocity of the flow past the nets, a 

 series of tests were made with a Price current meter mounted in the 

 center of the mouth of the nets and another suspended from the bow of 

 the towing vessel as in actual operation. The mean velocity of the 

 flow through the standard five-foot tow-net with bobbinet lining com- 

 puted from 185 readings was 5.8 feet per second compared to 5.95 feet 

 per second, the velocity of the net through the water. Similar tests 

 with the half-meter plankton net computed from k9 readings gave a mean 

 velocity of 3-36 feet per second through the net compared to 3.92 feet 

 per second, the velocity of the net through the water. 



Exploratory net towing operations were conducted in the Delta 

 channels for several months. This preliminary work permitted (l) selec- 

 tion of standard methods of sampling for each type of net, (2) recon- 

 naissance of Delta channels for suitable stations, and (3) observations 

 of the hydrodynamics within the Delta. 



As a result of the exploratory work, twenty-five stations were 

 selected as the minimum number necessary to obtain reasonable coverage 

 of the Delta. The locations of the stations are illustrated in Figure 

 1. Stations 1 to 5 were established during the preliminary operations 

 and the remainder were included in the operation schedule after March, 

 19U8. One complete coverage of all stations is referred to as a cycle. 

 During 19u8, nineteen cycles were completed. The cycles varied from 7 

 to 1)4 days in duration and were repeated as frequently as possible. 

 Four- stations in the central Delta area were relocated in 19^9 in order 

 to give better coverage, and an additional tow-net station was estab- 

 lished on April 11, 19U9 in the main stem of the Sacramento River off 

 Chipps Island. The relocations were not drastic in nature, as demon- 

 strated by subsequent checks. The I9U8 locations of the stations which 

 were relocated are indicated in Figure 1 with broken line circles. The 

 following list sets forth the old and new locations of the tow-netting 

 stations in the Sacramento-San Joaquin Delta; 



Opposite: Figure 2 -- Location map of stations in Sacramento -San Joaquin Delta 



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