bridle connected to several meters of line which attached to the 



towing cable by a clamp. A current meter was suspended in the 



center of the net mouth to measure volume of water filtered (see 

 Kramer et al., 1972, for further details). 



The standard tow from 1951 through 1968 was an oblique haul 

 to 140 m depth (to 15 m of the bottom in shallow areas) designed 

 to filter a constant amount of water per depth interval (ca. 

 3m 3 /m of depth) over the vertical range of most ichthyoplankters. 

 Hauls were made at a ship speed of 1.5-2.0 knots and initiated by 

 clamping the net line to the towing cable with the 4 5 kg terminal 

 weight about 10-15 m below the surface. The net was lowered to 

 140 m depth by paying out 200 m of wire over a 4 minute period 

 (35 m of depth/min.). After fishing at depth for 30 seconds, the 

 net was retrieved at 20 m/min. (14 m depth/min.). The angle of 

 stray of the towing cable was recorded every 30 seconds and 

 maintained at 45° (+3°) by adjusting the ship speed and course. 

 After reaching the surface, the net was washed down and the 

 samples preserved in 5% formalin buffered with sodium borate. 

 Flowmeter readings were made at the beginning and end of each 

 tow. Detailed descriptions of gear and methods are given by 

 Ahlstrom (1953), Kramer et al. (1972), and Smith and Richardson 

 (1977) . 



LABORATORY PROCEDURES 



Laboratory processing began with the determination of a 

 displacement volume for each sample (methods described in Staff, 

 SPFI, 1953 and Kramer et al . , 1972). Zooplankton volumes 

 (including ichthyoplankton) of samples collected in 1966 are 

 presented graphically in Smith (1971) . 



Sorting involved the removal of ichthyoplankton from the 

 sample and identification and separation of: eggs and larvae of 

 Pacific sardine and northern anchovy; larvae of Pacific hake; and 

 eggs of Pacific saury. In 1966, only one sample was fractioned 

 using a Folsom plankton splitter (McEwen, et al., 1954) prior to 

 sorting. This sample was collected on Cruise 6606, station 63.80 

 (see Table 1) . 



A "standard haul factor" (SHF) was calculated for each tow 

 to make them comparable and allow estimations of areal abundance. 

 This factor adjusts the number of eggs or larvae in a haul to the 

 number in 10 m of water strained per meter of depth fished. If 

 the vertical distribution of the species has been encompassed^ 

 then the adjusted value is equivalent to the number under 10 m 

 of sea surface. The SHF is calculated for each haul by the 

 formula: 



SHF = 10 D 

 V 



