RECORD OF STANDARDIZED HAUL FACTORS FOR OBLIQUE HAULS 

 MADE WITH PLANKTON NETS DURING CRUISES 5501-5512, 1955 



The number of fish eggs or larvae in a haul is adjusted to the 

 number under 10 square meters of sea surface. This estimate is a valid 

 one if the vertical distribution of eggs and larvae has been encompassed. 

 For all species included in this report, except hake larvae, this require- 

 ment has been met. Routine plankton hauls average between 130 and 140 

 meters deep. From vertical distribution studies, we have established that 

 larvae (and eggs) of the sardine, anchovy, jack mackerel. Pacific mackerel 

 and rockfish seldom occur as deep as 100 meters, hence the layer sampled 

 in taking a plankton haul is ordinarily at least 30 or 40 meters deeper 

 than the depth distribution of the larvae. About 10% of hake larvae taken 

 in special vertical distribution studies was taken below 140 meters; there- 

 fore, the abundance of hake larvae is probably underestimated by this 

 amount. 



A standardized haul factor is given for all plankton hauls taken on 

 routine cruises during 1955 (except "Norpac"). Additional information on 

 these hauls, including position, date and time of collection, volume of 

 water strained, and depth of haul in meters, has been given in 'Zooplank- 

 ton volumes off the Pacific coast, 1955" (Special Scientific Report - 

 Fisheries No. 177). 



A dash (-) in table I indicates that the station was not occupied on 

 the cruise under which it appears; N.Q. - haul not quantitative; N.S. - 

 station occupied, but sample either not obtained or subsequently spoiled, 

 broken, or lost; S.T. - only surface tow taken. 



A measure of the volume of water strained during each haul was de- 

 rived from current meter readings. An Atlas-type current meter was fas- 

 tened in the center of the mouth of each net. The meters were calibrated 

 before and after each cruise on which they were used. 



Plankton nets used during 1955 were either constructed of No. 30xxx 

 grit gauze, a heavy grade of silk bolting cloth, or No. 471 "Nitex", a 

 nylon monofilament screen cloth. The mesh openings in the Nitex cloth 

 measure approximately 471 microns. This cloth has been subjected to a 

 thermosetting operation which imparts a permanent crimp to the fabric, 

 giving it good stability. The mesh openings in the nets constructed of 

 grit gauze are slightly larger than in the nets constructed of Nitex, how- 

 ever the grit gauze shrinks on use to approximately 0.55 mm. between threads, 

 while the mesh openings in Nitex tend to enlarge slightly. Nets construc- 

 ted of silk grit gauze are more easily cleaned and clog less than nylon 

 nets, but they have a considerably shorter life. 



