METHODS OF SAMPLING 



Plankton samples were obtained by obliquely hauling a conical net, 1,0 

 meter in diameter at the mouth, from approximately 140 meters deep to the sur- 

 face, except at shallow stations. The nets were constructed of No. 30xxx grit 

 gauze. The depth range fished by the net during each haul is given in column 

 8 of the extended table in Special Scientific Report: Fisheries, No. 100. The 

 hauls were made at a vessel speed of about 1-1/2 to 2 knots. The water enter- 

 ing the net during a haul was measured by a current meter fastened in the mouth 

 of the net. The volume of water strained while taking each haul in 1952 is 

 listed in column 7 of the table referred to immediately above. The methods of 

 deriving volume of water strained during a haul from current meter readings, 

 and of standardizing hauls for comparability are discussed in a preceding re- 

 port (Ahlstrom 1953: 4-6). 



SEPARATION OF FISH EGGS AND LARVAE FROM PLANKTON SAMPLES 



Plankton hauls obtained on the 11 survey cruises made during 1952 totaled 

 1475. In working up the samples in the laboratory, the volumes of plankton 

 were first determined (cf . , "Zooplankton volumes off the Pacific coast, 1952? 

 Special Scientific Report: Fisheries, No. 100), the larger samples were frac- 

 tioned into aliquot portions (2, 4» 8 or 16), and the samples or aliquota 

 were examined under a low power binocular microscope in order to separate fish 

 eggs and larvae from other plankton organisms. Approximately l/6th of the 

 samples were fractioned into aliquot portions before examining; the remaining 

 5/6ths were examined in entirety. A single aliquot portion was sorted of each 

 fractioned sample. Information, by cruise, on the number of samples examined 

 in entirety and those which were fractioned, is given in text table 4. 



Text table 4.- Laboratory examination of the 1952 plankton samples. 



Total 



10 



52 



171 



1239 



1475 



