METHODS OF SAMPLING 



Plankton nets used during 1957 were either constructed of No, 30xxx grit 

 gauze, a heavy grade of silk bolting cloth, or No, 471 "Nitex", a nylon mono- 

 filament screen cloth. The mesh opening of Nitex cloth measures approxlmktely 

 0.47 mm. The mesh opening of No. 30xxx grit gauze measures approximately 

 0.70 mm, before use, but soon shrinks to approximately 0.55 mm. between 

 threads. Mesh openings in nets constructed of Nitex tend to enlarge slightly, hence 

 the mesh openings of the two kinds of cloth, after use, are not too dissimilar. 



The rapidity with which nylon cloth dries has proved to be a liability in plankton 

 sampling. Unless a nylon net is very thoroughly washed after each use, any adhering 

 plankton dries against and clings to the nylon threads, soon causing the nets to clog 

 badly. Plankton nets are hosed down after each haul, but only scrubbed at intervals 

 during a cruise, SUk nets, which dry more slowly and consequently remain damp 

 between stations, do not develop this type of clogging problem. 



Plankton hauls are made obliquely from approximately 140 meters deep to the 

 surface (200 meters of wire out at greatest depth) where depth of water permits; 

 at lesser depths in shallow water. The research vessel moves slowly ahead during 

 a plankton haul, usually at a speed of between 1 and 2 knots. The amount of water 

 strained during a haul is determined from the revolutions registered by a current 

 meter fastened in the center of the mouth of the net. 



ABUNDANCE OF FISH LARVAE IN 1957 



Fish larvae were more abundant In 1957 than in the preceding two years, as 

 is shown by the average number of larvae obtained per station (standardized counts): 



Number of stations Total number Average per 

 Year occupied of larvae station 



1955 1375 359,155 261 



1956 1397 408,140 292 



1957 1493 493,549 331 



