METHODS OF SAf-lPLING 



The nets used in the collection of fish eggs and larvae were construo- 

 ted of No. JOxjcs. grit gau'/.e, a heavy duty grade of silk holting cloth. The 

 openings 'between meohes in this material are approximately O.65 mm. when 

 new, shrinking to approximately O.50 mm. after use. The nets were conical 

 in shape, 1.0 meter in diameter at the mouth and approximately 5 meters in. 

 length. A current meter was placed in the center of the mouth of each net 

 to register the flow of water into the net during a haul. 



The nets v/ere hauled obliquely from approximately 1^ meters in depth 

 to the surface (200 meters of wire out at greatest depth), except at Bhallow 

 stations. The hauls were made at a vessel speed of about 1-| to 2 knots. 

 The hauls differed from those made in previous years in one respect: the 

 depth of the stratujn sampled was approximately doubled. Previously the 

 hauls had averaged about 70 meters in depth (net lowered on 100 meters of wire), 



HBjiJSUBEMENI OF VOLUME OF WATER STHAIlOiD DURING PLANKTON HAULS 



An Atlas type current meter was suspended in the mouth of each net. 

 This instrument consists of a rotator and revolution counter housed in an 

 open cylinder. The water entering the net during a haul actuates the freely 

 running rotator, which is geared to the revolution counter. A reading of 

 the counter was made before commencing a plankton haul, and again on the com- 

 pletion of the haul, 



Current meters were calibrated before and after each cruise on which 

 they were employed. During calibration trials, each current meter v/as hauled 

 over a measured distance at a range of speeds. Performance graphs were con- 

 structed in which the independent variable was the speed of towing (revolu- 

 tions per second), the dependent variable the length of the column of water 

 in meters that was needed to effect one revolution of the current meter at 

 any given towing speed. Since performance tests were made before and after 

 each cruise, the graph applicable to a given cruise was based on two cali- 

 bration trials. In text table 3, current meter performance data are given 

 for the current meters used during 1951 • 



The consistency in the performance of Atlas type current meters can be 

 judged from this table. Current meter No. 88, which was used on eleven 

 ciniises during 1951 1 was quite consistent in performejice throughout the year. 

 Current meter No. 82, used on six cruises, gradually became more free-running 

 with cont indued use. 



