Most of the vessels used for taking plankton hauls could not he slowed dovna 

 sufficiently when the sea was fairly calm. At such times, the engine had 

 to be started and stopped frequently in order to approximate the desired 

 towing speed. More uniform hauling was possible when a moderate sea was 

 running (wind J^ or 5 on the Beaufort scale). The shallowness of the water 

 at some stations did not permit making hauls of the "usixal" depth. 



We have verified, by use of the depth-flow unit of an Isaacs high speed 

 sampler, that the depth of a plankton net at any instant during a haul can 

 be approximated by multiplying the amount of towing wire out by the cosine 

 of the angle of stray of the towing wire from the vertical (Ahlstrom 1952, 

 p, 4). The angle of stray of the towing wire is measured continuously during 

 a havtl by means of an inclinometer suspended from the boom and riding freely 

 on the wire. As uniform an angle as possible is maintained during a haul, 

 preferably a ^5 degree angle. The angle of ctray is recorded at half-minuto 

 intervals during a haul. 



To derive the average depth of a haul, D, the cosine of the average 

 angle of stray is multiplied by the length (in meters) of the towing cable 

 released in taking the haul. The cosine of the average angle of stray is 

 considered to be more representative of the haul as a whole than the cosine 

 of the angle of stray at greatest depth. 



STANDARDIZATION OF HAULS 



The "standard haul" that we employ adjusts the number of eggs or larvae 

 in a haul to the number in 10 cubic meters of water strained per unit of 

 depth fished by the net. If the vertical distribution has been encompassed, 

 as it has been for sardine eggs and larvae, this value is equivalent to the 

 number under ten sqiiare meters of sea surface. The standardization factor 

 for each haul (S, Factor) was derived from the formulatiouJ 



S » 10-S or lOJD 

 V R«a'p 



in which 



S - standardized haul factor 



D - the average depth of a haul 



The other symbols retain the same meaning as in the earlier 

 formulation. 



