CLaSSIFICATION OF MA.TERIAL 



SgRS and larvae viere of course treated separately. Also, to take ac- 

 count of the fact that motility increases with size of larvae, these v.'ere 

 divided into tivo categories: "large" and "small". A dividing line of 8 imn, 

 had previously been used in other vrork, vfith '^vhich it was desired to compare 

 the results of this analysis. Since this line did not split a mode in the 

 length frequency distribution of larvae in the vertical serial hauls, it 

 was retained for the present study. 



Some larvae of the "small" group v;ere lost through the meshos of the 

 one-meter nets used. This, however, does not necessarily invalidate com- 

 parisons between numbers caught at different levels with the same net, since 

 the loss should be a constant percentage of the total number caught. 



ST.'U'JDAHDIZATION OF HAULS 



Because of unavoidable variations in the speed bl the ship and time 



of hauling, the amount of water strained by the net varied from haul to 



haul, even within a single series. These variations were discounted by 



putting all the hauls in each series on the basis of a standard volime of 



water strained. For the 1939 hauls, flow of -vatar through the nets i:as 



measured directly oy a current meter, but for the 19U1 hauls, the relative 



, Wi tan/1 i Wi 

 amount vras computed fro.n the formula ■»»- = L . virhere --- = the ratxo oe- 



"'2 tan/2 ^ 



tween the amounts of v;ator strained for any tv/o hauls,, and /i and /2 = their 

 respective stray angles. Actual volumes of ■vfater strained averaged around 

 UOO cubic meters for the one-meter nets, and 100 cubic meters for the half- 

 meter nets. The numbers of organisms in the hauls were multiplied by fac- 

 tors (Vs^ v/here Vg = standard volume of water and Vj^ = volume strained in 



Vh 

 given haul) v;hich made the numbers the same as if the standard volume of 

 water had been strained, and had contained the saine-concentration of organ- 

 isms as the water actually strained. 



Because of the great range i:i nuribers of organisms (from 6 to 6,000 

 in a single series of hauls) they could not be represented graphically 

 on the same scale. Since the change in concentration from one series to 

 another was not of interest, but only the changes froia haul to haul within 

 a series, the graphing difficulty v:as overcome by representing pach vertical 

 series by a polygon of equal area. To do this, the product of hunibers of 

 organisms by thickness of layer sampled was obtained for each haul. These 

 products were sujniaed f-or each station, and the original counts of organisms 

 v/are multiplied by factors which made the sum of such products a constant 

 for all stations. Besides overcoming the graphing difficulty, this compu- 

 tation placed the, numbers at each level for all of the stations on a com- 

 parable basis, permitting direct comparison of catches at different levels 

 even though they vfere not taken at the same station. 



To avoid excessive randoa variability froa small numbers., series con- 

 taining less than 100 eggs, 50 small larvae, or 5 large larvae, were omitted 

 from the analysis. 



183 



