212 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



torted specimens were classed by matching them with straight specimens of known 

 length. 



The method of converting the counts to total catch was simple in the majority 

 of instances because usually the mackerel material consisted either entirely of eggs and 

 small larvae, so that the total catch could be computed directly from the known 

 volume of sample sorted and the known volume of the plankton from which the sample 

 was drawn; or entirely of large larvae sorted from the entire catch, so that a simple 

 count represented the total. In a minority of instances, when both small and large 

 larvae occurred in the same haul the total had to be computed from a combination of 

 the sampled numbers of small larvae and the total numbers of large larvae. 



The specimen tabulation (table 14) illustrating the computation is self- 

 explanatory except for the treatment of those sizes of larvae which were too scarce 

 to be adequately represented in the small sample. Referring to columns 2 and 3 

 of table 14, it is obvious that the numbers of 8-mm. larvae were too few to have 

 been taken in the smaU sample and also that in sorting the remainder, larvae as 

 small as 6 mm. and perhaps also 7 mm. were not fully removed. Therefore, the 

 3- to 6-mm. larvae, inclusive, in the small sample were taken as representing the 



catch of these sizes and the items of column 2 were multiplied by ^r~r and entered 



in column 4. The numbers (2) in the 7-mm. category in the small sample (column 2) 



were taken as representing the numbers of larvae 7 mm. and over, which should then 



2,000 

 total 2 X ' =36 in the entire sample. Since there were known to be 6 larvae 



of 8-mm. length (column 3) in the catch, the entry of 6 was made opposite the 8-mm. 

 class in column 4 and the entry of 36 — 6 = 30 opposite the 7-mm. class. The count of 

 larvae in the lower haul (table 14) included no larvae larger than those found in the 

 small sample, and the total numbers of each size (column 8) were computed simply 



by multiplying the counts in the sample (column 6) by ' . 



Table 14. — Specimen computation for converting counts of eggs and larvae to total catch on the standard 

 basis of 17.07 cubic meters of water strained per meter of depth fished 



[Data relate to station 21491] 



