VERTICAL DISTRIBUTION OF ADOLESCENTS AND ADULTS 323 



hours when the loo-o m. NiooB would not normally be expected to take a representative sample 

 of the species owing to its diurnal vertical movements. However, at several day stations on the shelf 

 nearly the whole water column was sampled, the net fishing to within 20 m. of the bottom, so unless 

 the larvae were lying either on or very close to the bottom, for which there is no evidence one way or 

 the other, these stations can be used as evidence of the presence or absence of E. triacantha. Night 

 stations are indicated in the figure by the letter N. 



It can be seen that, although moderately large catches of larvae were taken off the edge of the shelf 

 even in daylight, they were only taken at two stations inside the 200 m. contour and there was only 

 one larva at each of these. 



VERTICAL DISTRIBUTION OF ADOLESCENTS AND ADULTS 

 In considering the vertical distribution of E. triacantha it is necessary to take into account the diurnal 

 vertical migration, the existence of which was shown by Mackintosh (1934, 1937) and Hardy and 

 Gunther (1935). Mackintosh, while studying the effect of diurnal variations upon the catches in the 



Table 3. Diurnal variation in the numbers of adolescent and adult Euphausia triacantha 

 taken at stations within its normal horizontal range by the lOO-o m. NiooB 



Mean no. E. triacantha 

 Total no. No. of % of Total no. of Mean no. E. triacantha per haul, 



of hauls positive hauls positive hauls E. triacantha per haul. All hauls Positive hauls only 



Day 379 6 i-6 17 0-045 2-8 



Night 430 292 67-9 4016 9-340 13-8 



loo-o m. NiooB, found that E. triacantha was taken in only three out of 127 hauls made between 

 0600 and 1759 hrs. This diurnal variation in the numbers in the upper 100 m. is confirmed and shown 

 to be even more marked by the present data. It will be seen from Table 3 that of 379 hauls taken 

 during daylight hours within the horizontal range of adolescent and adult E. triacantha (see Table 4) 



Table 4. The approximate northern and southern limits 0/ Euphausia triacantha in each 10° of longitude. 

 Only stations falling within these limits have been used in assessing diurnal migration 



