DISTRIBUTION IN OUTLINE 59 



compelled to ignore them and to turn to the gatherings of the useful though less efficient oblique net 

 before any reliable estimate of the actual abundance of the population in this, it seemed, krill-rich 

 zone could be made. At many stations too in more northerly waters, where there are dark nights to 

 work in, the surface net even in darkness was never fished, so that much of our data from both high 

 and low latitudes does in fact come from the oblique net alone. 



In so far then as surface nets were concerned it was clear that in the higher latitudes, with their long or 

 continuous hours of summer daylight, our sampling of the krill was being conducted at a distinct dis- 

 advantage. In short it became obvious, having regard to the greater sampling power of the horizontal 

 net when used on the surface in northern darkness, that the oblique net, upon which we had so largely 

 to rely in the East Wind zone, was not providing us with a true picture of the abundance of the krill in 

 this coastal stream, nor was it doing so in the lower latitudes where it alone was so widely used. 



In view of the manifest disadvantage under which the summer East Wind samples were collected, 

 and of the lesser efficiency of the oblique vis a vis that of the night surface net, it became clear to me 

 that a true and unbiased picture of the relative abundance of the krill in the circumpolar sea could not 

 in fact be presented until these differences had been resolved. Briefly and simply I did this by taking 

 the gatherings of the surface (0-5 m.) and oblique (loo-o m.) nets and comparing them at all stations 

 where both nets night and day were fished simultaneously, finding that, taking the surface population 

 as a whole (but ignoring the valueless data relating to the escaping over 20 mm. population provided 

 by the surface nets in daytime), on the average the surface net was twice as efficient a sampler of the 

 larvae and four times as efficient a sampler of the adolescents and adults as the oblique, the adolescents 

 and adults referring to all individuals over 15 mm. long. In all instances, therefore, where oblique 

 nets alone were used, or where, as in daylight surface nets, if used, could not, or virtually could not, 

 sample the escaping (over 20 mm.) population, the gatherings of the oblique nets have been multiplied 

 by 2 or 4^ as requisite in order to bring them into line with the higher orders of abundance repeatedly 

 revealed by our surface nets. A correction has also been applied to all towed net samples to equate 

 them to a 30-minute haul; for example the catch of the 20-minute oblique net fishing through loo-o m. 

 is multiplied by 1-5 to the nearest whole number. 



Much of more general biological interest has also come out of this investigation, but as I have said 

 presentation of full details has been deferred and only major findings mentioned here. I have deferred 

 the matter deliberately so that the reader approaching the main distributional part which begins on 

 p. 284 will come to it with the full facts of the sampling, and above all with the corrections applied to 

 certain catch-figures, freshly stamped in his mind. In the meantime it should be noted that the 

 further corrections explained on pp. 278-84 have been applied as necessary to the quantities shown in 

 certain tables and figures, especially in the construction of Tables i, 2, 37, 39 and 47, and of 

 Figs. 56, 5c, 13, 24, 25 and 26. They do not, however, bias such general conclusions as have been 

 drawn either from these five tables or six figures. The same conclusions can be drawn, and in fact 

 originally were drawn, ^ from data presented without them. 



Whatever value they may have elsewhere it is above all in the East Wind zone, with its virtually 

 nightless summer, that their usefulness comes most to the fore, in so far as they serve to offset there 

 the severe handicap under which so much of our material was collected. 



The gross or absolute distribution of this species, based on every occurrence we have recorded from 

 the egg to the adult state, is shown in Fig. 5 a and the distribution of its major concentrations, based 

 on gatherings of not less than 1000 in the stramin nets and of not less than 100 per 1000 m. vertical 

 haul, in Fig. 5 b, the figures together presenting in sharp relief such regions as have repeatedly been 



1 See p. 279, Tables 57-60. 



- In the course of many early and long since rejected attempts to tabulate our data and plot it on the charts. 



4-2 



