284 DISCOVERY REPORTS 



figures that in most instances are manifestly far from representative of the natural abundance of the krill 

 in the sea. As Hardy (19586) has said, ' The use of nets in the sea is really an experiment, an experiment to 

 see if the net, by being used in a certain way, and at certain intervals of time and space, can fix an 

 adequate series of samples which will represent the actual distribution of the animals concerned in nature '. 

 It could be argued that my factor for the oblique-horizontal ratio is too low, that since the hori- 

 zontal net spends ^ hr. at the surface, as against only about 2 min. by the oblique, it should be 1 5 

 instead of 4. This could well be, but only if (i) the krill were scattered broadcast evenly throughout 

 the surface zone, and not, as they are, in rather widely separated swarms, and if (2) the surface net 

 during its ^ hr. in the water struck a narrow swarm a mile or so long and fished all along, not across, 

 it. That this should happen, however, is extremely unlikely, the swarms that have been seen as a rule 

 being of vastly smaller dimensions. Moreover, if 15 is indeed the ratio we should expect a figure of 

 this order to show up when the average catch-figures for an enormous number of oblique and surface 

 net hauls were compared. We find, however, looking at the figures for the staple whale food, that the 

 average catch of 732 night oblique hauls is 391, of 1013 day oblique hauls 278 (Table 56) and of 

 357 night surface hauls 840 (Table 50). This does not suggest that the ratio need be very high or 

 indeed that the surface net is all that vastly more efficient than the oblique. Even if the enormous catch 

 of over 200,000 (Table 50) be included in the night surface total, the average, 1397, still works out 

 at only three and a half times the average oblique catch by night and only five times the average 

 oblique catch by day. But perhaps the overriding consideration is this. Whether the factor (or factors) 

 used to express the oblique in terms of the surface catch be high or low, in the end it only serves to 

 heighten the overwhelming importance of the East Wind-Weddell surface stream as a carrier of the 

 larval, adolescent and adult krill. I found this repeatedly during my early attempts to portray the 

 distribution, when, before all the data finally came to hand, I was using a factor of 8. The same overall 

 picture, massive East Wind-Weddell abundance and scarcity in the West Wind zone, is obtained 

 without using any factor at all, as I again found when I originally began plotting our data using the 

 oblique catches alone, and as they stood. A striking example of this is provided by Fig. 157 

 (p. 425) which shows the gross distribution and relative abundance of the krill based exclusively on 

 oblique (loo-o m.) gatherings. Above all, turning to the situation in the East Wind zone, the correc- 

 tions applied to the catch-figures there have their own especial value in so far as, I feel sure, they help 

 greatly to offset the heavy disadvantage (p. 59) under which so many of our samples were collected 

 in these high, virtually nightless, summer latitudes. 



HORIZONTAL DISTRIBUTION, GROWTH AND 

 DYNAMICS OF DISPERSAL 



Introduction and plan of presentation 

 In the following section the horizontal distribution of the krill, already broadly outlined on pp. 57-64 

 (Figs. 5 a, 56 and 5 c) and the factors controlling it are described in detail, the matter presented 

 covering every phase of the developmental history from the egg to the adult state. The distribution 

 is illustrated on two sets of circumpolar charts, one based on the data from the vertical nets, the other 

 on the data from the horizontal (0-5 m.) and oblique (loo-o m.) stramin nets, the gatherings of the 

 latter with the standard corrections applied where necessary as described on pp. 282-3. The vertical 

 net series deals exclusively with the eggs and both deep and shallow living larval forms, the stramin net 

 series with the surface larvae, the young, very small and occasionally eaten adolescents (the small 

 whale food) and Avith the older adolescent and adult krill (the staple whale food) which constitute 

 the bulk of the diet of the baleen whales. 



