434 DISCOVERY REPORTS 



Ruud and Fraser it is true have shown, or at any rate suggested, that the later larvae drift northwards 

 (and eastwards) in the Antarctic surface layer, or to be more precise in the Weddell stream, but no one 

 has yet shown, or even suggested, that they subsequently sink into the warm deep current to be carried 

 back to the south to mature. On the contrary, our bathymetric data show that perhaps the most 

 striking thing about the whole larval life-cycle is that as the development from Calyptopis One to 

 Furcilia Six proceeds (p. 112) the larvae, far from developing a downward trend, become more and 

 more restricted to the surface drift, never, at any stage in this developmental phase, becoming involved 

 in any mass descent into the warm deep stream. Nor is it certain that when they do mature they 

 produce surface eggs. 



Obviously, even so far as they are known, the factors controlling the distribution of this species 

 are complex, the problem as a whole presenting many puzzling features that perhaps for long will 

 remain to us obscure. And this must be true of other Antarctic plankton animals as well as of plankton 

 animals elsewhere, that as Dell (1952) has said 'have no obvious method of maintaining themselves in 

 the appropriate ecological niche '. 



In so far as the currents are concerned in the horizontal dispersal of the krill our observations 

 repeatedly show that their influence, as might be expected, is most marked during the feebly 

 swimming larval and post-larval phase. There is, I believe, horizontal dispersal in the deep bottom 

 water, in the warm intermediate layer and at the surface. But the greatest and most far reaching of 

 these movements, involving the northward and eastward transport of the larvae and their ultimate 

 spreading over the entire face of the Weddell stream, is in the surface drift. In the simplest of terms 

 we can say this movement has its roots in the highest latitudes of the krill's geographical range, being 

 engendered, as it is, by the great current that sweeps coastwise round the continental land, the East 

 Wind stream which Powell (1951), in his account of our Antarctic MoUusca, has described as a 

 'present' factor that 'must greatly facilitate the lateral distribution of many species'. 



One last point. It has been shown repeatedly that the krill as they grow tend to become less and 

 less strictly planktonic. A young, only half-grown, swarm for instance (p. 155) has been seen to 

 maintain its position close to a fixed point of reference for hours on end in face of a current of about 

 \ knot, and from this it would appear distinctly possible that the full-grown swarms in similar circum- 

 stances could hold their ground for days, perhaps for many days, on end. Could it not then be that 

 at least the breeders in the East Wind zone, where the average speed of the current is also probably 

 about \ knot, are to a large extent static, not for ever drifting to the west, but keeping station on fixed 

 points of reference for long periods, for all we know perhaps even throughout life} There must be 

 many such points all round the continental coast, rocks, rocky islets, islands, rocky headlands, the 

 ice-foot, the barrier faces, stranded bergs, even the ice-floes themselves, which, although in general 

 moving westwards under the influence of the prevailing wind and current, are often driven due north 

 by violent southerly gales, perhaps even out into the West Wind drift zvhere the current is travelling 

 east not west. If there should in fact prove to be a static population of spawners, or potential spawners, 

 in these high latitudes, and somehow or other we could explain their recruitment when eventually they die 

 off, then we should have a permanent and to some extent untapped nucleus of individuals from which 

 the northern population might spring. 



I end with a passage from the English translation of Paul Budker's recent book Baleines et Baleiniers. 

 ' Then, the future mothers being filled and the males satisfied — and there is nothing to make us think 

 otherwise — they set out for the south, to find once more the inexhaustible fields of krill, this profusion 

 of provender that is widespread, but not uniformly so, around the Antarctic Continent. And the 

 banquet is resumed, to go on until the next southern autumn. Then always in March to April the 



