THE OLDER STAGES 169 



surface.! In fact, as far as appearances go, of the known species of large, or moderately large, baleen 

 whales only the Californian grey it seems could be described as a deep, or at any rate moderately deep, 

 feeder, stomachs of this strictly neritic species having been reported to contain material from the 

 bottom, amphipods, polychaetes, hydroid polyps, Buccinum, mixed in some instances with tiny 

 pebbles and silt (Zenkovich, 1937; Tomilin, 1954).'^ 



It may be concluded too from this bathymetric survey that there can be no mass descent of the krill 

 in winter from the mainly north-west-flowing Antarctic surface water into the mainly south-east- 

 flowing warm deep water, a descent such as for instance Ommanney (1936) and Mackintosh (1937) 

 have shown is annually undertaken by Rhincalanus gigas, Eukrohnia hamata and Calanus acuttis and 

 is to be supposed as Mackintosh remarks to result in a large scale circulation whereby these important 

 Antarctic species continue to maintain themselves within the limits of their normal distribution, their 

 wintering in the counter-flowing deep current compensating for their northward drift at the surface. 

 For as Table 35 shows, whatever the season of the year, and least of all in winter and spring, the 

 older stages of the whale food are not encountered below 250 m., that is to say in the warm core of 

 the deep current, except in negligible numbers. And even these it seems (p. 160), or at any rate some 

 of them, might well have been captured at higher levels. 



Table 35. Seasonal abundance of staple ivhale food at depths below 250 m. 



Spring Summer Autumn Winter 



(Sept.-Nov.) {Dec.-Feb.) {March-May) (June-Aug.) 



Total Number Average Total Number Average Total Number Average Total Number Average 

 catch of hauls per haul catch of hauls per haul catch of hauls per haul catch of hauls per haul 



72 70 I 529 III 4 494 98 5 31 30 I 



Even supposing this species did in fact make a mass annual descent into the counter-flowing deep 

 current the obvious question would arise as to what, it being a voracious herbivore, it would find to 

 eat. It might not of course require to eat, or could exist on very little, but if it required to feed sub- 

 stantially it seems doubtful if the rain of dead or dying phytoplankton from above would be enough 

 to maintain it, unless it should prove (p. 355, note 2) to be a carnivore then. 



That the krill should be concentrated, as they manifestly are, so close to the surface is perhaps not 

 after all very surprising when one considers that it is there, where the light intensity is strongest, 

 that the diatoms on which they live are themselves most heavily massed. In northern European 

 waters Gran (1912) concluded that 'the light optimum for far the greater part, if not for all, of our 

 assimilating plankton algae is situated close to the surface, probably not as deep as 10 m., and we 

 might perhaps even venture the assertion, that algae occurring in our latitudes with maximum 

 deeper than 30 m. have never any optimum of development down here, but are in a relatively stag- 

 nating period of life, either because they are removed from their true home, or because they have their 

 period of growth at another season'. 



In conclusion, it may be observed, the foregoing takes no account of the ' escape factor ' (pp. 258-68) 

 involved when sampling the surface layer, a factor operating by night as well as by day. If it were 

 possible to put a figure for this, the sudden decline in density that has been shown to occur im- 

 mediately below the surface would manifestly be revealed as a far more striking phenomenon than 

 our nets are able to show. 



1 Andrews (1909, 1916); Ingebrigsten (1929); Hjort (1933); Gunther (1949); Nemoto (1957, 1959) et al. 

 ^ Among the large Cetacea as a whole the sperm whale is probably the only other species that on occasion visits the bottom 

 to take demersal animals (Clarke, 1956). 



18 DM 



