112 DISCOVERY REPORTS 



1400 hr., this movement does not it seems involve a very significant part of the total surface 

 population.' 



It is distinctly possible too that even the minor to moderate daylight gatherings we have recorded 

 in the 500-250 m. layer and deeper may in many instances have come from a higher level, there being 

 some doubt about some of the early vertical horizons recorded in R.R.S. 'Discovery' and R.R.S. 

 'William Scoresby'. Both vessels had to be laid beam on to wind and sea on station and in con- 

 sequence were inclined to make so much leeway, their wires straying far from the vertical, that many 

 of the nets they fished, more especially in the stronger winds, must in fact have been sampling higher 

 levels than they are reputed to have done. The old 'Discovery' (Chaplin, 1932), with her massive hull 

 and clutter of rigging, was particularly liable to drift, ^ and ' Scoresby ' too on station sometimes made 

 leeway at quite astonishing speed. I recall one occasion in the Bransfield Strait particularly vividly when 

 she must have been moving bodily to leeward at a rate of at least 2 knots. Here, at Station WS 391, we 

 were working vertical nets in a 30 knot (Force 7) wind and our wires were straying far out to weather 

 at an angle that seemed to be over 45°. Our leeway in fact was so great that I decided to tow the 

 oblique (loo-o m.) nets without the engines as we drove bodily before the gale. The usual 200 m. of 

 warp was paid away with a 56 lb. streamlined lead and bar, one stramin net on its heavy ring and one 

 70-cm. diameter silk net attached by their closing apparatus, at the end. Yet with all this massive 

 clutter of gear on its heavy warp the nets at their deepest scarcely touched 120 m. I therefore conclude 

 that the Calyptopes taken in the much less weighty 500-250 m. vertical net between 0200 and 0600 hr. 

 on this occasion must in fact have come from a higher level. I think, too, that the 480 early Furcilias 

 recorded by Eraser in the 250-100 m. net fished between 0600 and 1000 hr. at Station WS 527 

 (Fig. 11), with the ship drifting bodily to leeward before a 20-knot breeze, could also have come 

 from nearer the surface. On the same grounds the accuracy of some of the early vertical horizons 

 recorded in R.R.S. 'Discovery II ', before her then Commander, the late W. M. Carey, R.N. (Retd.), 

 successfully laid her head on to wind on station, is also open to doubt.^ 



I feel, therefore, it must be not a little significant that so many of the larvae we have recorded as 

 having apparently migrated from the surface down into the warm deep layer below 250 m. (see 

 bracketed numbers in catch-tables for Figs. 9 and 11) should have been taken from drifting vessels 

 moving steadily along before winds of force 4-5 (15-21 knots) or over. 



It follows from the foregoing that of the two broadly distinguishable larval communities in the sea, 

 the climbers and those with the ascent accomplished, the latter, as Professor Ruud (p. 44) recognised 

 so long ago, are essentially creatures of the Antarctic surface layer, and that there as they grow, 

 especially as Furcilias, their vertical movements become confined to an increasingly narrow stratum 

 so that they tend more and more readily to get carried along in the surface stream. The pronounced 

 and steady decline in total numbers of larvae* taken below 250 m. as development proceeds (Table 21) 

 provides further evidence of the lessening range of their vertical movements as they grow. Mortality 

 it is true may also be contributing to the decline, but I do not believe it to be the overriding factor. 



In terms of average numbers taken per 250 m. haul, the vertical distribution of the total free popula- 

 tion of grouped Calyptopes and Furcilias works out for daylight and darkness as in Table 22 where 

 {a) shows the average gatherings based on all stations, both positive and negative, made during the 



* Reproductions of Eraser's Fig. 72, showing the pronounced diurnal vertical movement of his Calyptopes, appear in 

 Gushing (1951), Zimmer (1956) and Nicol (i960). 



* Striking illustrations of how her plankton, hydrological and sounding wires used to drag out to windward, even in 

 moderate weather, are given by Gunther (1928). 



^ This, however, applies only to the first twenty of the grand total of 1320 odd vertical net stations she made during her 

 long career in southern waters. 



* Excluding of course the still climbing First Calyptopes. 



