. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. THE OLDER STAGES 167 surface from daylight to dusk (Table 34, series (a)) are simply an expression of the lessening measure of evasion that the older krill can achieve as the strength of the daylight wanes (see also p. 259, Tables 50 and 54). The large to very large catches obtained on the surface as soon as full dark- ness set in (Table 34, series (b)), obtained, it may be emphasised again, in the same v^^ater traversed by the last sbc hauls made in the waning hours of daylight before the ship
. Discovery reports. Discovery (Ship); Scientific expeditions; Ocean; Antarctica; Falkland Islands. THE OLDER STAGES 167 surface from daylight to dusk (Table 34, series (a)) are simply an expression of the lessening measure of evasion that the older krill can achieve as the strength of the daylight wanes (see also p. 259, Tables 50 and 54). The large to very large catches obtained on the surface as soon as full dark- ness set in (Table 34, series (b)), obtained, it may be emphasised again, in the same v^^ater traversed by the last sbc hauls made in the waning hours of daylight before the ship was put about, provide convincing evidence of the extent of the evasion that must have taken place during the daylight, sunset and twilight hours. Turning again to Table 33, it will be seen that it is only in full darkness, and not, as might have been expected, by day, that there seems to have been some concentration of the I o 40 70 100 250-• YOUNG SWARMS DAY 500 1000 13 3 a 6 V I 10 £ 40- g 70- 100 250 OLD SWARMS DAY 500 1000 13 3 2 6 YOUNG SWARMS NIGHT 500 _ 1000 ~l7. OLD SWARMS NIGHT 5O0 _ 1000 "?} 2 2 1500 10 40- 70 100- 250 TOTAL STOCK DAY 500 1000 13 3 2 6 I 10 S 70 100 250 TOTAL STOCK NIGHT 500 _ 1000 7J 2 2 Fig. 18. Diumal vertical distribution of the 10 and 22 month old swarms sampled at St. 1835, the number of surface and subsurface net hauls made in dayUght and darkness being shown as in Fig. 17. krill at depths immediately below the surface, ^ such concentration as was recorded, however, decreasing rapidly below the 20 m. level and virtually disappearing it seems at about 50 m. The complete subsurface void, however, encountered between 50 and 10 m. from sunset to dusk again places the reliability of these night subsurface samplings in some considerable measure of doubt, a critical assessment of their value again having to take account of the obvious difficulty of sending an open net through a dense surface population to a deeper level and ensuring that in t
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