Deep-Water Crustacea of the Genus Sergestes (Decapoda, Natantia) from Cook Strait, New Zealand
S. arcticus has been taken in nearly every bathypelagic haul made in Cook Strait between 50 and 600 fms. However, as all nets used have been of the "open" type, specimens could have been taken at any depth between the surface and that at which the net was being used. Only four collections (V.U.Z. 25, 52, 53, 84) contain sufficient numbers of specimens to warrant individual discussion. The two most interesting were both made shortly before midnight at about 100 fms., a total of 34 specimens being taken for 2½ hours work. A haul made shortly after 1 a.m. at about 300 fms. took 7 specimens, while another made at 400 fms. after 4 p.m. caught 15 specimens.
Thus it can be said that adult S. arcticus in Cook Strait can be found during the night from at least 50 fms. to about 300 fms. with an apparent concentration at about 100 fms., while during the day there may be another concentration at about 400 fms. Sund (1920) found that during the Michael Sars North Atlantic Expedition adults were not common above about 250 fms. though they had been taken up to 100 fathoms and even less. During work with "closing" nets on the Atlantis in the Western North Atlantic, Welsh and Chace (1938) took S. arcticus between 100 and 500 fms. and later were able to show (Waterman et al, 1939) that though the centre of average vertical distribution was a little above 300 fms. extensive diurnal vertical migration of at least 100 and as much as 200 fms. takes place, some specimens being in less than 100 fms. between about 8 p.m. and 4 a.m.page 14