Vertical distribution and diel vertical migration of krill beneath snow-covered ice and in ice-free waters.

摘要: A bottom mounted upward looking Simrad EK60 120-kHz echo sounder was used to study scattering layers (SLs) and individuals of the krill Meganyctiphanes norvegica. The mooring situated at 150-m depth in Oslofjord, connected with an onshore cable for power transmission digitized data. Records spanned 5 months from late autumn spring. current meter CTD associated acoustic a shore-based webcam monitored ice conditions fjord. continuous measurements were supplemented intermittent sampling campaigns their physical biological environment. carried out diel vertical migration (DVM) throughout winter, regardless distribution potential prey. fjord froze over mid-winter daytime mid-water SL immediately became shallower snow fall after freezing, likely related reduction light intensities. Still, fraction population always descended all way bottom, so that by day seemed inhabit waters levels spanning up six orders magnitude. Deep-living ascended synchrony rest afternoon, but consistently reappeared near-bottom already <1 h ascent. Thereafter, appeared undertake asynchronous migrations, some being present even though entire DVM.