Diel vertical migration of Antarctic krill (Euphausia superba) swarm in the Bransfield Strait during austral autumn 2016 inferred from acoustic data and its relations to environmental factors

Recently, krill fishery has concentrated increasingly in the Bransfield Strait, and krill abundance and ecological characteristics have received much attention. Antarctic krill (Euphausia superba) presents significant diel vertical migration (DVM) pattern, such studies were conducted to provide the basic data for exploring the formation mechanism of fishing ground and the reference for feedback management of krill fishery. Scientific acoustic device mounted in fishing vessels can reflect directly the distribution and vertical movement of krill in the water column. Based on the acoustic data recorded by Simrad EK 80 used in krill fishing vessel, krill swarms were identified using Echoview software.The present study analyzed DVM of krill in the Bransfield Strait during the austral autumn 2016 and the factors that impact DVM of krill were further explored. The results indicate that the depth of krill swarm maintained to above 250 m, the highest frequency of average deepest (shallowest) krill swarm occurs at sunrise (at night). The largest thickness of krill swarm presents at sunrise. Krill swarms are distributed in the deeper water column in the daytime, but move to the shallower depth at night. Compared to March, the average depth of krill swarms increased in April. Brightness and bottom depth are the main factors that impacted depth change of krill swarms.