Winter distribution and condition of Antarctic krill in relation to sea-ice and water column production in the South Shetland Islands during Austral Winter 2013

Acoustic and net sampling of Antarctic Krill and other euphausiids was conducted at 88 stations around the South Shetland Islands during a 30 day cruise between 10 August and 9 September 2013. Abundance and demographic patterns revealed that Antarctic krill were concentrated in the southern Bransfield Strait, and that these krill were approximately 33mm in length, about 10mm larger than found during the 2012 winter survey (Reiss and Jones 2013; WG-EMM 13/40) but similar in size to krill found in the German survey during summer in 2013 (Siegel 2013; WG-EMM 13/24). Large krill (>50mm), although present around Elephant Island, were not abundant in any area, and were also not abundant in the water column between 170 and 650m depth in the Antarctic Circumpolar Current. Sea ice extent and concentration was expansive (north of 60 S around Elephant Island) and the sea ice concentration was mostly more than 50%. Observations of birds and mammals showed that many species were found in southwestern Bransfield Strait, associated with the high concentrations of krill, an area targeted by the krill fishery in recent years. Species of note included Crabeater seals, Antarctic fur seal (sub-Adults), Leopard seal, and Adelie penguins. The high abundance of predators and prey in the Bransfield Strait, where the krill fishery is prosecuted into autumn, suggests that overlap between krill dependent predators and the fishery extends throughout the post reproductive period of many higher predators. Such overlap could impact the overwinter survival of predators if the fishery extracts prey from hotspots during autumn.