Distribution and density of Antarctic krill (Euphausia superba) and ice krill (E. crystallorophias) off Adélie Land in austral summer 2008 estimated by acoustical methods

From January to February 2008 the training research vessel TRV Umitaka Maru conducted a comprehensive oceanographic survey of the waters around the 140°E meridian off Adélie Land as part of the Collaborative East Antarctic Marine Census (CEAMARC) project. The acoustic component of this survey was conducted using a scientific echosounder operating at 38 and 70 kHz to estimate the distribution and density of Antarctic krill (Euphausia superba) and ice krill (E. crystallorophias). In addition, the relationship between the vertical distribution of Antarctic krill and the water temperature structure along the 140°E meridian was investigated. Antarctic krill were distributed in the waters of the continental slope at 65–66°S and the maximum value of the mean areal density ρ in 1 nautical mile (nmi) intervals was 4344 inds. m−2. Ice krill were distributed in the neritic waters of the continental shelf to the south of the 66°S and the maximum ρ in 1 nmi intervals was 23,669 inds. m−2. Along the 140°E meridian, Antarctic krill were mainly distributed at the water temperatures below 0.5 °C. Although they were mostly distributed shallower than approximately 100 m, dense aggregations at approximately 180–200 m were also observed, which coincided with a depression of the water temperature structure.