Acoustic monitoring and evaluation of krill in the Antarctic ecosystem Bransfield Strait and around Elephant Island during ANTAR XXI and XXII, aboard RV Humboldt, Peru

Monitoring and hydroacoustic assessment of the distribution and biomass of krill (Euphausia superba) was held on board the BIC Humboldt during scientific campaigns Peru to Antarctica in the austral summer: Antar XXI (15 to 22 February 2013) and Antar XXII (22 to 31 January 2014). The areas included Bransfield Strait, Joinville and around Elephant Island (Antar XXI: : 8 040 nm2 with 10 transects; ANTAR XXII: 21 070.62 nm2 with 17 transects) .The SIMRAD EK60 scientific echosounder used for multifrequency 120 and 38 kHz, respectively. This system is calibrated according to the procedure of ICES. For pelagic trawl hauls- Pelagic Engel gear were used for checking acoustic signals (Antar XXI: 9 stations; ANTAR XXII: 16 stations). Results indicated that krill swarms during the day swarms were recorded at high densities between 20 and 50 m deep while overnight, dispersed and scattered swarms were detected from the surface to 20 m deep. A wide distribution of krill in the study area, the highest densities (> 1000 m / mn²) were observed around Elephant Island and Joinville was recorded; while the lowest were recorded in the Bransfield Strait and between Deception Island and Isla Torre (250-1 000 m / mn²). The estimations of hydroacoustic biomass krill by the method of Distorted Stochastic Approximation Wave (SDWBA) were 876.367 t and t 7'330,574 during ANTAR XXI and XXII respectively. The estimated biomass in Elephant Island (4'569,039 t) represents 62.3% of all existing biomass in the study area.