Distribution, abundance and spatial proximity swarms of krill (Euphausia superba) along Bransfield strait and Elephant Island, austral summer 2006

Abstract

It has been performed a synoptic acoustic survey aboard RV Humboldt along Bransfield Strait and surroundings of Elephant Island, and a small scale experiment between Elephant, Clarence and Gibbs islands during austral summer 2006 in order to assess the distribution, abundance and spatial proximity of swarms of krill (Euphausia superba) in relation to its predators. Main results were: (i) abundance of krill along Bransfield Strait and surroundings of Elephant Island is the lowest value of the time series built up by Instituto del Mar del Perú (IMARPE) since 1988. It has been calculated an abundance of 425 thousand tons of krill (CV: 35%) under the hypothesis that the observed relative absence of ice has confined the krill population toward the Antarctic Peninsula, out of reach of the survey, (ii) it has been observed that the distribution of krill would drag the local presence of its predators by observing the synchronous variations in the location of sea birds and mammals in every of the nine gyres performed over a small area (18 mn2) located between Elephant, Clarence and Gibbs islands, (iii) the ascent of krill toward sea surface implies a temporal reduction of its acoustic reflectivity, which would confirm that swimming angle during vertical migrations explains the measured variations of backscattered energy between diel cycles. Nevertheless it is concluded that these findings must be validated by new experiments to be performed on wider geographical ranges