Distribution of krill between South Georgia and Bouvet Island in the Southern Ocean

CapturaMaster thesis from the University of Oslo, Norway, Department of Biology, Faculty of Mathematics and Natural Science.

A 2009 thesis by Dag Lennart Nielsen which analyzed large and small-scale distribution of krill (Euphausia superba) between South Georgia and Bouvet Island in the Southern Ocean.

This work is in line with current CCAMLR activities to balance preservation and commercial activities.

The abundance and distribution of Antarctic krill is poorly known for some parts of the Southern Ocean. Enhanced interest in krill fisheries highlights the need for precise and reliable data to secure the population through international agreements.

The acoustic survey AKES 1 (Acoustic Krill Estimation Survey) made by IMR (Institute for Marine Research, Norway) was conducted in the Southern Ocean between South Georgia and Bouvet Island, during January and February 2008. Waters around South Georgia, the Open Sea region between South Georgia and Bouvet, and the area close to Bouvet Island were investigated where limited knowledge on krill distribution in the two last areas is a norm.

The abundance of the Antarctic krill was studied and South Antarctic krill was the prevailing organism in the water column.

Krill aggregations had larger size and density close to South Georgia and Bouvet Island, compared with the Open Sea. At South Georgia aggregations were over all larger than in the two other areas, and this was the region with the highest krill abundance per surface area. The largest single aggregations of krill were found at Bouvet Island, though few in numbers. The Open Sea area hold few and small aggregations compared to the volume sampled, even in cold waters south of the Polar Front. The krill were more or less absent close to, and north of the Polar Front.

The higher abundance of krill close to the two islands coincided with intermediate chlorophyll a levels, known to be one of the factors contributing to preferable krill habitats.

In the Open Sea south of the Polar Front, krill often occurred in a continuous low- density belt in the upper 60m of the water column during night. At daytime krill formed small aggregations with a peak around 40-60m depth, with densities higher than what could be found in the diffuse belt at night.

At Bouvet Island krill aggregated close to the surface in dense compact swarms during night and at daytime krill formed both small swarms with a low density and some large aggregations between 20-80m depth.

See full thesis at Large and small-scale distribution of krill (Euphausia superba) between South Georgia and Bouvet Island in the Southern Ocean