An assessment of the biological and acoustic characteristics of swarms of Antarctic krill

Measurements on krill from distinct swarms and echo-sounder measurements of the same swarms have been analysed using multivariate methods. The analysis has addressed the problems of whether krill swarms in a small area may be of a limited number of types, and whether the biological characteristics of the krill could be related to the echo-sounder measurements of the swarm. The main sources of biological variation between krill in different swarms seemed to be related to size and maturity. Krill swarms did not appear to form groups based on biological similarity, and swarms caught in the same haul were as different as swarms caught in different hauls. However, swarms could be divided into groups on the basis of time of day and swarm depth. The biological features (size, maturity, sex ratio and moult stage) of krill in the swarms were not related to echo-sounder observations (horizontal and vertical extent, depth and density of swarms), although some degree of separation between swarms containing large and small krill may be possible if the shape of the swarms is considered. Information on biological characteristics of krill in swarms must still be collected using nets.