Variations in the size of Antarctic krill, Euphausia superba Dana, in small swarms

Studies on the characteristics of krill in individual swarms require sampling methods which ensure that the swarms are sampled discretely.A study on the size composition of krill swarms using an enlarged Longhurst-Hardy plankton recorder (LLHPR) and an echosounder reveal that the length frequency distnbutions of krill in adjacent swarnls were often significantly different.In contrast, length frequency distnbutions from within the same swarm were not usually significantly different and any differences were probably caused by several swarms overlapping in the LLHPR samples.The size of krill in the samples showed as much variation over short d~stances (several hundred metres) as over longer distances (several kilometres).Differences in size between adjacent swarms are probably due to a length-dependent sorting mechanism that restricts the size range of krill in the swarm.The presence of a few adults in many juvenile swarms indicate that this mechanism does not always operate.