Split-beam target tracking can be used to study the swimming behaviour of deep-living plankton in situ

A scattering layer consisting mainly of krill (Meganyctiphanes norvegica) was studied with a submersible transducer, to assess the behaviour of individual organisms in Situ by means of split-beam target tracking. Individuals were resolved and tracked, but a rapid increase in average swimming speeds with depth suggested that inaccuracies in the angular estimates affected the estimates. Attempts were made to smooth the tracks during post-processing. Smoothed speeds suggested that most (>78%) invertebrates swam at speeds below 12 cm s(-1) (mode similar to4 cm s(-1)), with components of speed larger in the horizontal plane than in the vertical. (C) 2003 Editions scientifiques et medicales Elsevier SAS and Ifremer/IRD/Inra/Cernagref. All rights reserved.