Behavioural differences in relation to pycnoclines during vertical migration of the euphausiids Meganyctiphanes norvegica (M. Sars) and Thysanoessa raschii (M. Sars)

An observation on differences in the vertical migration patternbetween Meganyctiphanes norvegica (M. Sars) and Thysanoessaraschii (M. Sars) caused by the presence of a thermocline isreported. Generally, M.norvegica did not migrate through a thermoclineat 50–60 m depth while T.raschii did. This observationis discussed in the context of how the combination of differencesin vertical migration and advection over sill depth may affectthe abundance of fjord stocks of these two euphausiid species.