Population structure of daytime surface swarms of the euphausiid Meganyctiphanes norvegica in the Bay of Fundy

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Abstract
Daytime surface swarms of the euphausiid M. norvegica occurring off Brier and Long Islands in the Bay of Fundy were studied during the summers of 1979-1983. Individual swarms had highly skewed sex ratios; both male dominated and female dominated swarms were encountered but female swarms were more common. Individuals in surface swarms comprised a restricted part of the population when compared to samples taken at depth and when compared to the population structure of this species at similar times of year in other studies. Both males and females were in breeding condition; males possessed ripe spermatophores, females were fertilized and exhibited ovaries in an advanced stage of maturation. The presence of swarms was accompanied by bursts of M. norvegica eggs in the plankton on spatial and temporal scales coincident with the swarming events. These swarms apparently are related to reproductive activity.