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SynopsisAnalyses of winter and summer vertical migrations of Meganyctiphanes norvegica are given and the differences in behaviour pointed out. A vertical layering of size classes, larger specimens occurring deeper than smaller ones, is shown to exist during the day and night.Four potential methods of feeding were found. The inter-relationships between vertical migration, feeding method used, and type of food eaten are discussed.The relationship of carapace length to total length was found to depend on the state of maturity of M. norvegica.M. norvegica matures at the age of 1 year, transference of the spermatophores taking place in January-February, the eggs being laid in March-April. The larvae take 2–3 months to reach adolescence and little growth in size takes place in the winter when the gonads are maturing. An age of 3 years may be attained but most only survive 1½—2 years.The distribution within the Clyde Sea throughout the year is described. Most of the population were found to move to the North-east Arran Area for egg-laying.A 24-hr. and annual periodicity of luminescence is described and correlated with the period of swarming of this species prior to spermatophore transference.

The availability of oceanic plankton and micronekton to the benthopelagic fish assemblages on the slopes of the Rockall Trough, a marginal region of the northeast Atlantic deep-sea environment, is examined. The vertical distribution of pelagic species predated by the fish was determined in the off-slope water column, as were the depths at which they are predated by the fish in the benthic boundary layer of the slope. The benthopelagic fish predated pelagic species a t depths on thta slope corresponding to the daytime depths of the pelagic prey. The occurrence of these pelagic species a t the benthic boundary layer is primarily through truncation of their pelagic vertical distributions rather than horizontal impingement, although this does occur: thls applies not only to epi-and mesopelagic but also to the bathypelagic species which can even reach abyssal sediments. Die1 vertical migration of the pelagic species did not make them available to slope fishes in shallower depths presumably because vertical migration is strictly upwards within the pelagic water column and not u p the contours of the slope sediment.

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