Oceanic pelagic prey of benthopelagic fish in the benthic boundary layer of a marginal oceanic region

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 at depths on the slope corresponding to the daytime depths of the pelagic prey. The occurrence of these pelagic species at the benthic boundary layer is primarily through truncation of their pelagic vertical distributions rather than horizontal impingement, although this does occur: this applies not only to epi- and mesopelagic but also to the bathypelagic species which can even reach abyssal sediments. Diel 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 up the contours of the slope sediment.