Observations on the ecology of deep-sea bottom-living fishes collected off northwest Africa (08°–27°N)

The ecology of bottom-living fishes was investigated from a series of collections off northwest Africa in the area 08°–27°N and 14°–30°W from sounding of 261–6059 m. The variety of sampling gear included epibenthic sledges, a semi-balloon otter trawl, benthic traps and longlines. A total of 92 operations collected more than 4600 specimens of at least 148 species. The catches of both types towed gear were shown to have a high degree of similarity, but sampled a different spectrum of species to the static baited gears. An overall consistency by latitude was found in the composition of the net catches. Despite possible indications of faunal boundaries at around 1100 m and 2100 m, the salient feature of an analysis of catch composition by sounding was the generally steady faunal change to a depth of about 3000 m. The only obvious discontinuity was evident at this level, beyond which the fish fauna was more uniform. This lack of marked species assemblages, characteristic of other regions, may result from the high primary productivity in the area. Features distinguishing the fish fauna of the area from that of the non-upwelling temperate western North Atlantic were found to be the smaller mean size of the dominant species, the abundance of bathygadine macrourids and the evident lack of the ‘bigger-deeper’ phenomenon. The relative density of fishes was estimated and shown to decrease by 2 orders of magnitude from the upper slope to 2000 m soundings. Below this the decline was less marked and relative densities of around 0.5 fish/1000 m² were maintained to at least 4000 m soundings.The abundance of slope fishes in the area was tentatively estimated to be greater than in the non-upwelling temperate western North Atlantic. Few species were abundant; only 25% were represented by more than 17 specimens. Yet the dominant family, the Macrouridae, was represented by 48% of the specimens and 18%of the species. A total of 14 species from 6 families, represented by 60 or more specimens, were examined in detail to provide information on vertical distribution, population structure, breeding biology and feeding. Niche availability and resource partitioning among co-occurring species of macrourids are briefly discussed. Station and species data are given, together with a note on the likely conspecificity of Coryphaenoides colon with C. zaniophorus.