In situ lander observations of deep-sea fishes in the eastern Atlantic ocean
For the first time autonomous free-fall vehicles (AUDOS/ROBIO) were deployed at low latitudes in the northeast Atlantic, south of a proposed faunal divide at 40°N with a high abundance of large species of rattails to the north and lower biomass of smaller fish species to the south (Merrett 1987). Observations of deep demersal fishes attracted to baited cameras were made at four stations near upwelling areas off West Africa: Canaries (27°20’N; 16°59’W), Cape Verde Terrace (17°45’N; 20°30’W), Cape Verde Abyssal Plain (15°N; 20°30’W) and the Angola Slope (7°45’S; 5°59’E). The Canaries/Cape Verde study revealed a high abundance of large Coryphaenoides (Nematonurus) armatus at 17°N and Angola showed the highest fish biodiversity of all baited camera lander work in the eastern Atlantic Ocean, with a minimum of 9 species observed. These are violations of this putative zoogeographic divide at 40°N. The first observations on the swimming behaviour of the ophidiid Barathrites iris are reported, revealing a mean speed of 0.2135m.s-1 at 4000m in the Cape Verde Abyssal Plain compared to 0.15347m.s-1 for the grenadier C. (N.) armatus at the same site. Swimming speeds of Antimora rostrata and C. (N.) armatus recorded during autumn (Sep/Oct) and spring (Mar/Apr) revealed elevated fish activity in the autumn season, following the summer months characterised by a higher flux of particulate organic matter to the benthos. It is suggested that seasonal enrichment to the benthos and fall-out from high surface productivity in upwelling regions are associated with increased levels of fish activity and sustain the abundant deep-sea fish assemblages documented in this study.