1. Main Results of Russian Fisheries Underwater Research in the Mid-Atlantic Ridge Region Mikhail L. Zaferman* and Alexei M. Orlov** *- Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO), Murmansk, Russia. zaferman@pinro.ruzaferman@pinro.ru ** - Russian Federal Research Institute of Fisheries and Oceanography (VNIRO), Moscow, Russia. orlov@vniro.ruorlov@vniro.ru BACKGROUND. A biological diversity of the thalasso-bathyal fauna is now still insufficiently known, especially on the mid-ocean ridges and regarding to fisheries. The main reasons are the great remoteness of these regions, great depths, complicated nature of the bottom relief and currents, as well as low effectiveness of usage the traditional trawl and acoustical methods under these conditions. Manned submersibles which present a new methodological approach to underwater objects studying give the opportunity to carry out some fisheries investigations which can not be done by means of traditional methods, and to receive new data in principle. These investigations include: - investigations of the water animals biotope (bottom topography, ground patterns, water transparency and colour, currents, plankton, benthos, ichthyofauna) and their relationships; - studies of the features of spatial and vertical distribution of the hydrobionts; - investigations of the animal behaviour under natural conditions. - analysis of the behaviuoral responses to fishing gears, examination of the trawl efficiency; - determination of the length composition of water animals in situ and their aggregations density; - decoding of echograms and acoustical survey devices calibration in the density units; The use of submersibles complete with traditional means by the complementary principle is the most effective one. It gives the opportunity, on the one hand, to solve some problems of traditional methods, and on the other hand, to extend the scope of underwater observation data to the wide areas. In this connection, the underwater research of natural and anthropogenic fish behaviour are of great importance, as these data give an opportunity to know fine mechanisms of fishing processes, migrations, commercial aggregations forming, etc. MATERIALS. Three research expedition by PINRO in 1983, 1986, and 1988 on the research ships “Odyssey” and “Ichthyandr” have inspected about 40 underwater mountains in the regions of Mid-Atlantic Ridge and adjacent areas of the North Atlantic by means of the manned submersible “Sever-2” (max. depth 2 km, crew 5 persons). During these expeditions 71 dives were done up to depths of 2000 m, total time underwater was about 500 h, total path traveled by submersible was about 350 nautical miles. Subjects of inquiry were: bottom and bentho-pelagic fish (roundnose grenadier, tusk, orange roughy, northern wolffish, redfish, deepwater sharks, polyprion etc.), bottom invertebrates (deepwater red crab, shrimps), pelagic species (redfish, lantern fish, squids), as well as their environment (underwater landscapes, bottom currents, forage objects). MAIN RESULTS. The following main results were achieved: The data on micro- and mesorelief and natural conditions of bottom landscapes on underwater mountains were received. The strong tidal currents of alternating speed and direction were found within the thin near-bottom layer where they can not be determine by standard methods. The composition and distribution of ichthyofauna on underwater mountains were studied. Dense aggregations of roundnose grenadier were found at underwater canyons and depressions of bottom relief, as well as other fish species which are of commercial interest but could not be revealed from the sea surface. These data were confirmed by experimental deepwater longlining. Roundnose grenadier prefers quiet places but can resist to strong bottom currents. At that it reveals an optomotor reaction in spite of absence of light at the depths. The calculation showed that the weak Cerenkov light radiation from radioactive decay of the potassium isotope in sea water may be sufficient for the eyesight of grenadier (and other deepwater fishes having big eyes). Sub-daily vertical migrations of roundnose grenadier take place in tidal rhythm: raise of upper edge of aggregation and dispersion during flow tide, and pressing to bottom during ebb tide. The reason may be the transference of the forage objects (squids, shrimps) by hydrodynamic eddy above the mountains during the flow tide. The data on density of mass fish and deepwater crab species at some underwater mountains were received. The results of expeditions showed the high efficiency of underwater technologies in investigations of deepwater regions of the World Ocean. Deep-sea manned submersible “Sever-2” Deep-water red crab Gerion sp. Deep-water red crab Gerion sp. Atlantic halibut Hippoglossus hippoglossus Orange roughy Hoplostethus atlanticus Orange roughy Hoplostethus atlanticus Orange roughy Hoplostethus atlanticus Redfish Sebastes mentella Redfish Sebastes mentella Roundnose grenadier Coryphaenoides rupestris: dense near-bottom aggregations The altitude of the upper edge of grenadier aggregations by underwater observations from submersible: multi-day observations at two underwater mountains on latitude 51° N and 53° N Diving sites of submersible “Sever-2” in the North Atlantic, 1983-1988 Two types of vertical distribution of grenadier: compression during the flow tide (left) and depression during the ebb tide (right)