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Large Raisings of the ocean bed: brief history of fish-finding researches
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Our colleagues:
After World War II the domestic industrial fishery was developed as the oceanic one. In 1947, the expeditionary prospecting and searching activities began in the Greenland and Norwegian seas aiming at the development fish-growning concentrations of the Atlantic-Scandinavian herring. By the end of the 1960s of the last century practically all shallow-water regions of the Atlantic Ocean, including the shelf of Argentina and of the South African Republic were explored by fish-finding vessels. In the late 1960s – early 1970s many coastal states began to introduce the 200-mile economic zones. As the result, some productive regions of the Atlantic Ocean were lost for the USSR's fleet (particularly, the high-productive region in South-West Atlantic). It was necessary to compensate to some extent the reduction of the total catch. The efforts of looking for the productive areas were made outside the 200-mile zones.
While planning and organizing the research activities, great attention was paid to the raisings of the Atlantic Ocean bed, first of all, in the area of the Mid-Atlantic Ridge. In 1973, the Zaprybpromrazvedka organized an expedition. The main purpose was looking for some new objects and regions within the limits of the North-Atlantic ridge and of the Reykjanes Ridge. As the result of the prospecting activities at the comb zone of these ridges to the north from 49 – 50 E large stocks of the Rat-tail (Coryphaenoides rupestris) were discovered. Six seamounts, unknown before, were discovered; the hydrographic survey was executed and the large-scale (1:50000) bathymetric maps of these seamounts were made.
Later (in the 1970s – 1980s) the research activities within the limits of the Mid-Atlantic Ridge were continued. As a result, the fishing potential of already known seamounts (Great Meteor, Plato, Cheuser and others) were researched and many unknown seamounts were discovered in the North and the South Atlantic. Particularly, the fish stocks of Alfoncinos redsnappers (Beryx splendens), Horse mackerel (Trachurus trachurus), Atlanticn mackerel (Scomber scombrus) were found on some seamounts of the North Atlantic Ridge.
The large scale geologic-geomorphological researchers, executed in the Mid-Atlantic Ridge, allowed to update a constitution of its comb zone substantially revealed and observe the direction of main lineaments, variously-aged and different-scale breaking crustul disturbances in the area of the given morphostructure.
The research activities and fishery on the seamounts of the Mid-Atlantic Ridge have shown the following:
1. Despite of rather large quantity of the seamounts in the ridge, the total fishing area is rather small.
2. The stocks of the fishery objects in the zone of the Mid-Atlantic Ridge are rather insignificant.
3. The fishery on the seamounts of the Mid-Atlantic Ridge comb zone is inconvenenient due to the very complicated relief and poor level scrutiny of the hydrodynamic conditions in the fishery regions.
Considering all this, it was decided to study the fishing potential of other raisings of the Atlantic bottom (first of all so-called aseismic raisings). In 1976, the Zaprybpromrazvedka authorities organized two research expeditions to the Angular raising and the Whale ridge. As the result of these researches the fish stocks of Alfoncinos redsnappers, Rudderfish (Hyperoglyphe spp.), Boarfish (Pentaceros richardsoni), Redbait (Emmelichthy Richardson), Dolkfish (Trichirus spp.) were found. During the of expeditions the unknown before seamounts were found. For all of them the detailed large-scale bathymetric maps were made.
The fish stocks of valuable fish detected within the Whale ridge and Angular raising testified that many large seamounts and aseismic raisings of the ocean bed definitely have a fishery resource potential. Therefore, in the 80s the research efforts of the Zaprybpromrazvedka and the AtlantNIRO were directed towards the analysis of aseismic raisings: the elevations Riu-Grandi, Modes, Sierra-Leone, Guinean, Cap raisings, the large seamounts in Madeira-Canary region. Since 1973 till 1991. More than 200 seamounts were studied in the Atlantic during 360 scientific-research expeditions of the Zaprybpromrazvedka. The large-scale bathymetric maps were made for 149 of them, for 83 seamounts in North Atlantic and for 66 seamounts in South Atlantic.
In 1978 – 1980, the research expeditions of the Zaprybpromrazvedka and the AtlantNIRO found large stocks of Horse mackerel (Trachurus symmetricus murphyi) outside the 200-mile zones of Peru and Chile. The aseismic raisings of South-East Pacific – ridges Naska, Sala-and-Gomes, Chilean raising were studied during this period. The fishable concentrations of Horse mackerel, Alfoncinos redsnappers, Pacific mackerel (Scomber japonicus), Redbait (южной – Emmelichthys nitidus and pink – Emmelichthys struhsakerl) и Lobster were discovered. Since 1978 till 1991 the large scale of the hydrographic work was made in the South-East part of the Pacific Ocean. During 112 voyages of the research ships. 30 unknown seamounts were found in this part of the Pacific, detailed maps with 1:50000 scale were made for 28 of them, and a bathymetric map (with 1:500000 scale) was made for the whole Naska Ridge.
The executed hydrographic work (measurement, compiling of the large-scale bathymetric maps) promoted the prompt development of biological resources of the Mid-Atlantic Ridge, aseismic raisings of the Atlantic and Pacific oceans, as well as the reduction of an accident rate of drag activities.
The research on aseismic raisings showed that despite of great morphological and structural differences they had a lot in common.
1. All aseismic raisings brand large fractures (zone of fractures), which as a rule do not coincide with transversal faults of the Mid-ocean ridges.
2. Aseismic raisings are represented by many morphostructural types: the micro continents, the block, the block-volcanic, the volcanic raisings and ridges, chains of volcanic mounts, of a different size and configuration.
3. All aseismic raisings have a block structure. The crustul blocks in the aseismic raisings lay at different plutonic levels.
4. The large aseismic raisings are quite often crowned with thick series of carbonate deposits. They point to a shallow-water stage in development of these formations.
5. Large aseismic raisings (Naska, Whale Ridge) have an asymmetrical tranverse bench section.
6. Many aseismic raisings have leveled summit plains and terraced slopes, which points to subaerial phase of their development and testifies about eustatic changes in ocean levels or differentiated vertical tectonics of these structures.
All those years during various expeditions, which explored the seamounts of the Mid-Atlantic Ridge, East Pacific raisings and many aseismic raisings of the Atlantic and Pacific oceans, the stuff of the marine geology (fishery hydrographic) department, who are high-qualified specialists, fruitfully labored. They were hydrography engineers, geomorphologists, geologists A.A. Demidov, N.N. Deryabin, L.A. Zakharov, I.A. Rubin, A.V. Soldatov, V.E. Timkin, V.T. Matsegora, A.S. Melnichuk. In many respects, due to their researches the bathymetric maps of the Atlantic and Pacific seamounts were made.
At first, the seamounts, discovered in the Atlantic and Pacific oceans, got the names of the ships, that found them: the "Blesk", the "Vaida", the "Stvor" (Atlantic). Later they were named after the famous scientists (the "Academik Knipovich", the "Mesyatsev" – Atlantic; the "Panov", the "Shorigin", the "Marti", the "Zernov", the "Dorofeev", the "Markov", the "Strakhov" and others – the Pacific ocean) or by the names of people, who contributed a lot in discovering the biological resources of the World ocean (the "Kapitan Demidov", the "Probatov", the "Belobrov", the "Faleev", the "Churov", the "Travin", the "Gololobov" and others – Atlantic; the "Zasosov", the "Baral", the "Boris Karasyov" and others – the Pacific ocean). These names are approved by the Interdepartmental commission for the geographic titles in the Academy of Science of the USSR.
Thus, the fisheries research in the 1970s – 1980s showed, that some particular parts of the Mid-Atlantic Ridge as well as the parts of aseismic raisings in the Atlantic and Pacific oceans had high bioproductivity. Quite often the large raisings of the ocean bed cause the loci of high bioproductivity. However, as a rule, the biomasses of fish stocks on the seamounts of the Mid-Atlantic Ridge and of aseismic raisings are not too extensive. Therefore, the fishery in these regions must be strictly regulated. Unattended and uncontrolled fishing can result in destruction of those fish stocks. During the summer of 1976, the intensive fishery haul of Alfoncinos redsnappers on the seamounts of the Angular raising caused practically total destruction of this valuable fish. The stocks of Alfoncinos redsnappers here were partially restored only in the mid 1990s. After rather active exploitation of fishable concentrations of Redbait on the ridges of Naska and Sala-and-Gomes in January – in February of 1979 the stocks of these fishes had not restored until 1991.
Therefore, a great effort, made by the international organizations, which regulate fishing in any regions of the World Ocean, is required for the organization for effective and rational fishery on the seamounts of the Mid-ocean ridges and aseismic raisings.
The Mid-ocean ridges and aseismic raisings take about 27 % of the World Ocean bed. Some geomorphology and fishery objects are still poorly studied. Undoubtedly, further researches of these morphostructures would allow not only to update their constitution but also would discover new productive areas of the ocean.
