by
I.I. Lapitzky
Senior Scientific Worker,
Candidate of Biological Science
F o r e w o r d
No other country in the world possesses such a considerable amount of big water reservoirs on its rivers due to hydroelectric power development as does the Soviet Union.
Water reservoirs are a special kind of inland water body which differs from rivers and lakes in a number of characteristics: slower water exchange; specific physical, chemical, hydrological and temperature conditions; fish fauna and feed supply composition, and nature of water economics and fisheries. These are multipurpose water bodies which are used to a greater or lesser extent by many branches of the national economy.
In different geographical regions their utilization is based on the most suitable way of meeting the requirements arising from the economic and industrial needs of the area. For the reservoirs of the European part of the U.S.S.R. and Siberia such a typical complex includes power engineering, water transportation and, in some cases, farming requirements; in Central Asia it is irrigation and power engineering; in the Far East, particularly the Amur River basin, water transportation and flood control.
It is obvious that fisheries is an integral part of the integrated utilization of reservoirs in any geographical area.
According to M.A. Fortunatov (1959), at present there are about 3,000 reservoirs in the world, the area of only several score of them exceeding 100,000 ha. In our country the total area of the reservoirs put into operation has exceeded 5 million ha. In the near future it is to increase to 10 to 11 million ha. The Soviet Union has the largest reservoirs in the world, such as Kuybyshevskoye (644,000 ha), Phy Rybinskoye (455,000 ha), Volgogradskoye (347,000 ha), Tzimljanskoye (270,000 ha), Kakhovskoye (215,000 ha) and many others.
The construction of the Bratzkoye reservoir on the Angara River (550,000 ha) and the Krasnoyarskoye reservoir on the Yenisey River (210,000 ha) has been completed. There are plans for the construction of still larger reservoirs on the lower Ob and Lena Rivers and in the Selenga River basin. The complex of the Kamskoye-Recherskoye and Vychegskoye reservoirs which will channel the north river run off into the Volga River basin is being worked out. The Volga and Dnieper will be transformed into a cascade of large reservoirs along their complete courses.
Reservoirs are of considerable potential importance for fisheries and their high quality fish output can be millions of tons.
The reservoir water regime can be controlled by man. It is evident that fish stocks in the reservoirs can be controlled by man to an even greater extent than in the rivers and lakes which form them.
Each hectare of reservoir area can yield an average of 20 to 30 kg more of high quality fish products, provided fishery measures are adequate and effective. Even now, the fish catch is 44,000 t per year, though only some of the reservoirs have been used commercially.
In the near future the fish output of the U.S.S.R. reservoirs may rise to 170,000 t. When the Volga cascade of reservoirs is completed, its annual fish output may exceed 70,000 t and the Dnieper cascade 35,000 t.
Big actual catches in some of the reservoirs of this type are convincing proof of the feasibility of the target figures. The output of the Tzimljanskoye reservoir has reached 48 kg/ha, while in the Vesselovskoye reservoir it ranged from 90 to 164 kg/ha (initial stages of service) and in the Kakhovskoye reservoir it amounted to 30 kg/ha (fishing limited).
With reservoirs being constructed so rapidly in our country, fishery management development and all-round studying of these new and peculiar water bodies have become one of the main and practically important scientific problems.
Many scientific, economic and design organizations are engaged in solving this problem, including institutes and branches of the Academies of Sciences of the U.S.S.R. and the Union Republics, GosNIORKH and its branches, VNIIPRKh, The Ukranian Institute of Fishery, Biological Departments of many Universities and Pedagogical Institutes, the Observatory of Hydro-Meteorolo logical Survey, design Institutes and other organizations. All-round investigations carried out on the reservoirs of the Volga, Don, Dnieper, Dnestr, Irtysh, Ob and other rivers furnished valuable scientific data on the formation of physical and chemical conditions, development of plankton, benthos and ichthyofauna which formed the basis for working out the principles of fishery management in these water reservoirs.
Patterns of Ichthyofauna Formation in Reservoirs
It has become possible to bring to light a number of patterns in the processes of ichthyofauna formation and development of fish feed reserves through the analysis of the numerous factual data from the integrated investigations which had been performed on different reservoirs of the U.S.S.R. for many years.
The most essential patterns typical of all plain reservoirs are:
1. Substantial changes in the regime and the whole morpho-ecological nature of rivers, due to their conversion from running water bodies into slow discharge ones, transform radically the long-term established ties and inter-relations between organisms. For example, fluviatile biocenoses are replaced by new ones, some species shift to new spawning and migration ranges, anadromous fish tend to settle down, local stocks of fish form, intraspecific biological differentiation of fish occurs and propagation biotopes and egg-laying substrates change.
The transformation of invertebrate fauna and changes in the specific and quantitative composition of fish and their biology, distribution and adaptability take place within a very short period.
2. A rapid change in feed reserves takes place during the formation of the biohydrochemical conditions of the plain reservoirs. Three sequent trophic phases have been established.
Phase one is a sudden increase in standing crop during the first two years of the reservoir filling, due to the intensive fertilizing of the water and bed soils with submerged vegetation decay products. This results in an intensive development of bacterial flora, plankton and benthos, mainly Tendipedidae, which produce a considerable standing crop as a result of the increase in bloodworm abundance. Substantial feed reserves form and they supply thinned populations of fish with plenty of food. Intensive growth of ichthyomass takes place.
Phase two is a trophic depression phase commencing in the second or third year of reservoir filling and brought about by slowing of the submerged vegetation decomposition. During the trophic depression period the growth of plankton, especially benthos, is inhibited, feed reserves fall short and as fish stocks are abundant, the growth of ichthyomass is inhibited too.
The trophic depression phase lasts from 6 to 10 years in southern reservoirs, up to latitude 55° north, and up to 25 to 30 years in the reservoirs of the northern zone.
Phase three is characterized by new increase in feed reserves and begins in different reservoirs at different times, depending upon the rate of the phytoplankton growth and the amount of organic substances accumulated in the bottom soil. During this phase feed reserves remain at a higher level.
3. The fishery management type of the reservoir develops within the first year of filling and is determined by the initial specific and quantitative composition of the ichthyofauna of the mergingwater bodies.
In case trash fish (roach Rutilus rutilus, perch Perca fluviatilis, Blicca bjoerkna and ruff Acerina cerna) prevail in the ichthyofauna of the merging water bodies, they form dense populations, this resulting in low fish productivity of the reservoir.
And just the opposite, when such food fish as bream (Abramis brama), carp (Cyprinus carpio), zander (Stizostedion lucioperca) and others prevail in the ichthyofauna of the merging water bodies, they ensure a rapid growth of ichthyomass and consequently a higher fish productivity within a short period of time.
4. It is chiefly phytophilous fish that form the ichthyofauna of the reservoirs.
Litho-reophilous fish development in the reservoirs is inhibited due to lower flow speeds, silting and the stone and pebble bed soils no longer serving as spawning biotopes. Within a rather long period their numbers remain limited and in the reservoirs without tributaries they disappear completely.
5. The first year of filling is characterized by the very high rate of reproduction of phytophilous fish, as a result of the flooding of vast new areas of flood plain covered with lavish vegetation, the intense growth of plankton and benthos and the scarcity of fish population. The survival rate of the generation of the first year of filling exceeds 10-fold and sometimes 100-fold that of the fry of the merging ponds and rivers. The generation of the first year forms a robust basis for fishing for many years to come.
It is mainly the water level factor that determines propagation of fish after the first year of filling. Sudden fluctuations in the water level inhibit the growth of water and shoreline vegetation, thus creating unfavorable conditions for fish propogation. The numbers of subsequent generations is many times less than that of the first year.
There are ways of special purpose development of fish stocks and raising fish productivity of reservoirs. Establishment of the major patterns governing the biological condition formation and flora and fauna development in the reservoirs has made it possible to promote control of some of these processes, with a view to changing the fish stock's natural development to benefit the fishery.
It was necessary to work out a complex of fishery management measures, which are being taken on the biggest reservoirs, the specific nature of each being taken into account, to ensure the best utilization of fish stocks and a higher fish productivity of the reservoirs. These measures are:
Stocking the reservoirs with valuable food fish spawners translocated from other water bodies.
The main purpose of this is the strengthening of spawning stocks during the first year of filling to ensure an overwhelming abundance of fry, which would prevail in all feeding areas, thus inhibiting the growth of trash fish.
Construction of fish spawning and rearing farms - at the reservoirs for breeding valuable fish fry and their release into the reservoir.
Acclimatization of new species and food organisms. The main purpose is qualitative improvement in the composition of fish stocks and enrichment of the food reserves of the reservoirs with crustaceans to do away with unfavorable conditions of fish feeding within the period of trophic depression.
Construction of fishways, fish elevators and fish screens at the dams of hydroelectric stations.
This is primarily to preserve and replenish the stocks of anadromous and semianadromous fish (Acipenseridae, Salmonidae, Clupeidae, Anguilla anguilla, Vimba vimba, persa, etc.).
Protection and planning of fishing at the first stage of fish stock formation by:
A complete ban on fishing for valuable food species for two years prior to filling and during the first years after the formation of the reservoirs to save spawner stocks for use under the favorable propagation conditions within the first year and to obtain huge populations of fry.
Inhibition of trash fish by special methods of catching and biological means (predators) for a reduction in trash fish abundance to weaken their food competition with valuable food fish.
Among other measures aiding in the rational utilization of fish stocks are: preparation of the bottom of reservoirs for commercial fishing; ascertaining the optimal water level regime; development of artificial spawning areas, etc.
We shall consider the Tzimljanskoye reservoir as an example to show the importance of the human factor in the formation process of fish stocks, raising of fish productivity and a more efficient utilization of fish stocks in new water bodies.
Experience gained in the special purpose development of fish stocks and raising the fish productivity of the Tzimljanskoye reservoir is described here.
The Tzimljanskoye reservoir was formed in 1952. Stretching from north-east to southwest for more than 240 km, it covers the vast fertile valley of the middle and, partially, lower course of the Don River. The area of the reservoir is 270,000 ha, its width ranges from 3 to 42 km, the average depth is 9 m, and maximum depth 35 m.
A highly productive fishery, with bream, wild carp and zander as predominant species, was to be developed in the reservoir on the basis of its natural conditions and planned implementation of some fishery management measures. The total catch in 1957 was estimated as 11,000 t or 40 kg/ha.
The development of the fishery in the Tzimljanskoye reservoir may be divided into two stages.
The first stage was the accumulation of valuable food fish and intensive catching of trash fish.
The second stage was the commercial utilization of food fish stocks on the basis of planned fishing.
The main measures aimed at the required development of ichthyofauna were taken during the first period which lasted for five years (1952–56).
Food fish in the initial ichthyofauna being insufficient, large quantities of bream, carp and zander spawners were transplanted from the Don delta. A year prior to filling, the reservoir was stocked with 136,900 bream, 28,600 carp and 6,900 zander.
The strengthening of the spawning stocks of these fish, timed to the first year of filling when the propagation and nutrition conditions would become most favorable, contributed considerably to the increase in fish progeny. The 1952 generation of bream and wild carp was so abundant that it is prevailed in the catches of all subsequent years, making up 68 to 97 percent of the bream stock and 95 to 98 percent of the wild carp stock (age structure). Only part of the first and exceptionally abundant generation of semianadromous zander was preserved in the reservoir due to the downstream migration and perishing of the fingerlings caused by the food shortage.
Local fish (Abramis ballerus, pike and Blicca bjoerkna), extremely abundant by the time the reservoir had been filled, produced a mass outbreak as well.
The first year generation formed the main commercial fishing stock which was then used for 6 to 10 years. The total fish output due to the first year generation was over 10,000 t of bream, 3,000 t of wild carp, 5,300 t of Abramis ballerus and 7,300 t of pike.
The strengthening of the spawning stocks of food fish, timed to the moment the reservoir had been filled, was effective on the Kakhovskoye reservoir, where 85,500 bream, 45,500 carp and 4,500 zander had been stocked.
Similarly good results were obtained on the Vesselovskoye and Kuybyshevskoye reservoirs. The Volgogradskoye, Kuybyshevskoye and Kakhovskoye reservoirs were stocked, not only with spawners, but with a great amount of food fish fry and fertilized eggs to increase their number.
Large scale fishing for trash fish and pike was timed to the first period of the Tzimljanskoye reservoir development. Planned fishing was carried out during four years. During this period fishing for food fish was completely prohibited.
During 1953–56 the catch of fish was 3,580 t, mostly Blicca bjoerkna, Roach (Abramis sapa), perch, ruff, etc.; 4,630 t of pike and 4,890 t of Abramis ballerus. The total of 13,100 t of trash fish was removed from the reservoir and the 15 million specimens of bream, wild carp and zander caught were released back into the reservoir.
Such selective fishing brought about the scarcity of unprotected fish stocks and a considerable fish output even during the first years of the reservoir existence on the one hand and better feeding conditions and increased abundance for valuable game fish on the other.
The catching of trash fish as a method of special purpose influence on the formation of ichthyofauna proved effective on other reservoirs as well. During the first three years (1956–58) the catch of trash fish on the Kakhovskoye reservoir was 10,600 t; on the Kuybyshevskoye reservoir during the first three years (1957–59) 5,600 t, and on the Volgogradskoye reservoir during the five years (1959–63), 7,380 t.
The planting of Mysidacea and some Polychaeta timed to the beginning of the trophic depression stage, contributed much to raising the fish productivity of the Tzimljanskoye reservoir.
Between 1954 and 1957 8 million specimens of Mysidacea and 3 million Polychaeta were transplanted from the delta of the Don River. They adapted themselves to the new conditions soon and served as food for bream, Lucioperca volgensis, Pelecus cultratus, zander fry and other fish. The deficiency of food involved in the trophic depression period was made up to a certain degree by the newly-acclimated organisms and the lowering of the fish growth rate, i.e., the rate of the ichthyomass growth being arrested. Due to this measure the high fish productivity of the reservoir has been preserved until the present time.
The acclimatization of food organisms carried out on the Dneprovskoye Vesselovskoye and Kakhovskoye reservoirs has shown good results as well. At present the Kuybyshevskoye and Volgogradskoye reservoirs are being planted with Mysidacae and Polychaeta. The stocking material comes from the Tzimljanskoye reservoir.
To ensure a rational utilization of fish stocks and maximum fish output, it is necessary to remove all timber and underbrush from the reservoir bottom and to prepare dragging areas required for fishing. The bed of the Tzimljanskoye reservoir had been cleared before filling and, eight dragging areas had been prepared in different parts, (for application of trawlnets and seines) to a total of 130,000 ha, i.e., 49 percent of the whole reservoir area. These measures permitted fishing in nearly all parts of the reservoir and utilization of different active and passive fishing facilities (trawls, seines, driftnets, fixed seines, hoopnets and other traps).
The water level regime is one of the main factors determining fish productivity of all the reservoirs of our country, including Tzimljanskoye. Due to fluctuations of the water level determined by the yearly water supply, abundant generations of fish are not frequent in the reservoirs. For instance, in the Tzimljanskoye reservoir within the past 12 years only two abundant generations (1952 and 1963) and one generation of average abundance were observed. All the other years were characterized by scanty generations which could not compensate sufficiently for the stocks, diminishing as a result of fishing and other factors. Fluctuations in water level adversely affect the reproduction especially of such fish as wild carp, Abramis ballerus and pike, which are particularly sensitive to substrate and propagation condition changes.
The unfavorable effect of water shortages upon fish propagation may be counteracted to a certain extent by means of water level regulation measures taken in springtime during spawning periods.
Therefore, special water level regulation schedules are drawn up for the large reservoirs of our country. These schedules take into account fishery management requirements and are subject to approval by governmental authorities.
The second stage of fishery management development on the Tzimljanskoye reservoir started in 1957 when the first reservoir generation of the main mass of all the food fish had attained sexual maturity. By that time the formation of ichthyofauna had been completed and the period of full scale commercial fishing for all species began.
Fishing on the Tzimljanskoye reservoir has been done since 1957 on the basis of a planned limitation of valuable fish catches. The catch limits are set for each year and separately for each species, depending upon the condition of the stocks of the particular species. At the same time, obligatory figures have been set for the minimum trash fish catch.
Limitation of food fish catches is one of the most important factors in fishing control on the Tzimljanskoye type reservoirs where food fish stocks are not stable due to the irregularity of their replenishment. The aim of fishing control is to ensure that the catch of food fish does not exceed a fixed limit, i.e., a maximum value, substantiated biologically.
On the contrary, the catch of trash fish is not limited and the minimum catch figure set may be exceeded considerably.
It is necessary to know the number of a given species stock and to determine the permissible percentage of this stock utilization to substantiate the catch limit.
The determination of the size of food fish stocks in the Tzimljanskoye reservoir is made by means of the direct quantitative registration method, i.e., on the basis of average yearly figures of fish populations (fish catch per area unit and fishing gear unit).
According to the experience gained in utilization of reservoir fish stocks, fish with a shorter period of sexual maturity and that are adaptable to a comparatively wide propagation range (zander, Lucioperca volgensis, Pelecus cultratus, Abramis ballerus) are able to make up for 40 to 45 percent losses in fishing stocks.
Fish with a longer period of sexual maturity (bream) can compensate for 30 to 35 percent losses only.
The fish productivity of the Tzimljanskoye reservoir was raised to 45 kg/ha, as a result of the special-purpose fish stock development measures and the introduction of catch limitations on food fish. Annual catches on this reservoir rose rapidly:
1953 (the second year of filling) - 900 t
1957 (the sixth year of filling) - 6,670 t
1962 (the tenth year of filling) - 11,000 t, i.e., the target figure of fish output was attained. The catch of valuable food fish (bream, wild carp, zander, Abramis ballerus, pike, Silurus glanis, Lucioperca volgensis) was 6,850 t or 62.3 percent of the total catch.
Im some years the catches were as high as:
Bream - 4,750 t (43.2 percent of the total catch)
Wild carp - 9,000 t (9.7 percent of the total catch)
Zander - 1,000 t (9.0 percent of the total catch)
Abramis ballerus - 1,950 t (40.5 percent of the total catch)
Pike - 1,840 t (40.7 percent of the total catch)
Sheat fish - 1,000 t (9.0 percent of the total catch)
Lucioperca volgensis - 1,400 t (13.0 percent of the total catch)
The total fish catch within the 12 years of the fishery management operation on the Tzimljanskoye reservoir was 87,800 t.
The expenditures for fishery management, preparation of the reservoir and the measures aimed at special-purpose development of fish stocks and raising of fish productivity have been justified completely and earned a sizable profit.
The fish catch level attained in the Tzimljanskoye reservoir is not the limit. More numerous food fish stocks can be reared due to the successful acclimatization of Mysidaceae and Polychaeta and the intensive development of phytoplankton, zooplankton and zoobenthos.
Since 1963 we have been concerned with planting of Hypophthalmichthys molitrix, as a consumer of phytoplankton, with a view to a more rational utilization of the existing food reserves and further raising of natural fish productivity of the reservoir. At this time the work connected with the stocking of the reservoir with the fry of Hypophthalmichthys molitrix may be stepped up considerably, owing to the creation of the stock of this species at the Tzimljanskoye fish spawning and rearing farm. The acclimatization of Hypophthalmichthys molitrix will permit utilization of the unlimited food reserves (phytoplankton) and raise the reservoir fish productivity considerably.
Lately, wild carp fry reared on the spawning and rearing farm have been released to strengthen the wild carp stocks and to better utilize the supply of food molluscs. The wild carp fry is released because the natural reproduction of this species fails to ensure the required abundance.
Much work is to be put into rehabilitation of the natural spawning areas and development of spawning areas with a regulated water level regime, independent of natural high floods, to secure a stable fish output increase annually. The research work required for selecting such areas was carried out in 1963–64. On the Tzimljanskoye reservoir the catches will grow to 15,000 t (or 55 to 60 kg/ha) annually due to the stocking with Hypophthalmichthys molitrix and wild carp fry and the rehabilitation of the spawning areas.
The Tzimljanskoye reservoir is not the only one where fish productivity has been raised.
Fish stocks and catches are growing on the Kakhovskoye, Kuybyshevskoye, Volgogradskoye and other large reservoirs where the initial stage of the fish stock formation is not complete yet. The fish catches on the Kakhovskoye reservoir had approached the target figure (10,000 t) and totalled approximately 7,500 t in 1964.
On the Kuybyshevskoye reservoir the catches rose from 800 to 4,650 t; on the Volgogradskoye reservoir from 600 to 2,900 t. On the Kremenchugskoye reservoir, completed in 1960, the catches rose from 740 to 4,050 t.
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