, ARCHIVES
FISHERIES RESEARCH BOARD OF CANADA
Transla^ion Series No. 363
RESULTS OF THREE YEARS OF OBSERVATIONS ON FISH BELOW
THE LENIN,.HYDROELECTRIC STATION ON THE VOLQA
By A.. T. Diûzhikov (Saratov Branch at the State Institute-for Lake and River Fisheries--GosNIORKh)
Original title: Rezultaty t^ekhletnikh nabliûdeni^ za rybami v nizhnem befe volzhskoi GES im. V. I. Lenina.
From: Voprosy Ikhtiologii, Vol. 1, No. 1(18), pp. 69-78,: 1961. Moscow.
Preliminary translation by W. E. Ricker
Distributed by the,.AFisherdes, Res:éaroh:,Board of Canada Biological Station, Nanaimo, B. C.
1961 .e*
This is a preliminary translation prepared for the use of the Fisheries Research Board of Canada. It is not a definitive English version of the article, and it has not been checked or approved by the author. The Volga River below the ci^y of Kuibyshev was closed off by.the Volga Hydroelectric Station in the autumn of 1955. The Kui.byshev reservoir was filled in three stages: autumn 1955, spring 1956, and spring 1957. The right bank below the hydro- electric station is steep: the Zhigulev Mountains.come ri,ght down to the water. On the left side, for 12 km the river is held back by the dam of the navigation canal, which prevents the exit of the water from the main channel into the system of side channels. On the side of the river adjacent to the hydro- electric station there is an accelerated current speed especially at high water. In addition to its seasonal fluctua- tions, the level of the water below the dam is subject to sharp weekly changes, caused by the working plan of the hydroelectric $tation, In comparison with the former regime of the Volga, below the dam there has been some reduction in the height of high water, and some increase in the mean level, as well as slower warming of the water in spring and cooling off in autumn.
In the channel of the river sandy bottom prevails, but along the right bank there is a zone of gravel bottom, expanding locally into bars where lithorheophilic fishes spawn. In the part of the left bank region lying near the hydroelectric station, on islands and on narrow strips of the inundated parts of the right bank, lithorheophilic iish can reproduce. The directions of the currents below the dam change in relation to the flow of water through the sluiceways of the dam and the turbines (Diûzhikov, 1958).
Species composition and concentration of fishes
Below the dam there are found 6 anadromous species of fish and 25 river speçies. Among the anadromous fishes the following occur in commercial numbers: the Russian sturgeon or osëtr [Acipenser üldenstëdtii], beluga [Huso huso], inconnu [Stenodus leucichthysJ, and in some years the black-backed shad [Alosa kesslerT . The Caspian lamprey [Cas.piomyzon wagneri'] appears there in abundance at the end of winter and early spring, a time when the break-up of the ice and ice movements interfere with its capture. Among the river fishes, those usually occurrin in the commercial catches are the sterlet, ci enser ruthenus^, bream [Abramis brama], white bream. [B1 icça;., .' oel-ian _., blue bream [Abramisaal^lérus , white-eye [Abramis sapa zander [•Stizostedion lucio erca], Volga zander LS. vol ensis], perch [Perca fluviatilus , pike [Fsox lucius], ide Leuciscus idus], asp LAspi.us aspius], catfish LSilurus lanis , chekhon Pelecus cultratus], burbot [Lota lota , roach Rutilus rutilus], and rarely other speciès. Infine-méshed experimental fishing apparatus the gudgeon [Gobio gobio] has been taken in consider- able quantities, and raréT-ythe sculpin [Cottus gobio] and spiny loach [Cobitis taenia].
Before the closing of the river by the Volga gydroelectric Dam the most numerous fish were bream, white-e'ye, blue bream 2
and white bream, which we will link together as th^"bream group, and sterl.ets were numerous, After closing of the xiver. the fish fauna below the dam began to'changé; In 1956:the"relâtive abundance of the species was that typical.of "rive.r "species, -but in the following two years the.,percentage of sterlets and,of the bream-group decreaseda while the.percentage of'pi-ke and percids increased sharpl.y (Table 1).
Considerable accumul.itions developed,, below the dam9 of " adult anadromous hi6mal os"UYr .(Berg.1 1934), They arrived at the dam toward the end of summer and early autumn-;. at the end of September in the clear water [page 70,] a h;i__gh concentration of sturgeon could already be observed,The maximum catches of' one "vozmilkall per night in September 1956 were 15420 sturgeon, in 1957 10y15, and in 1958 10-15. By trawling"with a small trawl from a seiner in September 1958 2-3 sturgeon were c^pu.ght per minute. The catch of a 100-metre series of 60-rmm fixed gill nets set in the quiet zones at the sâmé time was 6-7 sturgeon per night.
The inconnu was encountered near the Volga Hydroelectric Station from early spring to late autumn, but its catches were not very great, in all 3-5 fish per night per floatin"g. gill net.
Lampreys in 1956 and 1957 were caught as occasional_,... specimens in early spring. In May 1958, at the 15ui:.^c^^.r^^.)h,ou^;ing the hydroelectric station, a massive accumulation of lampreÿs was observed; many of them were caught with bag-liké nets made of inetal.
Occasional specimens of beluga were encountered,_but according to the fishermen they were more frequent than formerly. The akhany and "vozmilki", used to catch sterlets below the dam" frequently were torn by the beluga--even those made from kapron 60-mm mesh webbing. Hence the catches do not reflect its true abundance.
Black-backed shad were caught occasionally in June and July, at a distance of 10-20 km below the hydroelectric station... In 1956 400-metre seines caught several tons of shad in the:main channel 25 km below the dam.
Of the river fishes, in 1957 and 1958 accumulations were observed below the dam of pike only, which were.moving down- stream in large numbers from the Kuib.yshev'reservoir. The abundance of pike below the dam began to,grow in the autitmn of 1956 and gradually increased during the two following years. In the 100-metre series of 50-60-mm kapron fixed gill nets 5-10 [per day?] were caught in the spring of 1957, 20-25 in summer, and 35-40 in autumn; in the autumn of-1958 the average catch amounted to 50 individuals, and pike comprised 40% of the numbers and 90% by weight of all fish caught at that time below the dam (Diûzhikov, 1959). Few other river fishes were encountered here. This is to be explained by the absence of a 3
Table 1. [page 70] Species distribution of catches below the Volga Hydroelectric Station (%).
Total Anad- Ster- Bream Per- Year romàus let group cidae Pike Ide Others %. Pieces
1956 9.2 17.1 59.9 2.9 0.1 7.0 3.8 100.0 2816 1957 6.2 13.0 30.1 11.1 30.4 5.2 4.0 100.0 2898 1958 4.8 7.7 31.4 11.1 39.5 2.7 2.8 100.0 1797
Table 2. [page 71] Length distribution of osetr [Acipens-er 21:11denstgdtii] below the Volga Hydro-
- electric Station.
Body length to tip of tail, cm
Year 0-50 50-100 100-150 150-200 nn
1956 9 66 132 5 212 1957 17 72 310 10 409 1958 32 12 183 10 237 r.
Table 3. [page 71] Weight distribution of osëtr below the Volga Hydroelectric Station.
Time Weight, kg of catch 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40
Fall 1956 4 32 11 3 - 1 - 1 52 Fall 1957 • 20 88 84 41 18 10 5 - 266 Fall 1958 2 19 31 11 3 1 - - 67 4
sufficiently large ^pawning stock below the hydroelectric dam and in the reservoir. .6 The composition of the stock of certain species of fishes
The stu^geon below the dam were re.presented by fish of very varied size and weight (Tables 2 and 3). However the sexually mature part of the stock was well separated from the immatures; individuals in stage III of maturity were lacking near the dam.
In 1956 and 1957 the fillin,g.-of the Kuibyshev reservqir was in progress and immature sturgeon in large numbers weré encountL-red near the dam in the sprin.g and summer, f-ewer in autumn. The appearance of young sturgeon in these years near the Volga dam was associated with their downstream movement out of the filling reservoir. Apparently young fish of the older age groups, which are very numerous.in the middle Volga, moved downstream especially intensively (Lukin, 1937, 1947)_ Thbs I— predomlnânce in 1956 and 1957 [page 71] of fi-sh of a length of.. more than 50 cm among the immature sturgeons is to be e.xplairied in this way. In 1958 individuals more than 50 cm were rarely encountered in the sexually immature part of the stock.
The sexually mature part of the stock of s.turgeon near the dam was represented by not -particularly large fish ,(less than 150 cm and less than 20 kg). In almost all samples femalés comprised about 20% of the total number of individuals (Tables-;4 and 5). But at the end of the spawning season a sharp increase in percentage of males was observed, occasiôned by their prolonged stay on the spawning grounds (spring of 1956). In autumn and in spring sexually mature sturgeons were in stage IV of maturity., and in summer in stage VI,
Thus below the hydroelectric station we had to deal with the so-called hiemal form of sturgeon [osëtr], characterized on the Volga by moderate size of the adult spawners, a high percentage of males in the spawning stock, and by spawning in May on the shoreward gravelly layers that are flooded at -+À,.: high water (Aliavdina, 1951). R,art of the earliest-arriving spawners of the hiemal osëtr, assigned by N. L. Gerbilsky (1957) to the summer run [letnii khod] biological group,,go up as far as the Volga Hydroelectric Station..
Fishermen reported the appearance below the dam in July- August of occasional specimens of sevriuga and large osëtr in stage IV of maturity. Apparently spawners belonging to the late vernal form of acipenserid fishes (Gerbilsky, 1957) reach that point only in small numbers, and not every year.
[page 72] Only mature inconnu were observed at the Volga Hydroelectric Station. Their length varied from 70 to 100 cm, their weight from 4 to 9 kg, and their age from 6 to 10 years (Tables 6, 7 and 8). Most frequently encountered were 5
Table 4. [page 71] Len-gth and sex -distribution of mature osëtr below the Volga Hydroelectric Station.,
W Length to tip of tail, cm Time N °' of - ^ ^ n +-' catch 90- 10Q= 110- 120- 130- 140- 150- 160- 170- UE 100 _110!_'. 120 130 140 150 160 170 180
Spring 1956 (end of 6 25 17 8 5 - - 1 62 3.2 spawning)
Fall 1956 - 4 17 12 7 3 2 1 46 26.1
Spring 1957 1 1 .8 6 5 2 1 - 24 20.8
Fall 1957 1. 4 15 13 9 7 - - - 49 24.5
Spring 1958 3 9 40 39 17 12 4 2 - 126 15.0
Fall 1958 1 3 10 23 15 5 3 - - 60 21.7
Tabl-6. 5. [page 72] Weight distribution of mature osëtr`.below the Volga Hydroelectric Station in the autumn of 1957.
Weight, kg
Sex 0-5 )5T101i 10=.L5 15-20 20-25 25-30 30-35 Av. n
Females 1 7 15 8. 4 4 19.9 39
Males . 4 80 74 27 9 6 - 11.9 200 6
Table 6. [page 72] Size and sex distribution of inconnu below the Volga Hydroelectric.Station. 1 Fork length of-body, cm Perçent- age Year 70- 7,5- 80- 85- 90- 95- females n 7.5 80 85 90 95 100 Av.
1956 1 2 3 1 3 2 86.2 41..7 12
1957 - m 3 9 7 -, 88.6 47.-4 19
1958 - M 1 9 12 3 90. 48.0 . ^ , 5
Table 7. [page 72] Weight çlis- Table 8. [..page 72] Age tribution of inconnu below the distribution of inconnu Volga Hydroelectric Station. below the Volga Hydro- electric Station. Weight, kg Age in years Sex 4-5 5-6 6-7 7-8 8-9 n Year 6 7 Males 1 4 4 3 - 12 1956. 1 7 2 l. 1 12 Females - - 1 4 2 L7 1957 1 12 6- - 19 1958 2 9 7- - 18
Table 9. [page 72] Length distribution of black-backed shad below the Volga Hydroelectric Station in 1956.
Fork length of body, cm
Sex 30- 32- 34- 36- 38- 40- 42- 44- 46- n 32 34 36 38 40 42 44 46 48
F em a l e s 2 3 2 20
Males 2 8 19 9 14 8 4 - - 64 - 7, -
Table 10. [p ag e 73] Length distribution of lampreys below the Volga Hydroelectric Station in 1958.
Length to tip of tail, cm
Sex 31- 32- 33- 34- 35- 36- 37- 38- 39- 40- 41- 46- Av. . 32 33 34 35 36 37 38 39 40 41 42 47 n
Males 1 - 4 7 5 15 14 9 2 7 - 1 37.1 65
Females 3 1 3 8 7 5 3 3 - 38.2 33
Table 11. [page 73] Weight distribution of lampreys below the Volga Hydr6^e4._eotric Station in 1958.
Body weight, g
U a) CD Ln '0 ,zt d' L() Lc) ^IO \O [-- P- 00 c0 ^ ^ Sex ^ o €• ^ ^ e a s ^ ^ ^ Av. n à Oà O Ln O ^ O^ O^ (D M -I- d- L() i.C) \1O \1O l^ l- 00 CO d1\ a,
Males 1 - 2 6 15 7 16 7 4 2 2 2 - 1 66.1 65
Females -- 1 2 2 4 10 2 6 3 2 - 1 - 70.4 33
Table 12. [page 73] Length distribution of sterlets below the Volga Hydroelectric Station.
Length to tip of tail, cm
O Ln O Ln O Ln O Ln O Ln o Ln O Lc7 OLn 00 Y e a r CV C'^J Co (Y) d- d' Ln L(-) ^O ,0 t^ [- CO CO d^ d^ r{. n ^ ^ ^ I r ! 1 1 1 e ! ! 1 ^ 1 1 1 à Q ^ O ^ O LC) O ^ O t.C) O i.(^ O tf) O ^ rl N N M M d` - d' LC) LC) ^ ^O [- l- Co CO O\ p,
1956 1 r7.-8 13 15 20 29 23 8 7 4 1 1 1-- 138
1957 23 46 31 45 31 41 35 34 21 15 7 3 1 2 1 1 337
1958 - 17 63 48 23 41 40 38 40 23 11 ------344 8
individuals 80 to 95 cm long, 6 to 8 kg in weight and of age 7 or 8. Females comprised somewhat less than half of all thése fish.
Of the shads, the only one which reached the Volga Hydro- electric Station was the anadromous form having an intermediate number of gill rakers, the blaçk-backed shad (Zamakhaev, 1-944; Diûzhikov, 1955.). The main mass of females were of large size, but among the males medium-sizqd fish were rather common; such fish used to lPe referred to tho so-call^d Volga few-rakered shad (Table 9).
[page 73.] Caspian lampreys at the Volga Hydroelectriç Station were of ordinary size and weight (Tables 10 and 11). However the percentagte of females (33.7) was less than at Saratov (Diûzhikov, 1956).
The sterlets below the dam were of varioussizes and age-s (Tables 12 and 13), mainly 25-65 cm long and fr.Qm 2-3 to 10-12 years old. The rather diverse ago compo_^ition ançl large number of fish of the oldest age categories indicates the relatively favourable condition of the sterlet stocks in this region before the regulation of the river.
By 1958 the number of the oldest and largest sterl^ts at the Volga Hydroelectric Station had noticeably decreased.
The composition and abundance of the sterlet stock near the dam depended on downstream migration of this fish from the Kuibyshev reservoir. Below the dam, in the sector from Kuibyshev to Saratov, the abundance of sterl-ets had considelp- ably declined in recent years because of serious pollution of the river by petroleum. The presence below the dam, during the years the Kuibyshev reservoir was filling, of large numbers of sterlets more than 70 cm long and older than 15 years might be explained by an intensive downstream migration during.these years out of the reservoir. The younger age composition of the stprl:et stock TDslow the dam in 1958 is associated with their intensive (and for the most part illegal) removal by fishing, along with a decline in the downstream migration from above the dam.
[page 74] The pike below the dam in 1957 and 1958 were represented by large fish, 45 to 75 cm in length and 2 to 4 kg in weight. In the fall of 1958 pike were found of an age 2+ to 6+; the most numerous group were individuals of the 1954 year- class (4+). 9
Table 13. [.page 73] Age distribution of sterlets below the Volga Hydroelectric Station, %.
Age in years
Year 0-5 5-10 10-15 15-20 n
1956 21:,0 42.8 27.5 8.7 138
1957 40.3 31.8 19.3 8.6 3^7
1958 32.8 31.7 31.1 4.4 344
Table 14. [page 74] Degree of maturity of the gonads among inconnu below the Volga Hydroelectric Station in 1956-1958.
Sex and February- April- June- September- stage of March May July October n maturity
Males III 2 7 11 20
6
2
Females III - 10 4 - 14
IV - - 2 9 11 - 10 -
Maturation and reproduction of fish below the I Volga Hydroelectric Station
Anadromous aci-penseridsmmthe hiema,l osëtr and beluga--on arriving below the dam in autumn were in stage IV of maturity, By the end of September the ovocytes as.a rule had already completed stage IV,; polarity was well developed., the nucleus was situated at the animal pole close to the sac of the ovoçyte. After these fish had wintered over below the dam their_gonads preserved all characteristics of no_rmally,developed organs.
At the time of warming of the water to 8--^9.0 the osëtr and beluga spawners assembled on the rightrnbank grâvel bars and spawned there during 7-10 days. Normally-develo-ping-eggs and larvae of acipenserids were obtained on the spawning grounds in great numbers. In the post-spawning.period young sturgeon, beluga and sterlets were observed below the spawning grounos. All this indicates successful maturation and reproductiv^ of spring-spawning acipenserids below the Volga Hydroelectric Station,
After the spring spawning, all the osëtr, beluga and sterl6t spawners had.^sexual products in stage VI. In July and August female sterlets were found with traces of resorption of the ovaries; in September 1957 a female osëtr was found below the dam with ovaries in a condition of resorption.
Spring-spawning acipenserid fishes of the Volga, because they don't all mature at the same time, do not all succeed in completing spawning, in years of early high water, before the rapid fall in the water level. It is possible that the spawners delayed beyond this time spawn on gravel bars of the main channel of the river (Aliavdina, 1954). Below the hydro- electric station there are no main channel bars, and any sturgeons that had not successfully spawned by the time of the fall in water level, mainly sterlets, would find themselves, after the fall, in conditions where they would scarcely be able to reproduce normally. Apparently spawners of the vernal form of acipenserid fishes,which arrived in small numbers below.the hydroelectric station, would also find themselves in this position.
Inconnus appear below the hydroelectric station at the end of winter and beginning of spring. In April and Ma inconnu spawners are in the stage III of maturity (Table 14^.
At the end of summer the sexual products of female inconnus are in stage IV. In 1957 females with running eggs were found:at the end of the first 10 days of November when the water temperature was 60; in 1958, according to the observer Z. I. Savina, males with running milt appeared on October 9 at a temperature of 100, and females on October 29 at a temperature - 11 -
of 7.60. In 1956 and 1957 about half a million fertili:^ed egg.s of inconnus iveie obtained below the-dam for fish cultural purposes, [page 75] and in 1958 3.5 million. All this indicates the normal maturation of the sexual products in inconnus when they are held below.the dam.
Female inconnus with running eggs were found in places not suitable for the spawning of these fi.sh; in calm.parts of the shore zone and in backwaters. The absence of fine _grav(pl bars below the dam forced the inconnus to lay their eggs under whatever conditions they could find. The fact that the inconnus did spawn near the dam is indicated not only by the discovery of males with running milt, but also by their rapid disappearance from the downstream area immediately after spawning temperatures were reached. Neither.at the dam nor at Saratov did we find inconnu females with degenerating ^ggs during the.post-spawning period. Efforts to obtain eggs deposited by inconnu below the dam were also fruitless. However from the reservoir relatively warm water from the deep layers flowed downstream through the turbines; therefore incubation of the inconnu eggs below the dam took place at temperatures higher than usual.
The black-backed shad appeared below the dam at the end of June'and beginning of July in condition to deposit the last portion of their eggs; no post-spawning mortality was observed below the dam. In August the shad there began actively feeding. Apparently reproduction of the black-backed shad below the dam took,place more or less successfully.
In 1958 Caspian lampreys below the Volga hydroeleçtric dam were in stage IV of maturity up to the end of May. This contradicts the theory of early spring spawning of lampreys in the Volga _(Pravdin, 1913). We were not successful in following them right through to the time of their reproduction below the dam.
As for the phytophilic ecological group of fishes, among them too no cases of resorption of the sexual products were observed.
Thus the.water regime below the Volga Hydroelectric Station is favourable for the maturation of the sexual products of the mature spawners of the majority of Volga fishes. Spring-spawning lithorheophilic and phytophilic fishes reproduce here successfully. Because of the absence of gravel in the channel below the dam we cannot expect successful reproduction of the vernal form of acipenserids and inconnu. For the spawning of inconnu and other salmonid fishes, which réproduçe in autumn in shallow parts of the river having ^a coarse gravel bottom, the region below the dam is not favourable because of the sharp fluctuations in water level during the period in question. Under such conditions mass mortality of eggs is likely, from dessication and freezing. - 12 u
On the behaviour and mortality of fish below the
Volga Hydroelectric Station
Mature os9tr spawners remain in the 10-km stretch of river adjacent to the hydroelectric station from autumn to spring. In spring, with the b.e_ginning of the discharge of the flood waters, os9tr become scarce in the immediate neighbourhood of the hydroelectric station;. at the same time a spawni.ng concentration of os9tr ap ears at a somewhat greater distance from downstream (10-20 km^a The higher the flood waters and the greater the speed of the current, the farther below the dam spawning takes placeo Observations on the behaviour of the acipenserids below the turbines and spillways show:, that when the current is not too great (less than 3 m per second) osëtr come right up to the mouths of the turbines and approach very close to the spl.llways o However osëtr can remain in su*ch channels for only a certain time9 and then leave for quieter parts of the river. Ordinarily such are.as are to be.found close to the dam, but at times of high water they are 10-20 km distant. Apparently downstream movement is delayed and the osëtr accumulate on bars in the zone of transition from the increased current speeds to those whiGh are usual for the Volga (maximum not more than 2 m per second).
Downstream migration of adult sturgeon and yourig aft(Pr spawning is associated with the height of the flooding. Tn 1956 and 1958 the flood level was low and the current speed during the post-sp.awrl.ng period was not very great; downstream movement of spawned-out os9tr [page 76] from the region below the dam lasted up till autumn, and fingerling sturgeon were found there all summer. In 1957 the flood level was high and current was swift, therefore a massive drift of eggs of sturgeon downstream from the spawning grounds was observed; larvae also were quickly carried by the current, and fingerling sturgeon were not found below the dam in summer. The adults after spawning also went downstream quickly in 1957, and up to the middle of summer migrating fish were rare in the sector from Kuibyshev to Saratovo Resistance of os9tr to current begins to weaken as early as the pre-spawning period., when the gonads change from stage IV to stage V (Aslanova, 1952),
The inconnu remain in the swift current from spring to autumn; like the osëtr, they may go right up to the outlet of the turbinesa The lower limit of the zone inhabited by inconnu is apparently much farther away from the dam than the limit for osëtr. In summer and autumn inconnu were observed near Kuibyshev, and they were observed to enter the Sok River which enters the Volga 40 km belovV- the hydroelectric statî.ona It is possible ', that the appearance of inconnu at a considerable distance below the station is a result of their moving downstream when weakened after vain attempts to surmount the high velocities of the current below the turbines, - 13 -
River fishes are encountered in considerable numbers.in the locks of the navigation canal, which shows their ability to make their way from the downstream to the upstream side of the dam and back again.- The greatest accumulation of these fish, especially of pike, was observed in the_flooded zones near the earth dam and at the spillway dam [vodoslivna^.â plotina]. As a result of the mass movement downstream from the reservoir, and possibly also movement upstream from below., from time to time there were many small fish below the dam: bleak [Culter alburnus], perch, roach and the young of other fishçs. This has established favourable conditions for foraging by predacious fishes below,the.dam,
The distribution of fish below the dam undergoes changes with the character of the current. In autumn, on qpening part of the spillway dam, when the current starts in thé dischaFge canal the osëtr enter this cana].; but when the flow of water ceases the sturgeon leave this place and take up their position in a deep hole right beside the spillway dam itself. The sturgeons winter in this hole and in deep portions of the main channel below the power plant.
In 1956.. and 1957 =àAil,arge number of dead and weakened fish could be seen from time to time below the dam. The principal cause of the mortality of these fish was damping [glushenie] by electric current and from the use of explosive substances on objects during construction of the dam. In 1958, with the consolidation [sver#vanie] of the structure, dead and weakened fish began to be less frequent.
Some injury of fish takes place during downstream migra- tion through the turbines and the spillways. However the main mass of the fish which move downstream from above qo not receive any serious injury.
In the flooded portions downstream accumulations of small fishes can be encountered from time to time which have wounds covered with Saprolegnia. The principal cause of the presence of such fish there is that they have been injured by the numerous predators. For example, when large pike attack schools of small fish a considerable part of th^^na'Ï suffer injuries [podranki]. I have found parts of pike teeth in young sturgeon caught in the flooded zone.
Prospects for utilization of the water below the Volga
hydroelectric dam.for fish reproduction
Conditions below theR,Wo^ga Hydroelectric Dam are favourable for the maturation of the se'xûal products of adult Volga fishes of several ecological groups. This opens up wide possibilities for establishing fish-cultural facilities for such fish as 1 , a - 14 -
cannot reproduce[Syccessfully in this region (wholly or in part). It would be useful, for example, to organize artificial culture of sterlets below the dam. Especially desirable would be large- scale rearing of this •ish in years when [page-77].flood-w'at.ers,- subside early, since in these years most of the sterlets probably resorb their sexual products. Preservation of the spawning,grounds of spring-spawning lithorheophilic fishes would permit them to spawn annually below the Volga dam. The various sturgeons are of a special interest. In addition to sterlets, hiemal osgtr and beluga..) ,I;hà-t,i ,hame -beeri passed up over dams farther downstream can reproduce below this dam. In the stretch between the dam and the mouth .of the Sok River the area of the river at flood time can be estimated . provisionally as 10 hectares. Estimating the denaity of osgtr, eggs when laid as 1000 per square metre (Derzhavin,- 1947), and given an average individual fecundity of 200,000 eggs, 500 female osgtr could spawn at one time on this area. . Conditions below the hydroelectric station are also favourable for building artificial gravel bars in the main . channel of the river, since on the right bank here an outcrop , of stony rock comes close to the water. The region below the dam will be particularly important for the reproduction of sturgeons if it is possible to establish a local stock of osgtr in the Saratov reservoir. Thus the region below the Volga Hydroelectric Dam, which in a little while will be converted irito the upper part of the Saratov reservoir, will play a large role in the production of valuable rheophilic fishes, including acipenserids.
Conclusions
1. The water regime below the Volga dam is favourable for maturation of the sexual products of many Volga fishes. Spring- spawning lithorheophilous and phytophilous fishes, and also the pelagic black-backed shad which spawns in summer, will find more or less favourable conditions for reproduction below the dam. Absence of main-channel gravel bars [griâdy] and gravel banks [perekaty], and sharp fluctuations in water level àf the critical period [v mehhennyi period],make the river downstream from the dam unfavourable for reproduction of summer and autumn- spawning lithorheophilic fishes. 2. In the Saratov reservoir, the region below the Volga hydroelectric dam will constitute a place where conditions for the reproduction of many rheophilic fishes will be preserved. By carrying out a series of fîsh-cultural and improvement- • measures it will be possible to develop this region into a place of intensive reproduction of stocks of acipenserid fishes for the Saratov reservoir. - 15 m
3. The composition and abundance of the stocks of fish below the dam depends on the downstream migration of fishes from the reservoir above, and the arrival of fish from the portions of the river lying below. In 1956-1958 a rather large accumulation was observed here of anadromous hiemal osëtr, and of pike which had moved down from the Kuivbyshev reservoir.
4. The osëtr spawners which reached the dam remained close to it. In the spring, when maturation of their gonads gives the spawners less capacity to withstand the current, and when the current speed increases as the flood waters rise, osëtr spawners leave the dam and concentrate on the spawning grounds 10-25 km below its discharge. The higher the flood, the farther from the dam the osëtr spawn.
5. Inconnu spawners have a larger zone of possible spawning places below the dam than do the osëtr. Their spawning was observed }n portions which were favourable for development of the eggs.
6. Both small and medium-sized fish (wéighing up to several kilograms) move downstream rather sudcessfully,through the turbines and spillways of the Volga dam. The number of fish injured during this downstream movement is relatively small. Extremely large fish have received injury as a result of shock..by electric current and use of explosive substances during the construction of the hydroelectric station.
Literature
Aliâvdina, L. A. 1951.. [Condition and distribution of spawning Russian sturgeon and sevriuga in the portion of the Volga River between Saratov and Kamyshin.'] Tr. Saratovsk. otd. Kaspiisk. fil. Vses. n.-i. in-ta morsk. rybn. kh-va i okeânogr., Vol. 1.
1954. [Conditions for reproduction of anadromous and acipenserid fishes below Stalingrad.] Jr. Saratovsk. otd. Kasp. fil. Vses. n.-i, in-ta morsk, rybn. kh-va i okeanogr. (VNIRO) 9"'176].. ?.3';-
Aslanova, N. E. 1952. [Experimental study of fishes in currents.] Dokl. Vses. n,-i, in-ta morsk. rybn. kh-va i okeanogr. (VNIRO), No. 1.
Berg, L. S. 1934. '[Vernal and hiemal races among fishes.] . Izv. AN SSSR, otd, matem. i estestv. nauk, No. 5.
Gerbilsky, N. L. 1957. [Paths of development of intraspecific biological differentiation, types of anadromous-migrants, and the question of the migratory impulse in acipenserid fishes.] Uch, zap. LGU, No. 44. - 16 a
Derzhavin, A. N. 1947. [Production-of stocks of acipenserid fishes.] Baku.
D ûzhikov, A. T. 1955. [Long-term changes in the size composi- tion of spawning stocks of Vol a shads having an intermedi- ate number of gill rakers.] N^uchn, ezhegodn, biôlogo-pochv, fak-ta Saratovsk. un-ta za 1954.
1956. [On the biology of and fishery for Volga lampreys.] Uch, zap. Sâretovsk, un-ta, Vol, 51, No. biol.
1958, [The accumulations of anâdromous fishes below the Kuibyshev reservoir.] Nauchnomtekhn, b^7pl. Vses. n,-i. in-ta ozern, i rechn. rybn, kh-va (VNIbAKh), Nod 6-7.
1959. [Accumulations of pike below the Volga reser- voir.] Rybn. khmvo,. No, 3.
Zamakhaev, D. F, 1944, [The question of the syqtematic position of the anadromous shads of the Caspian Sea.] Zool, zh., Vol. 22, No. 2-3.
Lukin, A. V. 1937. [A biological analysis of sturgeon catches on the Middle Volga.] Izv, AN SSSR, No. l.
1947. [Main features of the ecology of acipenserid fishes of the Middle Volga.] Tr. o-va estestvoisp. pri Kazansk, un-te, Vol. 57, No, 3-4.
Pravdin, I. F, 1913. [Observations on the Caspian lamprey in the spring of 1912.'] Tr, Ikhtiol. labor. Upr. kaqpiisko- volzhsk.: rybn. i tiûlenikh promysl., Vol. 2, No. Ç.
r