Laboratory of Fishery Research and Hydrobiology
The world's biggest salmonid fish, the huchen (Hucho hucho (Linnaeus, 1758)) is now threatened with extinction and has been introduced outside its original area of distribution into several European countries as well as into North Africa and North America. The objectives of the experimental introductions were: (i) to replace disappearing Atlantic salmon (Salmo salar Linnaeus, 1758) or sea trout (Salmo trutta, Linnaeus, 1758); (ii) to introduce a new and interesting game fish; (iii) to control coarse fish populations, and (iv) to save this valuable species from extinction. After reviewing individual experiments, the author concludes that they have mostly failed through ignorance of the ecology of the species, stocking at too young a developmental stage, the short duration of the experiments and the changes in the initial ideas which led to the introduction of this species. The impact of huchen upon the native fish is discussed along with principles for successful introduction and the meaning of the huchen introductions.
Le plus gros salmonidé du monde - le saumon du Danube (Hucho hucho, Linnaeus, 1758) maintenant menacé d'extinction - a été transplanté hors de son aire originale de répartition (le bassin du Danube) et introduit dans plusieurs pays européens ainsi qu'en Afrique du Nord et en Amérique du Nord. Les objectifs des expériences d'introduction et d'acclimatation étaient les suivants: (i) remplacer le saumon atlantique en voie de disparition (Salmo salar, Linnaeus, 1758 -Angleterre, Suisse, Pologne, Tchécoslovaquie); (ii) introduire un nouveau poisson intéressant pour les pêcheurs sportifs (Pologne, Maroc, Belgique, France et Espagne); (iii) limiter les populations de poisson commun (Tchécoslovaquie, Suède); (iv) sauver de l'extinction une espèce précieuse (Tchécoslovaquie, Pologne).
Après avoir passé en revue diverses expériences, l'auteur impute l'échec de la plupart d'entre elles aux facteurs suivants: ignorance de l'écologie de l'espèce, utilisation d'individus trop jeunes, durée insuffisante des expériences, dégradation de l'environnement, manque de suite dans les idées. Dans ses recommandation, il indique les principales règles à suivre pour introduire et acclimater le saumon du Danube.
The biggest salmonid fish still living is the common huchen (Hucho hucho (Linnaeus, 1758)), which is distributed over a very large but disjunctive area. In Europe the species is represented by the nominate form - the Danubian huchen (Hucho hucho hucho (Linnaeus, 1758)) which is confined originally to the basin of the River Danube. An eastern sub-species, the taimen (Hucho hucho taimen (Pallas, 1773)) occurs in the upper part of the Volga River Basin and in the Pechora River Basin in Europe, over the extensive area of Siberia, beginning from the Ob River Basin in the west up to the Yana River in the east and north, in the basin of the Amur River and also in some rivers entering the Okhotsk Sea, respectively. Since ancient time the huchen was appreciated as a valuable food fish. The taimen still has commercial value in some areas while the Danubian huchen is highly appreciated as a game fish. In spite of its great areas of distribution the huchen is now considered to be an endangered species because of the effects on stocks of increasing stream regulation and pollution (Danubian huchen) as well as due to incorrect management taimen). The total world catch of this species is estimated to be about 211–214 t, of which 11–14 t are shared by the nominate form and about 200 t by the taimen. The attempts to establish this species in the new water bodies have been based exclusively on the nominate form (called “huchen” in this paper). Attempts started toward the end of the last century and were closely connected with the first attempts to breed this fish in captivity.
This paper presents a short summary of transplantations and introductions carried out in various countries based on data from Holčík et al. (in press). For the sake of briefness, only a few references are quoted below.
Apart from those rivers to which huchen was native, the species has been transplanted into several rivers of the Danube River Basin previously not inhabited by it and introduced into rivers flowing into the North Sea (Elbe River Basin) and Baltic Sea (the basins of the Vistula and Oder Rivers) respectively. Nine rivers of the Danube River Basin were stocked with huchen and in one river it was reacclimated. This species established itself in all but four smaller streams but at present it is to be found in four streams only, and has disappeared from all others due to pollution and stream regulation. In the Oder River Basin the huchen was stocked into four streams. In two streams naturalization occurred but subsequently the fish disappeared from these too due to pollution. In two further streams huchen stocks are maintained only by repeated stockings. The Poprad River (Vistula River Basin) was stocked with huchen at the end of the nineteenth and at the beginning of the twentieth century. Full naturalization occurred and now this species forms a permanent part of the fish community. The huchen was introduced into six streams of the Elbe River Basin. However, it presently inhabits only a short stretch of the Vltava River upstream of Prague. However natural breeding has not been observed here. The species was introduced into basins of the Rivers Danube, Vistula and Oder in Czechoslovakia both to enlarge the number of streams inhabited by it and to conserve stocks in the face of threatened decline. It was also thought that huchen might replace the Atlantic salmon in the Elbe River Basin.
England was probably the first country outside this original area into which huchen were introduced. In 1905 fertilized eggs were imported from Austria for angling and some of the hatched fry were released into the Thames River (Pölzl, 1910). Other fry were reared successfully in ponds and subsequently reproduced successfully (Pölzl, 1929). There are, however, few reports of specimens being caught by anglers and Marlborough (1963) suggested that some of the large trout caught recently in the Thames River may have been huchen. According to Wheeler and Maitland (1973), however, there is no indication that the huchen ever managed to establish itself.
Attempts were made to introduce huchen into the Rhine and Sarina Rivers in Switzerland in 1949–50 and 1965–67, respectively. Anglers initiated these introductions to obtain compensation for the disappearance of Atlantic salmon and to utilize dense stocks of undesirable Chondrostoma nasus. However, scientific circles were against this introduction (Steinmann, 1948; Brodbeck, 1953). Both rivers were repeatedly stocked with fry hatched from eggs imported from Czechoslovakia. Rhine stockings fully failed because no reproduction was observed and only four sub-adult fish of maximum weight 2 kg each, were caught of the 13 thousand fry planted. Natural reproduction was not observed in the Sarina River either.
Morocco imported fertilized eggs of huchen from Czechoslovakia in 1953 and in 1959. The fry were reared in ponds and after some time were introduced into some rivers of the Central Atlas (Rivers Fellate, Oum-er-Rbia and Guigou) hopefully to obtain a valuable game fish. The huchen showed extremely fast growth (15–16 month old fishes reached 46–57 cm total length) but naturalization has not been observed in any of the natural waters nor have attempts to breed this species in captivity met with any success.
More than 22 thousand fertilized huchen eggs of Yugoslavia origin were imported into Belgium in 1954, 1960 and 1961. More than six thousand yearlings measuring 10–18 cm were then planted into the River Lesse and an unknown lesser number into the Semois River (Maas River Basin). The huchen did not acclimatize in either stream although some specimens were observed in the Lesse River and a few specimens have also been caught by anglers (Timmermans, pers.comm.).
With the exception of the Black Orava River (Danube River Basin) huchen did not formerly occur in Poland. The first attempts to introduce the species were made at the end of the last century when it was planted into the Dunajec and Poprad Rivers in the Vistula River Basin. Here, it has naturalized and has persisted until the present time. Specimens from Polish huchen culture were then used in attempts to introduce this species into other streams of the Vistula and San River Basins as well as into the Drweca River, but until now no fish have become naturalized. The purpose of this introduction was to supplement Atlantic salmon and sea trout whose stocks are now very low (Witkowski and Kowalewski, 1980; Guziur, pers.comm., Witkowski, pers.comm.).
An introduction of huchen into the Usses River, France, was attempted in 1957. The stocking site was a left-bank tributary of the Rhone in Haute Savoie, whose upper reaches are inhabited by brown trout (Salmo trutta m. fario) and cyprinids among which Chondrostoma nasus is predominant. One year before introduction, the density of C. nasus was reduced by electro-fishing. A total of 50 thousand fertilized eggs were imported from Yugoslavia in 1957 and 1958 and after hatching the fed fry were released into the river. Stocking was repeated in 1959, and in 1960 when 10 thousand fertilized eggs were imported from Yugoslavia and the fry were released after hatching. Test fishing carried out in subsequent years confirmed the presence of huchen in the river and the young arising from natural reproduction were found in the spring and summer of 1963 (Vivier et al., 1964). Direct observation of natural spawning has been recorded in 1976 about 20 km upstream (Laurent pers.comm.). Angling for huchen was opened in 1965 and each year since several specimens have been caught, among which were some big fish weighing up to 15 and 25 kg (Svetina, 1967). Huchen penetrated into the Rhone from this tributary and one specimen was reported caught 50 km downstream from the confluence of the Usses and Rhone Rivers. According to Laurent (pers.comm.) the huchen is still to be found in the Usses River but only in small numbers because anglers are not interested in this species and the fishing season and size limit are no longer observed. The anglers have come to the conclusion that the huchen is unsuitable for such a small stream as the Usses and they are convinced that it destroys the spawning sites of trout and has thus been responsible for a decline of that species.
In 1963 a batch of 8 000 fertilized eggs of Yugoslavian origin was imported into Sweden. Advanced fry have been released into the Rexforsan River and the Indalsälven Reservoir. However, no huchen have either been caught or observed subsequently. In spite of this, there is a continuing interest in the introduction of this species into Swedish waters, especially into man-made lakes where it is hoped that it will be able to control the population of coarse fishes (Nilsson and Svärdson, 1963; Nilsson, pers.comm., Henricson, pers.comm.).
Twenty thousand fertilized eggs of huchen from Czechoslovakia (not from Yugoslavia as erroneously reported by Anon., 1969; 1973) were imported to Spain in 1968. Half was placed in the hatchery at La Coruña and some of the hatched fry were planted into the surrounding rivers, but no results were recorded. The rest of the fry were stocked into ponds and a brood is produced each year (Lobon-Cervia, pers comm.). The fry resulting from the second half of the import were introduced into the Tormes River near Salamanca (left-bank tributary of the Duero River). Here, four years after the introduction natural spawning was observed in 1972. Apparently the huchen has become naturalized here because it is regularly caught by anglers with records of specimens weighing up to 15 kg (Corredera-Martin, 1981). The growth of the huchen in the Tormes River seems to be very fast, as indicated by the following figures (Mondejar-Reyna, 1981): four-year old fish reaches 6.1 kg; five-year old - 9 kg; six-year old - 10.5 kg; and seven-year old - 11.9 kg. At present, the population density of the huchen is certainly low due to the closing of the spillway in the dam upstream. In 1976 the flow of the river decreased rapidly and mass mortalities of fish downstream were observed. The purpose of the introduction of the huchen to Spain was angling for a valuable trophy game fish.
For the sake of completeness, it is necessary to add that huchen has also been introduced into other countries. According to Skácel (1976) fertilized eggs were sent to the German Democratic Republic Finland, Bulgaria, Denmark and Canada. However, there is only information from Canada, where fertilized eggs were imported in 1966 and where fry were stocked into some rivers of Quebec (Crossman, 1968). The fate of the huchen in Canada is unknown (Lachner et al., 1970; Martin, pers.comm.).
There is very little direct quantitative information on the rate of predation of the common huchen either from the original area of its distribution or outside it. Pirozhnikov (1955) justified the lower fish yield in the Lena River in comparison with that in the Yenisei by the higher density of the taimen. It is also reported that the absence of some species (Coregonus muksun, Rutilus rutilus and Leuciscus idus) in some stretches of the Vilyui River (left-bank tributary of the Lena River) is due to the high density of predators, dominated by the taimen (Kirillov, 1962). The high density of C. nasus, dace (Leuciscus leuciscus) and chub (L. cephalus) in the Turiec River, Czechoslovakia, is reported to be correlated with the decline of the Danubian huchen (Novák, 1971); Bastl et al., 1976). Following the introduction of the huchen into the Usses River the C. nasus populations have declined and changes in the fish community structure have been observed. According to Vivier et al., (1964) and Svetina (1967) electro-fishing carried out in a limited part of this river in 1956 gave 8 t of fish, among which the C. nasus predominated. Four years after the introduction in 1961 2.8 t were caught; in 1962 - 1.9 t and in 1963 - 1.3 t of fish were caught in the same stretch. According to these authors the place formerly occupied by C. nasus and other cyprinid fishes (the chub and the barb) was gradually filled by brown trout, whose population density increased mainly in the weight groups of 100–300 g. According to anglers this species subsequently declined as the density of C. nasus and other cyprinids (which are the main food of the huchen - see Nagy, 1976) decreased and became less available for the huchen. Trout were the more available and predation on them increased accordingly. In one stretch of the Hornád River, Czechoslovakia, a transplanted and naturalized population of huchen had to be eradicated because the abundance of the brown trout and the grayling (Thymallus thymallus) significantly decreased (Skácel, 1976). Another anonymous author (1970) writes that the density of the huchen in the lower part of the Ammer River as well as in the upper part of the Isar River (basin of the Danube River) has had to be limited to protect brown trout and grayling. On the other hand, in the Tormes River, the population of the native Chondrostoma cyclolepis (the only fish inhabiting this stretch of the river) did not display any negative changes after the introduction of the huchen (Lobon-Cervia, pers.comm.). Unfortunately, there are no details on the density of either huchen or other fishes in any of the above cases.
From 38 attempts to introduce the huchen into new water bodies only eight (21 percent of the cases) were successful. According to information from individual sources the main reasons of the introduction failure may be as follows:
Ignorance of the ecology of the species with regard to its environmental requirements (Morocco);
Stocking at too early a developmental stage (fry) (e.g., Rhine in Switzerland), i.e., high mortality due to predation;
Insufficient numbers of fishes stocked (almost in all cases);
The short duration of introduction attempts - in almost all cases stocking was performed only once.
It is remarkable that attempts to introduce the huchen inside the original area of its distribution (transplantation) were more successful even though in these cases the same shortcomings were in evidence. It is furthermore not in agreement with Burmakin (1963) who writes that higher success of introduction is expected when any species is introduced into a water body outside its original area of distribution.
The reasons for the disappearance of the huchen after previously successful acclimatization lie in both the deterioration of the environment (in all cases studied increased pollution was evident) or eventually a change in the management philosophy which had led to the introduction in the first place (France).
The common huchen can be successfully introduced into waters from which it has been previously absent providing certain generally valid principles for the introduction of exotics (Burmakin, 1963; Karpevich, 1975) and some measures particular to this species are followed. These are:
The huchen may be transplanted into streams of the foot-hill zone with stony-gravel or gravel-sandy bottom, where the water temperature in summer months is not higher than 20°C, the dissolved oxygen does not fall below 8–9 mg/1, and the water is not polluted either by industrial, urban or agricultural waste. Those parts of a river where riffles alternate with bigger and deeper pools, where the flow is branched by islands, the banks are overgrown with shrubs and trees and interrupted by the mouths of tributaries are to be preferred. Reaches selected should be sufficiently long and the zone of the of foothill brooks with possible spawning grounds should be accessible. The overall length of a reach should be about 20 km.
Introduction should be preceded by limnological investigations aimed at defining the hydrological regime and hydrochemical properties of a water, and evaluating the bottom fauna and fish fauna quantitatively and qualitatively. Sufficient amounts of invertebrates and coarse fish should be present in a chosen reach. Streams which are densely populated by the brown trout, grayling or other valuable game fish should be avoided.
Prior to the first introduction of the huchen, it is desirable to reduce the number of native fishes and particularly of some predators (pike, burbot) and abundantly-occurring coarse fishes (in European conditions these are chub, dace, nase, perch). Big specimens of brown trout should also be removed. The reduction should be selective as numbers of big specimens above 100 mm of the total length) only should be restricted.
Only healthy fingerlings (minimum six-months old) should be used for stocking. If only fry are available these should be planted into the side tributaries of the chosen section of stream or into the uppermost part of it. In this eventuality the relevant stream or section should be completely deprived of all native fishes.
Stocking should be repeated each year during the first four-six years until specimens from the first introduction reproduce.
Angling or fishing should be prohibited in the stream during the whole course of introduction. Particularly in streams where brown trout occur because here anglers frequently mistake young huchen for brown trout.
The situation in the whole of the stream into which huchen have been introduced should be closely monitored for the presence and density of huchen, growth, health condition, diet and sexual maturation, migrations and also with regard to the time and place of spawning.
By giving the principles for introduction of huchen, it does not mean that the author is advocating the transfer of this species indiscriminately The huchen should be introduced only into rivers where it occurred formerly (reacclimatization) or into rivers which were originally not inhabited by it, but which are inside the original area of its distribution (transplantation). In these cases introduction is justified as a measure aimed at the rescue of this species before its extinction.
It is true that because of its specific environmental requirements the huchen is limited only to some reaches of rivers and it is therefore possible to consider its introduction outside its original area of distribution. However, the benefits of such introduction should be carefully judged. The huchen, as the top predator of the ecosystem of foothill rivers, may be used to control populations of overcrowded forage species, however, it is unable to form dense populations and, therefore, is unable to replace diadromous salmonids such as the Atlantic salmon or the sea trout. Furthermore, because of the present state of the water quality in European rivers the huchen is able to populate only relatively short portions of any river. The contribution of huchen introduced outside its natural range will probably be dubious with high costs and a possible negative effect upon the populations of native fishes.
I have a great many acknowledgements to make. In addition to many friends in Czechoslovakia, I have to mention only a few of the foreign colleagues who sent me information and data on the introduction of the huchen in their countries. They are as follows: Mr. J. Bél, Seenforschungslaboratorium der EAWAG/ETH Kastanienbaum, Switzerland; Dr. J. Guziur, Instytut Ichtiobiologii i Rybactwa ART Olsztyn, Poland; Dr. P. Laurent, Station d'Hydrobiologie Lacustre INRA, Thonon-les Baines, France; Dr. J. Lobon-Cervia, Centro de Zoologia Aplicada INCN, Madrid, Spain; Mr. N.V. Martin, Ontario Ministry of Natural Resources, Maple, Canada; Ing. C. Mondejar-Reyna, Seccion de Hidrologia INCN, Madrid, Spain; Dr. N.A. Nilsson, Institute of Freshwater Research, Drottningholm, Sweden; Dr. S.U. Qadri, University of Ottawa, Ottawa, Canada; Dr. J.A. Timmermans, Station de Recherches des Eaux et Forets, Greonendaal, Belgium, and Dr. A. Witkowski, Uniwersytet Wroclawski, Wroclaw, Poland.
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Fig. 1 Introductions of the huchen in Europe and North Africa:
1 - Introductions; 2 - Autochthonous distribution of Danubian huchen; 3 - Autochthonous distribution of taimen/its western part only. According to Holčík et al., 1981 (slightly modified)