Finnish Game and Fisheries Research Institute
Laukaa Fish Culture Research Station
P. Tuunainen and E. Ikonen
Finnish Game and Fisheries Research Institute
The objectives of fish stocking in Finland have been to compensate for the damage done by hydro-construction, water level regulation and water pollution, particularly noticeable in the case of river-spawning fish species; to maintain, strengthen and improve the quality of fish populations; and to create entirely new fishing opportunities.
Fish stockings have increased considerably since the fifties. In 1980, stockings of 21 fish species (15 native and 6 introduced) and one crayfish species were carried out. In that year, 196.3 million newly-hatched fish were stocked, of which about 88 percent were whitefish (Coregonus sp.) and 9 percent were pike (Esox lucius). The number of cultivated, one-summer old or older stocked juveniles was 34.4 million individuals. The vast majority of these (83 percent) were also whitefish. The next most frequently stocked were brown trout and sea trout (Salmo trutta m. lacustris and S. trutta m. trutta), pike, Atlantic and landlocked salmon (S. salar and S. salar m. sebago) and grayling (Thymallus thymallus). In the near future in Finland, the obligation to stock salmon, sea trout and brown trout and whitefish in particular, will increase considerably because of the necessity to compensate for the damage caused by construction in the water systems.
Stocking of newly-hatched fish have been most successful primarily in waters in which the natural reproduction of a species has been disturbed, as well as in some cases in the introduction of certain species to new locations. However, such stockings have evidently not significantly improved the catch in waters where the species is already reproducing in sufficient quantities. A well planned and executed stocking with sufficiently large juveniles has usually had good results in water suitable for the species. It has proved to be difficult to increase the profitability of fisheries, by stocking into waters whose quality has deteriorated as a result of hydro-construction, lake water level regulation or pollution. This paper deals species by species with the fish and crayfish stockings carried out in Finland, and evaluates their results.
En Finlande, les objectifs du repeuplement sont les suivants: compenser les dommages occasionnés par la construction d'ouvrages hydro-électriques, par la régulation du niveau des eaux et par la pollution aquatique, dommages particulièrement graves dans le cas des espèces frayant dans les cours d'eau; renforcer les populations de poissons et en améliorer la qualité; créer des possibilités de pêche entièrement nouvelles.
La pratique du repeuplement s'est considérablement développée depuis les années cinquante. En 1980, les eaux ont été repeuplées avec 21 espèces de poisson (15 indigènes et 6 exotiques) et une espèce d'écrevisse; on a utilisé 196,3 millions de poissons nouvellement éclos, dont environ 88 pour cent de poissons blancs (Coregonus sp) et 9 pour cent de brochets (Esox lucius). Le nombre de juvéniles d'élevage, d'un été ou plus, utilisés pour le repeuplement atteignait 34,4 millions d'unités. Ici aussi, il s'agissait dans la grande majorité des cas (83 pour cent) de poissons blancs. Parmi les espèces les plus utilisées ensuite, on citera la truite (Salmo trutta m. lacustris et S. trutta m. trutta), le brochet, le saumon atlantique et le saumon des eaux intérieures (S. salar et S. salar m. sebago) ainsi que l'ombre commun (Thymallus thymallus). Dans un proche avenir, il faudra faire un effort de repeuplement encore plus important, notamment en ce qui concerne le saumon, la truite et le poisson blanc, pour compenser les dommages occasionnés par les ouvrages construits sur les cours d'eau.
Le repeuplement avec des poissons nouvellement éclos a été particulièrement efficace dans les eaux où la reproduction naturelle d'une espèce avait été perturbée ainsi que dans certains cas d'introduction. Evidemment, ces opérations n'ont pas entraîné de forte augmentation des captures dans les eaux où la reproduction était déjà satisfaisante. Les opérations bien planifiées et bien menées de repeuplement avec des juvéniles suffisamment développés ont en général donné de bons résultats dan les eaux qui convenaient aux espèces utilisées. On a observé qu'il était difficile d'accroître grâce au repeuplement la rentabilité des pêches dans les eaux dont la qualité s'était dégradée par suite de la construction d'ouvrages hydro-électriques, de la régulation du niveau des lacs ou de la pollution. Les auteurs examinent espèce par espèce les opérations de repeuplement effectuées en Finlande avec des poissons et des écrevisses et en évaluent les résultats.
The inland waters of Finland cover 31 613 km2, which is about 9.4 percent of the total area of the country. There are over 60 000 lakes, 17 of which have a surface area of more than 200 km2. Typically, the lakes are joined through sounds and short streams forming long water courses. The total length of the rivers exceeds 20 000 km.
The lakes are shallow, the average depth being 7 m. Most of the lakes (86 percent) are oligotrophic and the eutrophic lakes (14 percent) are generally located in the south and southwest, in clay-soil areas.
Technological and economic development have brought with them marked changes in the condition of the Finnish lakes and rivers. The damming of rivers, clearing of obstructions, dredging, flood control measures, regulation of water levels and stream flows, water pollution, timber floating and forest ditching have all had a deleterious effect. Some 20 percent of the total surface area of Finnish lakes is significantly affected by waste water, and the water level in most large lakes is being regulated for purposes of hydro-electric power generation. About 1 400 km2 of the coastal waters have also been changed from their natural state. The major portion of the largest rivers, about 9 000 km combined length, is at best only in satisfactory condition from the point of view of fisheries.
The stocks of many valuable river-spawning migratory fish species have been seriously damaged by the river damming and construction operations. Concerning the Finnish rivers flowing into the Baltic, salmon (Salmo salar) are still found only in three rivers. The natural salmon smolt production from Finnish territory to the Baltic nowadays amounts to less than 350 000 individuals instead of the 2.5 million that existed when the waters were in their natural state. The number of spawning rivers for the landlocked salmon, sea trout (S. trutta m. trutta), brown trout (S. trutta m. lacustris), migratory whitefish (Coregonus lavaretus and C. muksun) and lamprey (Petromyzon fluviatilis) have also declined dramatically.
The construction of hydro-electric power plants, regulation of water levels and other such activities, have decreased in Finland in recent years, and the water quality has been improving through more effective waste-water treatment.
Under the Fisheries Act the owners of fishing waters are responsible for the conservation and management of fish stocks. Waters within village limits are generally jointly owned by local landowners, those outside the villages by the State. Currently about 85 percent of all inland fishing waters are privately owned. Fishing rights are generally held by the owners, each landowner's share and fishing rights in a jointly-owned water area depending on the size of his estate (Munne, 1980; Sjöblom et al., 1980).
Under the Fisheries Act (coming into force on 1/1/83) the water owners from a village will be obliged to form a fishing commune to define the extent of fishing rights for each shareholder. These obligations can, however, be transferred to a larger administrative body, the so-called “Fisheries Area”.
Government responsibility for both inland and marine fisheries and their management in Finland is vested in the Ministry of Agriculture and Forestry. Most State-owned waters are administered by the National Board of Forestry. There are three government-sponsored organizations for fisheries and their management: the Federation of Finnish Fisheries Associations, the Federation of Finnish Recreational Fishermen's Associations and the Finnish Fish and Game Association.
In the management of fish populations in Finland, fish stocking plays a central role. Through stocking, fish populations already present are preserved and strengthened, and exhausted stocks are replaced with new ones. In acclimatization stocking a new fish species is introduced to a watercourse; in supplementary stocking a species already living in the watercourse but diminished in numbers is stocked; in transfer stocking mature fish are transplanted from one body of water to another; in repetitive stocking species not reproducing in natural conditions are stocked. Obligatory stockings, which are made pursuant to decisions in Water Courts, are aimed at the repair of damage caused to fish stocks by hydro-construction or other changes in water courses (Sjöblom et al., 1980).
Fish stockings in Finland are primarily financed by fishing communes in privately owned waters, the State and others, e.g., hydro-electric power companies, cities, industry, etc., who make mostly obligatory stockings (see Salojärvi, 1982).
Government fish culture is organized by the Finnish Game and Fisheries Research Institute and its ten aquaculture stations. The latter do not generally sell juvenile fish but use them for stocking in places where wild stocks have become depleted and are in danger of extinction, for ensuring fish farms of a steady supply of wild fish eggs, or for research and trial purposes. In addition, fish are released in the sea and the larger inland water bodies for general management purposes.
Fish stocking has increased considerably since the fifties. Since 1978 the Finnish Game and Fisheries Research Institute has prepared annual statistics which have included details concerning the number of juveniles released, the number of established fish hatcheries and their capacities. These statistics are obtained through a questionnaire sent out to all fish farms (Sumari and Eskelinen, 1980). Data abstracted from the fish-culture statistical report and relating to the stocking of juveniles over the period 1978–80 are presented in Tables 1 and 2.
The stocking of all significant species over the period has increased. In 1980, stocking of 21 fish species (15 native and 6 introduced) and one crayfish species was carried out. In that year, 196.3 million newly-hatched fish were stocked, of which about 88 percent were whitefish (Coregonus sp.) and 9 percent were pike (Esox lucius). Newly-hatched whitefish and pike are released mainly because eggs of these fish are easily come by and techniques for their incubation are known. The number of newly-hatched juveniles released depends to a large extent on random factors, and varies considerably.
In 1980, the number of cultivated, one-summer or older stocked juveniles was 34.4 million individuals. The vast majority of these (83 percent) were also whitefish. One-summer whitefish, of length approximately 10 cm and introduced into inland waters, amount to six fish per hectare of Finnish lake. The next most frequently stocked were brown and sea trout (Salmo trutta m. lacustris and S. trutta m. trutta), pike, Atlantic and landlocked salmon (S. salar and S. salar m. sebago) and grayling (Thymallus thymallus).
The value of juveniles produced for release by fish hatcheries and natural food ponds was approximately 25 million FIM (U.S.$ 6.3 million) in 1980. The cost of stocking per water hectare of inland waters and of the coastal fishing zone was approximately 2.5 FIM.
2.2.1 The whitefish (Coregonids)
The total number of one-summer whitefish are as follows for the four most important species:
|Coregonus lavaretus (L.) s. str.||30–55 percent||(8 876 000 ind. in 1980)|
|C. muksun (Pallas)||20–30 percent||(7 986 000 ind. in 1980)|
|C. peled (Gmelin) s. Berg||10–20 percent||(5 164 000 ind. in 1980)|
|C. pidschian (Gmelin)||5–10 percent||(3 109 000 ind. in 1980)|
Small numbers of C. oxyrhynchus L. have also been stocked.
C. lavaretus is raised most commonly in northern Finland, from the largest rivers of which cultivated strains have also originated (Salojärvi, 1982a, 1982b).
Most of the stockings with C. pidschian have been carried out in regulated Lake Inari area. Only the Lake Inarijärvi strain has been used in fish farming. C. muksun is raised and employed for stocking purposes throughout the country. Natural stocks of the species are meagre, and lack of eggs has limited cultivation. The raising of brood fish in fish farms has increased the availability of eggs and the species has been stocked more frequently. C. peled was introduced to Finland in 1965 and it has increased rapidly in the management of lakes in south and central Finland where whitefish have not previously existed and also in eutrophicated lakes (see Westman and Tuunainen, 1983).
In addition to the species mentioned above, hybrid whitefish forms are cultivated. Annually, large numbers of juveniles are transferred from north Finland to the southern parts of the country, where the demand exceeds the supply.
The hatching of vendace (C. albula) eggs is spasmodic and only newly-hatched juveniles are stocked.
2.2.2 Atlantic salmon, sea trout and brown trout
The objective of the stocking of Atlantic salmon smolts is to compensate for the damage caused by hydro-construction. The stocked numbers of smolts have greatly increased over the last few years and will increase even in the near future with the implementation of certain large-scale stocking schemes based on decisions in Water Courts. Stocking of Bothnian Bay is carried out using the three indigenous salmon strains from rivers draining into the area still left. The original salmon strains from the rivers of the Bothnian Sea and the Gulf of Finland have disappeared and strain from the River Neva (U.S.S.R.) is being used for stockings in these.
Sea trout and brown trout are cultivated in all parts of the country and are employed in the management of both the inland waters and the coastal districts. The number of migratory juveniles produced for stocking purposes is larger than the reduction in numbers of wild juveniles. A large proportion of trout releases are made in connexion with voluntary management of fish stocks. Several different strains of sea trout and brown trout are used in production and hence the species compete for the same space at fish farms.
2.2.3 Other salmonids and grayling
In addition to Atlantic salmon and sea trout and brown trout, salmonid fishes used for stocking are landlocked salmon, char (Salvelinus alpinus), lake trout (S. namaycush), brook trout (S. fontinalis), grayling (Thymallus thymallus) and rainbow trout (Salmo gairdneri). Some 50–150 thousand landlocked salmon smolts are produced annually. The cultivated strain is a relict form from the Vuoksi watercourse (Seppovaara, 1962; Westman, 1970). Juveniles are released in the Vuoksi watercourse and in the northernmost Finnish lakes. Char and lake trout are mainly cultivated and stocked in north Finland. Juveniles from the native char strains are released annually to the extent of 50 000 individuals.
A more important species for the management of fishing waters is the North American lake trout, which has become acclimatized to Finnish conditions (Mutenia, Simola and Tuuniainen, 1983). The numbers of this species stocked are 50 000–300 000 specimens annually. The production numbers for the brook trout and splake, both originating from North America (Westman and Tuunnainen, 1983), are far smaller than the former species.
Cultivation of grayling, as with char and lake trout, is concentrated in the northern part of the country. Annual production of one-summer juveniles for stocking purposes has been on average 500 000 individuals.
The stocking of natural waters with rainbow trout is not carried out very much, and is primarily for “put and take” fishing. The rainbow trout is the only species of significance in food fish production (Westman and Tuunainen, 1983).
2.2.4 Pike, perciforms and cyprinids
Pike (Esox lucius), perciforms and cyprinids are cultivated in Finland far less commonly than salmonids. Cultivation is concentrated in south Finland. Newly-hatched pike fry are stocked annually to the extent of around 20 million individuals. Eggs are obtained from brood fish caught on the spawning grounds in the wild. A large proportion of pike eggs are incubated in temporary field hatcheries.
Pike-perch (Stizostedion lucioperca) is the only perciform cultivated, the annual production (below 100 000 individuals) of one-summer old fingerlings satisfying only a small part of the demand. An obstacle to greater production is the lack of eggs.
There is little cultivation of cyprinids. A few score thousand juveniles of bream (Abramis brama), carp (Cyprinus carpio) and tench (Tinca tinca spp.) are stocked annually (Ahlfors, Kummu and Westman, 1983; Westmand and Tuunainen, 1983).
The main production methods for juveniles of the more important cultivated species are presented in Table 3. In whitefish stocking, one-summer fingerlings are used and these are produced almost entirely in large natural food ponds up to 200 ha in size. The eggs required for raising whitefish migrating into the sea are obtained for the most part from brood fish caught in the wild. In fresh water, brood fish, river-spawning forms, have had to be reared artificially. Brood fish have been raised extensively on natural food in small lakes but recently an increasingly large number have been raised by intensive cultivation methods at fish farms.
Eggs which are incubated in jars hatch in May–June and fry are released in the ponds as soon as they hatch. Production per hectare is an average 50–60 kg during the summer. Variations in production capacity owing to pond type and local climatic differences are great. Increasing production capacity by fertilization and additional feeding has been attempted. Over 90 percent of the total surface area (4 700 ha) of natural food ponds throughout the whole country is used for whitefish cultivation.
The transference of whitefish juveniles from natural food ponds to stocking waters is in many cases arranged so that the fingerlings are carried by the water to the site when emptying the pond. For transfer stockings, fish are either collected in a catching box sited in the drainage ditch or are caught in the pond in small mesh trap nets.
Cultivation methods for grayling and pike-perch differ very little from the above. Eggs of both species required for raising purposes are mainly collected from the wild. Pike-perch are stocked in natural food ponds either as eggs, as newly-hatched fry or as feeding juveniles.
Smolts and juveniles of salmon, trout and other predatory salmonids are produced principally by the conventional intensive cultivation method at fish farms. As a result of the drastic weakening of wild salmon stocks, the acquisition of eggs from wild spawning is unreliable as well as insufficient to meet needs. Hence, the amount of eggs required for stocking purposes has been ensured by establishing brook fish stocks at fish farms. In order to prevent genetic weakening of stocks and domestication in farm conditions, brood fish shoals are as far as possible raised from wild-collected eggs.
Incubation trays are generally employed for incubating the eggs of salmonid fishes. For the first year of rearing the fish are generally raised in rearing halls in small plastic tanks. The most common site for the second year of rearing are largish earthen ponds with continuously changing water. Swedish-style concrete circular tanks are also utilized to a certain extent. The most common age for stocking is two years, but in northern Finland three-year old smolts are also released. For feeding purposes factory-produced dry feed is employed almost exclusively.
Trials have been initiated in raising juveniles in the warm-water effluent of power stations (Tuunainen et al., 1981). New techniques, including water recirculation, heat exchange using exchangers and pumps, and the pre-treatment and post-treatment of water, have recently been adopted particularly at the incubation and fry stage.
The number of fish farms in Finland increased during the seventies. Developments during the period 1978–80 regarding the number of fish farms and various production centres are presented in Table 4.
Fish farms are owned by the State, fishery associations, private persons and fish enterprises, or by wood processing, power and similar companies. The State fish cultivation stations produce eggs and juveniles for further rearing at other farms, and the State also raise fish for their own stocking programmes, which are carried out for research purposes, for safe-guarding the supply of eggs, or for supplementing fish stocks in State-owned water bodies. The fish farms owned by the fisheries associations and companies produce juveniles for their obligatory stockings or for voluntary fish stock management purposes. The production of fish for stocking by private commercial fish enterprises is marketed for voluntary management of fishing waters. An appreciable proportion of juveniles needed for obligatory stocking purposes are produced under contract at private commercial fish farms.
In terms of specializations, the fish farms vary considerably. Farms involved solely with hatching are located near the places from which eggs can be collected from wild brood fish. Private natural food pond enterprises are not generally involved in hatching operations. The largest commercial enterprises are specialized in the production of one stage or another. The state's central fish cultivation stations are involved in the most comprehensive activities of all covering brood fish raising, egg hatching and juvenile raising, of many species and strains using intensive cultivation and natural food pond methods.
A large proportion of fish-farm rearing space is given over to the raising of rainbow trout for food. Net cages and net enclosures are utilized almost entirely for this purpose. The production of rainbow trout in Finland in 1980 was almost 5 000 t. Rainbow trout is marketed after the third rearing period, when it weighs 0.5–1.5 kg.
Hatching jar or cylinder capacity has not increased significantly over recent years, in spite of the fact that the amount of stocking has increased. Owing to the wide variation in the quantities of eggs obtained from the wild, there is an excess of incubation space when compared to average years. It has thus been possible to incubate more eggs by raising the degree of utilization. The increase in hatching trough space for salmon, trout, rainbow trout and char is keeping pace with the growth in the number of eggs requiring incubation.
The rearing space at fish farms has kept pace with the increase in production. The increasing intensification usage at fish farms is leading to wider use of circular tanks. Water conservation aspects also affect the type of ponds and basins utilized. Waste arising through fish cultivation operations must be collected in a more controlled manner as well as more quickly than previously. This has resulted in attempts at making ponds self-cleaning. The monitoring guide issued by the water protection authorities recommends that net-cage establishments be prohibited in inland water districts.
Natural food pond cultivation increased rapidly throughout the seventies. The size of the ponds, their location and number of ponds per station depend on the nature of places suitable for use as ponds. The average size of ponds is greatest in northern Finland.
The distribution of salmonid and coregonid juvenile production in 1978 is illustrated in Fig. 1. The principal area for production is northern Finland, where the adverse effects of constructions in inland waters on the natural production of these fish are at their strongest. The concentration of production in northern Finland is greatest with those species the juveniles of which are raised in natural food ponds. This results from the abundance of sites suitable for use as fish ponds and also from the fact that the State grants more money from its employment fund for pond construction in northern Finland than for the same purpose in the southern part of the country. Several non-salmonid species utilized in stocking schemes live at the extreme northern limits of their range in Finland and these are raised and employed for stocking in southern Finland.
In order to investigate the results of fish stocking, large numbers of fish are tagged in Finland annually. The usual form of tagging is by means of the Carlin tag. Table 5 presents the number of fish tagged with Carlin tags in Finland during the period 1978–80. During the last couple of years one-summer whitefish in particular have been marked by nose-tagging.
The coregonid species used for stockings in Finland in the last few years are Coregonus pidschian (Gmelin), C. lavaretus (L.), C. oxyrhynchus (L.), C. muksun (Pallas), G. peled (Gmelin) and C. albula (L.). C. pidschian, a benthos feeder in the lakes of Finnish Lapland, has been released into the lakes of northernmost Finland. For example, in order to compensate for damages which have been caused to the fishery on Lake Inari by water level regulation, one million autumn fingerlings per year will be stocked. A monitoring programme for the evaluation of the results of the stocking scheme is currently underway. The results are unknown at present since full-scale stocking has been carried out only over the last few years. The mean recruiting age (t) for C. pidschian in Lake Inari is 4–5 years (see Toivonen et al., 1981).
C. lavaretus, the migratory whitefish, is the species which has been stocked in highest numbers in Finland. Most of the newly-hatched larvae have been stocked into the sea but also into the lakes in smaller numbers. In inland waters mainly one-summer old fingerlings have been used. In his report for this symposium, Salojärvi (1982) deals with the results of stockings with this species. The results from stocking with fry in inland waters have usually been quite poor (average catch 2–4 kg/1 000 stocked in eight lakes) but with autumn fingerlings quite satisfactory (average catch 120–150 kg/1 000 stocked in eight lakes). Catches based on stocks maintained by stocking with about 1–3 kg fingerlings/ha/year have been reported from nothern Finland.
C. oxyrhynchus, a whitefish species typical to the lake district of Finland, has been recently used for stocking only in small quantities and the results of stocking with autumn fingerlings are unknown. There is at least one remarkably successful stocking with this species. Lake Pyhäjärvi (154.5 km2), in southwest Finland, was stocked with fry of C. oxyrhynchus in 1921–23 after a previous attempt with C. lavaretus fry in 1910–13 failed. C. oxyrhynchus established a permanent stock in the lake and the annual catches have been over 100 t.
C. muksun, a plankton feeder from eastern Finland, is one of those whitefish species which will become more and more common in fisheries management in Finland. Numerous practical experiences with this species are very promising. However, only a few studies have been made on it. In small forest lakes in southern Finland it did very well (see Hakkari et al., 1983; Pruuki, Pursiainen and Westman, 1983) feeding on zooplankton and giving an annual net production of 2 kg/ha in one experimental lake and 23 kg/ha in another.
C. peled, a Siberian plankton feeder, has been introduced in a number of Finnish lakes after its importation in 1965. There is at least one very successful introduction with newly-hatched larvae of C. peled. This is the Lokka reservoir (maximum area 417 km2) in Finnish Lapland, where the catch was 15 kg/1 000 introduced fry (see Salojärvi, 1982). Also stocking attempts with fingerlings have given fairly good results. In the Lokka reservoir, the catch has even been 12 percent (10 t) of the total catch (see Westman and Tuunainen, 1982). In small forest lakes in southern Finland it has given good results too, the annual net production being 4 kg/ha in one experimental lake and 31 kg/ha in another (see Hakkari et al., 1982; Pruuki, Pursiainen and Westman, 1983).
C. albula, the vendace or cisco, is a plankton feeder. Numerous new stocks have been established by transplantation of adult fish or fry of vendace mainly at the end of the 19th and the beginning of the 20th century. Stocking of lakes with newly-hatched larvae has been very common up to the seventies because the eggs have been readily available and their incubation is easy. On the basis of practical experiences, it is commonly believed nowadays that stocking of large lakes with vendace fry is unprofitable.
Reared salmon smolts have been released into the Baltic Sea in Finland since 1959, sea trout smolts since 1962 and brown trout in inland waters since the fifties. The results of stockings have been followed by means of tagging experiments. The tag most commonly used was the Carlin tag. The mean number of tagged salmon in each experimental group during the seventies was in the main about 1 000. In experimental groups of sea trout and brown trout there have generally been about 500. Salmon stocking has been done mainly in spring when the water temperature in the river approaches 10°C. Salmon smolts have been two-three years old. Sea trout and brown trout stockings have also mainly been in the spring though quite a large proportion have also been released during the autumn, when the age of the fish has been two summers.
Salmon smolts have been released into the estuary or its surroundings. However, some experiments have been carried out with stocking salmon quite far from the coast and from the estuary. For instance, in the Archipelago Sea salmon have been released into the coast of the Aland Isles in brackish water. Freshwater resources in the area are severely limited.
Sea trout stockings have been carried out mainly in the coastal area. Some of the smolts have been transported further from the coast by boat and a smaller part have been released into the rivers or river mouth surroundings.
Brown trout smolts released into inland waters have been mainly dispersed to the shores of lakes. However, some brown trout stocking has been done in the rivers flowing into lakes and a small proportion in rivers flowing into the Baltic Sea.
Sea trout and brown trout stocking has been made over almost the same period.
The mean length of wild salmon smolts in the River Simojoki has been 15.5 cm. The mean length of salmon smolts employed for stocking has been about 14 cm. Sea trout and brown trout stockings have mainly been done using smolts of 18–20 cm (mean). However, in the regulated lakes bigger smolts (about 25 cm) have been used.
The migration pattern of salmon of the northern strains differs from that of the southern ones. Salmon strains of the rivers flowing to the Bothnian Bay area are wide-migrating. Most of these fish migrate to the southern Baltic proper. Southern stocks, for instance River Neva stock released from the estuary of the River Kymijoki which flows into the Gulf of Finland, do not migrate so far. On the basis of tagging results, only 14 percent of all recoveries have been made outside the Gulf of Finland. In comparison with River Oulujoki stock in the Bothnian Bay area, the majority of recoveries have been made in the Baltic proper. In the Bothnian Sea area tagged salmon of River Neva stock and River Iijoki stock (Bothnian Bay) were released in the estuary of the River Kokemäenjoki. Recoveries of River Neva stock were mainly made in the Bothnian Sea area. Outside this area only 12 percent of all recoveries were caught. River Iijoki stock migrated mainly into the Baltic proper and less than 50 percent were caught in the Bothnian Sea area.
Sea trout do not migrate to the same extent as Atlantic salmon. The majority of recoveries of sea trout taggings have been made within 100 km from the release point (Toivonen and Tuhkunen, 1975). It has also been observed that sea trout migrate with the current in the Gulf of Bothnia. The current flows along the Finnish coast in a northerly direction and along the Swedish coast in a southerly direction. Sea trout taggings in the northern part of the Bothnian Bay area have revealed that more than 10 percent of all recoveries have been made from the Swedish coast to the Bothnian Bay, where fish have migrated with the current by following the coastline.
The migration area of brown trout is also not so extensive as that of landlocked salmon. In the watercourses brown trout mainly stay in or near lakes where they have been released in contrast to landlocked salmon which migrate several hundred kilometres along the watercourse.
A diminishing trend in yields per 1 000 released salmon smolts since 1972 has been very obvious. The 1972 summer was exceptionally warm and this might explain the good results of stockings. Later years have, however, given progressively worse results. The reason might be less favourable weather conditions. However, the total catch of salmon in the Baltic Sea has not decreased in a similar way as tagging results show. It is obvious that stocking has given poor results only through tagged fish. Untagged fish must have given much better results than the tagging results suggest. The reason seems to be dependent on taggings and one important fact is the increase in numbers of unreported tags. During the last three-four years limitations on salmon fishing have been demanded because the wild stock is in danger of being destroyed due to the lack of spawners. These plans to limit salmon fishery might have resulted in the fisherman being any more eager to recover tags because they are afraid of catch limitations. However, a similar trend is also observable from sea trout tagging results, but no plans have been made to limit sea trout fishing.
Salmon stocking has mainly been carried out in the Bothnian Bay area in the sixties and seventies. That is the reason the best tagging series are available from this area. The results of tagging show that the mean yield per 1 000 released smolts was about 330 kg in 1970. The lowest stocking result has been obtained from the smolt year-class 1972 when the result was about 830 kg. After this year the results have diminished rapidly. In 1975 the result was a little less than 400 kg and in 1978 a trifle over 150 kg.
The results of stocking of sea trout in the Bothnian Bay area also follow this descending trend. However, there is one exception. The best year was not 1972, when the result was about 150 kg, but 1973 when the result was 230 kg. Since then the results have fallen even as far as 60 kg in 1977. Sea trout tagging on the other parts of the Finnish coast do not form a continuous series for comparison purposes. However, it can be observed that the mean yield per 1 000 released sea trout was about 300 kg in 1972 in the Gulf of Finland but in 1976 yield had fallen to a level of 190 kg. A similar trend can also be found in sea trout tagging in the region of the Archipelago Sea and the Bothnian Sea.
Stockings with brown trout produced slightly better results in the sixties than in the seventies. For instance, in the Vuoksi watercourse, the mean yield per 1 000 stocked brown trout was 205 kg in the sixties. However, in the seventies it was only 80 kg. In brown trout stockings it is also possible to discover similar evidence of better results in 1972 and 1973 just as in the salmon and sea trout taggings (Toivonen et al., 1983).
The results of tagging salmon, sea trout and brown trout have shown that smolt releases during the spring give better results than those made in the autumn. In the Simojoki River in the Bothnian Bay area it has been observed that smolt migration of salmon stocks when the temperature in the river rises to 10°C. The river water temperature has been used as a guide for timing the salmon stocked.
Introduction of lake trout in natural waters in northern Finland have given positive results, and in Lake Inari the lake trout catch is already about 10 percent of the total catch (Mutenia, Simola and Tuunainen, 1983).
Stocking of brook trout and splake has met with little success, and current interest in the farming of these species is very little (see Westman and Tuunainen, 1983).
There are no known investigations on the stocking of newly-hatched pike, but their significance in increasing pike catches on the basis of the observed practical results, has been very little. In stocking activities, there is an increasing tendency to release 3–5 cm long juveniles cultured in natural food ponds. At present, no definite details relating to the results of stocking are available.
Regarding the transfer stocking of mature fish, it has proven possible to acclimatize pike-perch in numerous waters. According to reports (Toivonen et al., 1981) pike-perch exists in 476 Finnish lakes. It was regarded as occurring naturally in 129 of these, and solely as a result of stocking in 94 places. Stocks which had been reinforced by stocking, or whose origins were unknown, occurred in 79 lakes. Pike-perch had been released without effect in 174 lakes. The cultivation and stocking of one-summer pike-perch juveniles is on the increase in Finland. In practice, stocking has often been shown to have produced good results.
The best results with carp have been obtained with two or three-year old juveniles at least 20 cm in length and weighing circa 150 g or more. In inland waters, the rate of return of carp tags has varied between 0–32 percent, which in terms of a catch means 0–336 kg/1 000 stocked individuals. However, no economically profitable results have so far been obtained from stocking (Ahlfors, Kummu and Westman, 1983).
Stocking of newly hatched fish has been most successful primarily in waters in which the natural reproduction of a species has been disturbed, as well as in some cases where certain species have been introduced to new locations. However, such stocking has evidently not significantly improved the catch in waters where the species is already reproducing in sufficient quantities.
A well planned and executed stocking with sufficiently large juveniles has usually had good results in water suitable for the species. It has proved to be difficult to increase, by stocking, fishery profitability in waters whose quality has deteriorated as a result of hydro-construction, lake water-level regulation, or pollution.
Ahlfors, P., P. Kummu and K. Westman, 1984 Introduction of carp (Cyprinus carpio (L.)) in Finland. EIFAC Tech.Pap., (42) Vol.2:299–312
Hakkari, L. et al., 1984 Food supply of native whitefish (Coregonus muksun) and the introduced whitefish (C. peled) stocked in the same small forest lakes in southern Finland. EIFAC Tech.Pap., (42)Vol.1:109–22
Mutenia, A., O. Simola and O. Tuunainen, 1984 Results of lake trout (Salvelinus namaycush) stockings in Finland in 1957–81. EIFAC Tech.Pap., (42)Vol.2:381–91
Pruuki, V., M. Pursiainen and K. Westman, 1984 A study of the growth and production of the native whitefish (Coregonus muksun (Pallas)) and the introduced whitefish (C. peled (Gmelin)) stocked in two small forest lakes in southern Finland. EIFAC Tech.Pap., (42)Vol.1:91–108
Salojarvi, K., 1982 Results and profitability of whitefish (Coregonus lavaretus) stockings in north Finland. Paper presented to the EIFAC Symposium on Stock enhancement in the management of freshwater fisheries. Budapest, Hungary, 31 May–5 June 1982. rome, FAO, EIFAC/XII/82/Symp.10 (mimeo)
Seppovaars, O., 1962 Zur Systematik und Okologie des Lachses und der Forellen in den Binnengewassern Finnlands. Ann.Zool.Soc.Vanamo, 24:1–86
Sjoblom, V. et al., Fisheries. Atlas of Finland, appendix 233:11–21. Helsinki
Sumari, O. and U. Eskelinen, 1980 Kalanviljely Suomessa vuonna 1978. Suomen Kalastualehti, 87:68–72
Toivonen, J. et al., 1981 (Selection of the minimum mesh size for gill nets in the fishery of Lake Inarinjarvi). Riista- ja kalatalouden tutkimuslaitos, kalantutkimusosasto. Tiedonantoja, 17:12–30 (in Finnish)
Toivonen, J., 1984 Results of stocking with brown trout (Salmo trutta m. lacustris) in Finnish lakes and rivers. EIFAC Tech.Pap., (42)Vol.1:143–51
Tuunainen, P. et al., 1981 Comparative rearing experiments with Baltic salmon (Salmo salar) fingerlings in heated brackish-water effluents and fresh water. In Proceedings of World Symposium on Aquaculture in Heated Effluents and Recirculation Systems, edited by K. Tiews. Stavanger, 28–30 may 1980, (16/17)vol.2:133–44
Westman, K., 1970 Hemoglobin polymorphism and its ontogeny in sea-running and landlocked Atlantic salmon (Salmo salar L.). Ann.Acad.Sci.Fenn.(A)(Biol.), 170:1–28
Westman, K. and P. Tuunainen, 1984 A review of fish and crayfish introductions made in Finland. EIFAC Tech.Pap., (42) Vol.2:436–48
Table 1 Fish stockings in Finland over the years 1978–80 (for further information see Table 3)
|Stockings (1 000 individuals)|
|Newly hatched and feeding juveniles||Juveniles of one growth period in age||Juveniles of at least two growth periods in age|
|Whitefish, vendace||114 233||111 407||174 096||20 557||26 074||27 389||1 153||8||1 033|
|Sea trout, brown trout||2 354||3 095||2 230||180||317||398||1 437||1 738||2 108|
|Landlocked salmon, rainbow trout, char, brook trout, lake trout, grayling||4 604||4 196||1 523||560||623||753||247||142||288|
|Pike, pike-perch, bream, carp, tench||16 778||24 992||18 304||931||2 326||1 836||10||10||6|
Table 2 Production to stockings in 1980 (1 000 individuals)
|Newly hatched4||1 summer old5||1 year old||2 summers old||2 years old||3 summers old||3 years old||older||Total (excluding newly hatched)|
|Coregonus pidschian||5 970||3 109||-||-||-||-||-||-||3 109|
|C. lavaretus||155 470||8 876||-||1 022||-||-||-||-||9 898|
|C. muksun||5 211||7 986||3||6||-||-||-||-||7 995|
|C. peled||675||5 164||936||-||5||-||-||-||6 105|
|Coregonus sp.||5 550||1 315||-||-||-||-||-||-||1 315|
|C. albula||1 220||-||-||-||-||-||-||-||-|
|S. salar m. sebago||180||4||-||36||95||6||1||-||142|
|S. trutta (m. trutta)||509||71||113||153||529||65||11||0||942|
|S. trutta m. lacustris||1 069||169||42||121||903||164||71||1||1 471|
|S. trutta m. fario||652||0||3||-||-||-||-||0||3|
|Esox lucius||17 894||1 722||-||-||-||-||-||-||1 722|
4 Salmonids free-swimming fry
5 Pike fingerlings a few weeks old
Table 3 Details of the principal production methods for fish species raised in Finland
|Principal culture method||General stocking age and size||Rearing spaces and methods during the first (I) and second (II) periods of growth|
|Species||Natural spawning||Intensive brood fish cultivation on farm||Extensive brood fish cult./natural waters||Rearing/natural food ponds||Intensive cultivation||Pond and basin type||Pond size||Initial density|
|Food||Stocking size Production|
|Whitefish||+++||+++||+||x||1s||8–12 cm||nfp||100 m2–200 ha||1–3||natural||0.5–2|
|Salmon||(+)||+++||x||2 y||15–20 cm||ab||ep||1–7 m2||50–500||1500–3000||50–300||dry||50–200|
|Trout||+||+++||x||2 y||18–23 cm||"||"||"||"||"||"||"||"|
|Grayling||+++||x||1 s||8–10 cm||nfp||5–50 ha||1–3||natural||0.3–1|
|Pike||+++||x||<1 s||5–8 cm||nfp||100 m2–10 ha||5–10||natural||1–4|
|Pike-perch||+++||(+)||x||1 s||6–10 cm||nfp||100 m2–15 ha||0.5–3||natural||0.2–1|
nfp natural food pond
ab artificial basin
ep earthen pond
Table 4 Growth of cultivation capacity of Finnish fish farms over the years 1978–80
|Incubation capacity in egg-litres|
|Hatching jars||10 980||(42)||10 910||(52)||10 920||(52)|
|Incubator trays||8 150||(46)||10 270||(47)||10 430||(52)|
|Type of pond|
|Artificial basins||ind.||1 743||(49)||2 213||(73)||2 021||(62)|
|1 000 m2||14||15||21|
|Earthen ponds||ind.||1 424||(118)||1 459||(128)||1 684||(169)|
|1 000 m2||650||686||806|
|Net cages and enclosures||ind.||295||(44)||300||(40)||562||(91)|
|1 000 m2||256||211||255|
|Natural food ponds||ind.||496||(154)||538||(169)||603||(180)|
|ha||3 816||4 636||5 093|
|Fish farms, total||ind.||324||362||422|
N = Number of fish farms involved
Table 5 Fish markings with Carlin tag 1978–81
|Baltic herring||9 119||13 533||2 436||7 323|
|Whitefish||6 269||3 718||6 405||469|
|Atlantic salmon||14 128||18 640||22 448||26 703|
|Landlocked salmon||1 507||2 496||2 989||2 483|
|Sea trout||5 433||21 835||13 220||5 900|
|Brown trout, non-migr.||100|
|Brown trout||7 498||13 826||11 901||13 984|
|Lake trout||1 500||4 981||2 493||1 495|
|Carp||623||1 996||1 096|
|Burbot||1 505||443||1 083||904|
|Perch||3 390||400||1 131|
|TOTAL||58 414||82 219||68 302||64 412|
Fig. 1 The distribution of salmonid fish juvenile production in Finland in 1978. On the left salmonids, on the right coregonids. Production of newly-hatched fish not included.