THE ENHANCEMENT OF EEL STOCKS IN FINLAND; A REVIEW OF INTRODUCTION AND STOCKINGS

M. Pursiainen
Evo Inland Fisheries and Aquaculture Research Station
Evo, Finland

and

J. Toivonen
Finnish Game and Fisheries Research Institute
Helsinki, Finland

ABSTRACT

Eel populations in Finnish fresh waters have never been dense because of Finland's northern location. Young eels, which in the past migrated up rivers to lakes, are nowadays unable to reach the lakes because most rivers are blocked by dams. Therefore, stocking represents the only possibility for maintaining eel populations in inland waters.

Stocking experiments began on a small scale as early as 1894. During the last 20 years, stocking has been carried out to some degree almost every year. In general, small yellow eels have been used as stocking material; glass eels (elvers) have been stocked only a few times. Most of the stocking has been done in southern Finland.

Stockings have generally been successful: in particular, the results of the relatively large introductions of glass eels (elvers) in the sixties are clearly visible in Finnish catch statistics. The eel catch in inland waters has grown from 9 t in 1976 to 63 t in 1980. In some registered cases, fishermen have caught almost 30 percent of stocked eels with ordinary fishing methods. A survival rate of over 70 percent within nine years following introduction has been recorded using rotenone sampling.

The main difficulties in eel stocking in Finland are the cold weather in March–April during the elver stocking period and the possibility of elvers being carriers of viral fish diseases. Therefore, it has been considered that the stockings should be made with reared fingerlings which can be released during the summer after careful disease control.

RESUME

Les populations d'anguilles n'ont jamais été très denses dans les eaux douces de Finlande, ce qui tient à la position septentrionnale de ce pays. Les jeunes anguillcs qui, autrefois, remontaient les fleuves pour s'installer dans les lacs en sont aujourd'hui empêchées par les barrages que l'on a édifiés sur la plupart des cours d'eau. Le repeuplement est donc le seul moyen de conserver des populations d'anguilles dans les eaux intérieures.

Les premières expériences de repeuplement ont été effectuées, sur une échelle modeste, en 1894. Depuis vingt ans, on repeuple les eaux presque chaque année en employant en général de petites anguilles jaunes. Les civelles transparentes ont rarement été utilisées. On repeuple essentiellement les eaux du sud de la Finlande.

Les opérations de repeuplement ont en général, été couronnées de succès; les statistiques montrent en particulier que les captures se sont nettement améliorées à la suite des introductions relativement importantes de civelles transparentes au cours des années soixante. Les captures d'anguilles dans les eaux intérieures sont passées de 9 t en 1976 à 63 t en 1980. Dans certains cas, les pêcheurs ont capturé, avec des méthodes ordinaires de pêche, près de 30 pour cent des anguilles de repeuplement. Grâce à l'utilisation du roténone, on a réussi à obtenir un taux de survie supérieur à 70 pour cent neuf ans après l'introduction.

Le repeuplement en anguilles des eaux finlandaises se heurte essentiellement à deux problèmes. D'une part, le temps est encore très froid en mars-avril lorsque l'on met à l'eau les civelles et, d'autre part, celles-ci risquent d'être porteuses de virus transmissibles aux autres poissons. Il faudrait donc utiliser des alevins d'élevage qui pourraient être mis à l'eau durant l'été après un examen sanitaire soigneux.

1. INTRODUCTION

Eel populations in Finnish fresh waters have probably never been dense, because of Finland's northerly geographical location and distance from the Atlantic. Young eels have, however, migrated upriver to inland waters previous to the commencement of river damming operations for electric power plants. For instance, some examples of upstream migrating eels have been caught by lamprey fishing. The eels were all females and, as is usual in Finland, were rather large (27–54 cm long) (Nordqvist, 1903; Jarvi, 1909 and 1936).

For these reasons, eel fishing has been of only slight significance in Finland. Nevertheless, in some areas fishing for silver eel took place in rivers and on the Baltic coast (Jarvi, 1932) but this ceased almost entirely after the main rivers were closed in the thirties. The first eel stockings were made as early as 1894 in an attempt to improve eel fishing possibilities (Brofeldt, 1920). Eel introductions and stockings have, however, been rather sporadic and not until the sixties was greater attention given to this practice (Toivonen, 1966).

This report deals with eel introductions and stockings from the year 1960, some individual results from earlier years and especially discusses the present freshwater eel fishery, which is almost totally dependent on stocking.

2. STOCKING

2.1 Origin of the material

The number of eels reaching the Baltic coast of Finland is so small that it is unprofitable to acquire stocking material from the river mouths. Therefore, young yellow eels have been introduced from Denmark, as well as from Germany and in smaller amounts from Sweden. During the last two decades the material for introductions has come mainly from Denmark but these introductions have now ceased because the export of small, under-sized eels from Denmark is forbidden. Glass eels and/or elvers have been introduced three times in the sixties and once in the seventies (see also Table 1).

Small yellow eels for introduction were transported by tank trucks and elvers in moist boxes by air.

2.2 Amounts stocked

The eel stockings carried out in Finland during 1960–79 have been listed in Table 1. This shows that stockings were actively carried out in the sixties, with a mean yearly stocking of 830 000 specimens, of which 781 000 (94 percent) were elvers and 48 500 small yellow eels. During the seventies, the stocking rate dropped to only 57 200 specimens per year, of which 36 800 (64 percent) were elvers and 20 400 yellow eels. The main reason for this decreasing was the risk of transporting communicable fish diseases together with the stocking material.

Stocking material was distributed among the statistical areas used by the Finnish Game and Fisheries Research Institute, as shown in Fig. 1. Most stockings were directed to southern Finland's small inland waters (Area 1) and to the area called Lake Finland (Areas 2, 3 and 4). Stockings of small yellow eels have clearly been concentrated in southern Finland (Areas 1 and 4, see Fig. 1).

The mean size of elvers introduced to Finland has been about 0.3 g, while that of small yellow eels has varied from 3.5 to 56.2 g (see also Table 1). During the sixties it was still possible to obtain very small yellow eels with a mean weight of 8.4 g for introduction but during the seventies the mean weight rose to 44.5 g.

The value of the stocking material in the sixties can be calculated using current eighties prices at 820 000 Finnish marks (FIM), which corresponds to about U.S.$ 200 000. During the seventies this value was about 300 000 FIM (U.S.$ 70 000).

3. RESULTS OF INTRODUCTIONS AND STOCKINGS

Results of stocking in Finland can be examined both on the basis of some individual cases and also by comparing the stockings made in the sixties with the catch in the second half of the seventies.

3.1 Individual cases

Yellow eel stockings in some small forest lakes at the Evo Inland Fisheries and Aquaculture Research Station (61°10'N) in the beginning of this century have given the results shown in Table 2. Fishing for eels in these lakes has been irregular and done using ordinary fishing methods; but because the lakes have no outlets, the calculated survival rates can be considered as relatively reliable. The mean survival rate has been 27.4 percent of stocked eels, and the size of caught specimens about 1 kg (Brofeldt, 1955). This is the equivalent of a catch of approximately 200 kg/1 000 stocked specimens.

Table 2 also shows the results from two lakes in northern Finland near Rovaniemi (66°30'N), which were stocked in 1954 and treated with rotenone in 1963 and 1964 (Toivonen, 1966). In the smaller lake (Pohtimolampi) the stocking rate has probably been too large, taking into consideration the surface area and northern location of the lake, and the very small mean weight of caught specimens, only 60 g. The survival rate in this case has, however, been exceptionally high: 72 percent of stocked eels within nine years. Because of poor growth, the catch in this lake was only 43 kg/1 000 stocked specimens. In the other lake (Pasmajarvi), some of the eels may have escaped for their spawning migration, because in sampling the catch with rotenone only 20 percent of the eels stocked were recovered; the mean weight of specimens caught was 600 g. However, the catch was nonetheless about 120 kg/1 000 stocked specimens.

The results presented here clearly show that the survival rate of young yellow eels is very high, and stockings are therefore rather profitable. For elver stockings such individual results cannot be presented, because the first stockings of this kind were made in the second half of the sixties and all the eels from such stockings have not yet been fished out.

3.2 Catch statistics

Eel has been considered as a separate species only since 1976 in the Finnish Game and Fisheries Research Institute's official fisheries statistics (see Table 3). These statistics can be considered reliable from the year 1977 onward, as the results of non-professional fishermen were used as a basis for assessment from 1975 (Lehtonen and Salojarvi, 1978). The total catch of eel in the marine fishery has been steady but inland catches have grown slightly since 1977.

The catch of eel from inland waters is based almost totally on stocking. From ageing studies it appears that catches made in the second half of the seventies are derived from stockings made in the sixties. Since at that time the yearly amount stocked was about 830 000 specimens, it can be estimated that they have produced a catch of circa 60 t/year in the second half of the seventies. This is equivalent to a catch of approximately 72 kg/1 000 stocked specimens. In Finland fishing and marketing of eel are not effectively organized and, for example, there is almost no fishery for silver eel in rivers. Furthermore, according to catch statistics over 96 percent of the total catch is caught by non-professional fishermen. These estimates are therefore likely to be low.

The best picture of the relationship between stockings and catch can be obtained by examining stockings and eel catches in various statistical areas. The greater part of the eel catch is taken by non-professional fishermen and in 1975 the eel catch was 45 t (Lehtonen and Salojarvi, 1978) and 66 t in 1978 (Lehtonen and Salojarvi, unpublished data). The mean yearly catch divided according to various statistical areas is shown in Fig. 2. The figure clearly shows how stockings (see Fig. 1) in the sixties are mirrored in catches in the second half of the seventies. For example, southern Finland's small inland waters (Area 1) received 18 percent of all eel stockings in the sixties, and the eel catch has been about 24 percent of the yearly total catch of eels. In some areas, eel fishing is rather low compared to the amounts stocked; for example, Area 2 (eastern Finland) received 18 percent of all eels stocked in the sixties, but the eel catch here has been only 9 percent of the annual total. The most important stocking area (4) received 43 percent of the elvers and young yellow eels stocked in the sixties and this is reflected in the area's large share (49 percent) of the whole country's eel catch.

3.3 The profitability of stockings

The result of eel stockings in the sixties was a catch of about 72 kg/1 000 stocked specimens and in some individual cases even over 200 kg. A comparison between the different areas shows the best result to have been obtained in Area 1 (southern Finland), where the catch reached about 90 kg/1 000 stocked specimens. This compares with about 76 kg in Area 4 and only a little over 10 kg/1 000 specimens in northern Finland (Areas 6 and 7). Of course, the size of the catch depends greatly on the intensity of fishing, which is low for eels in those areas where the eel is rather unknown.

It is difficult to come to any conclusions as to differences in the results between stockings of elvers and those of young yellow eels. In Areas 1 and 4, stockings with yellow eels accounted for a relatively great proportion of all stockings (see Fig. 1), which may to some extent also be reflected in the catches. Eel fishing has a long history in these areas and, therefore, catches are relatively better than in other areas. In central Finland (Area 3) stocking with yellow eels has been almost insignificant, but the percentage ratio of catch to stocking is almost the same as in Areas 1 and 4. Therefore, it seems that elver stockings in 1966–68 produced the most important part of the whole country's present eel catch.

By comparing the expenses incurred in stocking with the value of the catch, it is possible to make estimates of the economic profitability of stocking. In the sixties the cost of stocking was about 820 000 FIM, i.e., 82 000 FIM per year, calculated according to 1980 prices. The value of the present yearly eel catch in inland waters is about 600 000 FIM, i.e., about seven times annual stocking expenses. If inflation is taken into account in a comparison with the real stocking expenses incurred in the sixties (Toivonen, 1966), the value of the present catch is more than 50 times that of expenses.

4. PRESENT AND FUTURE ACTIVITIES

Stocking with elvers presents certain difficulties in Finland. Firstly, at the time of year when elvers can be introduced, i.e., in March–April, the lakes are still very cold and under ice cover. Secondly, and more important, is the possibility that elvers can be carriers of viral fish diseases which creates a certain risk, because Finland is, as far as is known, free of such diseases.

Small, under-sized yellow eels can no longer be introduced, due to new legislation by the exporting countries. This type of stocking is also rather expensive, although it still might be economically profitable.

No special negative effects of eel stockings have been found and therefore these activities should be continued. Because of the difficulties mentioned above, it is considered that stockings should be made with reared fingerling eels which can be released into waters during the summer, after a few months of careful control for diseases especially those arising from viruses.

5. REFERENCES

Brofeldt, P., 1920 Evon kalastuskoeasema. 25-vuotinen toiminta ja tulokset 1892–1917. Suom.Kalatal., 6:1–141

Brofeldt, P., 1955 Ankeriaasta ja sen istuttamisesta vesistoihimme. Suom.Kalastusyhdistys Opaskirja, 24:1–19

Jarvi, T.H., 1909 Beobachtungen uber die Grosse und das alter der Aale in Binnengewassern Finnlands. Medd.Soc.Fauna Flora Fenn., 35:218–21

Jarvi, T.H., 1932 Suomen merikalastus ja jokipyynti. Porvoo, Finland, WSOY, 188 p.

Jarvi, T.H., 1936 Saapuneita ja lahteneita ankeriaits. Hajanaisia havaintoja. 10. Eripainos Suom.Kalastuslehti, 1936:26–34

Lehtonen, H. and K. Salojarvi, 1978 Kotitarve- ja virkistyskalastus Suomessa vuonna 1975. Suom.Kalatal., 48:41–55

Nordqvist, O., 1903 Some observations about eel in Finland. Medd.Soc.Fauna Flora Fenn., 29:48–54

Toivonen, J., 1966 Ankeriaan istuttamisen nakymista. Suom.Kalastuslehti, 73:148–54

Table 1 Eel stocking in Finland in 1960–79

* The origin of the material
(Denmark = D;
France = F;
Germany = G;
Sweden = S)

Table 2 Eel stockings and their results in some small forest lakes in southern Finland (61°10'N) (Brofelt, 1920 and 1955) and two results from northern Finland (66°30'N) (Toivonen, 1966)

Table 3 Finland's eel fishing statistics from 1976 to 1980 Statistics from the year 1976 are unreliable Catches given in 1 000 kg

Fig. 1 Eel stockings in Finland in 1960–69 (left columns) and in 1970–79 (right columns) in various statistical areas. Shaded parts represent yellow eel stockings and light parts elver stockings

Fig. 2 Mean eel catches in the second half of the seventies in various statistical areas