M. Grande
Norwegian Institute for Water Research
Oslo, Norway
ABSTRACT
The brook trout was first introduced to Norway in 1876. Since then the fish has been stocked in many parts of Norway, but only a few naturalized populations occur. These are found in the upper parts of creeks and small rivers. Stocking experiments have shown that the brook trout may survive and thrive in rather acid waters (pH down to about 4.5) and seems to be more tolerant than the native species and the rainbow trout (Salmo gairdnerii Richardson). Survival tests in acid river water and physiological studies seem to confirm these results.
The brook trout may grow faster than the brown trout (Salmo trutta L.) in acid lakes and obtain a better condition and quality. On the other hand it is a more short-lived species than the brown trout and does not attain the same size. It usually migrates out of lakes in the autumn upon reaching sexual maturity after one to three years. It is advisable to catch most of the brook trout in the second year after stocking due to high natural mortality and migration. The number of the fish stocked therefore must not exceed that at which the fish reach a catchable size within two years.
RESUME
Le saumon de fontaine a éte introduit en Norvège pour la première fois en 1876. Depuis lors, ce poisson a servi à empoissonner de nombreuses régions du pays, mais il ne subsiste que quelques populations acclimatées. On le trouve dans les parties amont des petits cours d'eau. Les expériences d'empoissonnement ont montré que le saumon de fontaine peut survivre et se développer dans des eaux relativement acides (pH descendant jusqu'à environ 4,5) et qu'il semble être plus tolérant que les espèces indigènes et la truite arc-en-ciel (Salmo gairdnerii Richardson). Des tests de survie dans des eaux de rivière acides et des études physiologiques semblent confirmer ces résultats.
Le saumon de fontaine peut grossir plus vite que la truite de rivière (Salmo trutta L.) dans les lacs acides et acquérir une condition et une qualité supérieures. Cependant, il vit moins que cette truite et n'atteint pas la même taille. En général, il quitte les lacs en automne après avoir atteint sa maturité sexuelle en un à trois ans. Il est recommandable de capturer la plupart des saumons de fontaine au cours de la deuxième année suivant le repeuplement, étant donné la haute mortalité naturelle et les migrations. Le nombre des poissons stockés ne doit donc pas dépasser celui des poissons de taille capturable au cours d'une période de deux années.
In Norway there has been only a moderate interest in introducing and stocking exotic fish species. Today a special licence is required to introduce new fish species to waters in which they are not already found. The two salmonids rainbow trout (Salmo gairdnerii) and brook trout (Salvelinus fontinalis), however, have been introduced and stocked more or less intensively for the last 100 years. The interest in brook trout has increased in the last decade due to the fact that it may be an alternative to the native brown trout in acid lakes (Grande et al., 1978). In Norway more than 1 500 lakes and a large number of running waters have lost their fish populations due to acid precipitation (Jensen and Snekvik, 1972; Sevaldrud et al., 1980). Several thousands of native self-reproducing fish stocks have thus been eliminated. It is, therefore, of great importance to find valuable fish species which may be equally or even more tolerant to acid stress as native species. With this background the following presentation on the brook trout in Norway is made.
The first introduction of brook trout to Norway was made in the winter 1876–77. Eggs were imported directly from North America. The larvae of these eggs were stocked in some localities around Oslo, but only a few fishes were recaptured and no reproduction occurred (Collett, 1905).
In 1883 a new batch of eggs was imported from North America and in the following years (to 1890) fry of brook trout were stocked several places in Norway. In most places stocking apparently did not succeed but there were also reports of recaptures of fish up to a size of 1.5 kg. In 1909–10 there was a new series of stockings in central Norway of fish originating from the introduction in 1883 (Landmark, 1894, 1910). From all these stockings probably only one self-reproducing stock was established in a small river, and this did not become officially known until 1969. It is still not known exactly when stocking of this population took place.
In 1918 about 1 000 fry of brook trout were imported from Denmark and stocked into a lake in Oyfjell in Norway. This resulted in self-reproducing stocks in several small brooks and rivers (Huitfeldt-Kaas, 1924; Huitfeldt, 1947 and Grande, 1964).
In the years 1966–69 some stocking experiments with brook trout of the Oyfjell (Norway) population and other salmonids in acid lakes indicated that brook trout was relatively tolerant to acid water (Grande et al., 1978). This led to increased interest in this fish and in the seventies the fish was stocked extensively in Norway, especially in areas where acid precipitation has led to fish mortalities. Some of these recent stockings have led to naturalized populations, probably only in creeks and small rivers.
As mentioned in the previous chapter a few naturalized populations of brook trout have become established in creeks and small rivers. Some comments shall be given to these populations and especially those in the Oyfjell area in Telemark which was investigated in 1958–60 (Grande, 1964).
The population in Oyfjell was in 1960 the only officially known population of brook trout in Norway. It was studied with regard to distribution, population size, age and growth, reproduction and feeding habits. A comparison with the brown trout (Salmo trutta L.) in the same water system was also made.
3.1.1. Distribution
It was found that the brook trout was distributed in five oligotrophic creeks and rivers (pH 5.8–6.5, conductivity 13–25 uS/cm at 20°C) about 600–1 000 m above sea level. In the upper parts of the water system it was found alone; there was also an area where it coexisted with the brown trout. Further downstream the brown trout was alone and brook trout occurred only sporadically. The mean annual water flow was 40–280 1/s in the localities where brook trout were dominant (Fig. 1).
3.1.2 Population size
The brook trout were small, and most of the fish caught weighed 30–80 g. The brown trout caught in the same localities usually reached a higher maximum size. By means of a marking technique the population in two creeks with brook trout was estimated to 650 and 800 g/100 m2, respectively.
3.1.3 Age and growth
Examination of otoliths and scales indicated that the oldest brook trout sampled were eight winters old. However, few fish in the catches were older than 2–4 years. The brown trout caught were generally older than the brook trout. The growth rate of the brook trout was calculated to be about 6.0, 4.5, 4.0 and 3.0 cm, respectively, in the first four years of life. From the fourth year of life stagnation of growth was remarkable. The brook trout seemed to grow somewhat faster than the brown trout in the first year of life, but after this the growth rate was about the same for the two species.
3.1.4 Sexual maturity and spawning
Sexual maturity occurred after one winter for fast-growing males of brook trout. Usually the first spawning took place after two to three winters for the males and after three winters for the females. The brown trout reached maturity later than the brook trout, and the first spawning usually seemed to take place after three to four winters for the males and after three to five winters for the females.
3.1.5 Feeding habits
The brook trout as well as the brown trout lived mainly on insects and there was a marked competition for food between the two species.
3.1.6 Competition
It was concluded from the Oyfjell investigation that the brook trout was able to compete and maintain its numbers in creeks and small rivers in the area.
Further investigations in other localities where brook trout is present have shown that the picture from Oyfjell is typical. In Overnbekken in Buskerud, for example, the brook trout has maintained its numbers in the upper part of a small river for approximately 80 years. Also here it is found alone in the upper part while there is a short stretch where it is found together with the brown trout. Further down the brown trout and also other species completely dominate and brook trout are caught only sporadically.
In the years 1962–76 brook trout fry was stocked by the author in three fishless oligotrophic creeks (200–600 m above sea level). In all cases the brook trout grew up, reproduced and established itself as self-reproducing, naturalized populations. Remarkable in these cases is the stationary tendency of the fish. There is little migration down the creeks from the place where they are stocked, and the fish is practically unknown in the lower part of the water system. Length distribution of fish in catches from two creeks are shown in Fig. 2.
This typical distribution of naturalized brook trout populations in Norway seems to be in concordance with the occurrence of brook trout in Denmark (Ernst and Nielse, 1981), Sweden (Kjellberg, 1969) and other countries in Europe (MacCrimmon et al., 1969 and 1971).
Since 1966 different strains of brook trout, brown trout, rainbow trout and hybrids between brook trout and Arctic charr (Salvelinus alpinus L.) have been stocked in an experimental area with 11 small acid lakes (0.5–25 ha). The Langtjern area is situated in central Norway about 500–600 m above sea level.
The lakes have a pH varying from 4.7–5.5 and a chemistry rather similar to that for Langtjern (Table 1). Most of the lakes have no natural fish populations partly due to lack of spawning areas and party due to the low pH. One example from these stockings is illustrated in Fig. 3. The following conclusions can be made of the results obtained hitherto.
4.1.1 Recaptures
When brook trout, brown trout and rainbow trout were stocked together the recapture of brook trout was generally higher than for brown trout. There were few or no recaptures of rainbow trout. Stocking of the hybrids between brook trout and Arctic char sometimes gave good results. There was relatively little difference between strains of brook trout (Danish domestic, Oyfjell and Temiscamie strain).
There are indications that stocking of brown trout alone gives better results than when it is stocked together with brook trout (Fig. 4).
4.1.2 Age
Most brook trout were caught after 1–3 years of life with a peak in the second year. Very few, if any, caught are older than three years (3+). The brown trout grows older and may be six years or older in the same lake (Fig. 4).
4.1.3 Growth, condition and quality
Under similar conditions brook trout may grow much faster than brown trout, but brown trout may grow larger due to a greater age. Some typical growth rates are shown in Fig. 5. Usually brook trout have good condition, red colour in the flesh and delicious taste even in rather acid lakes with low pH and a high content of humic matter. Its quality in such lakes often seems to be better than the brown trout.
4.1.4 Migrations
The brook trout has a great tendency to migrate downstream out of a lake after 1–2 years of life (Fig. 6). This may, to a great extent, be due to sexual maturity and be regarded as spawning migrations. The tendency to migrate seemed in this case to be much less for the brown trout even if it were sexually mature.
4.1.5 Feeding habits
The brook trout and brown trout have the same mainly insectivorous diet. Corixidae, Chaeborus sp., Sialis spp., Ephemeroptera, Trichoptera and Coleoptera and Odonata are the most important groups. As would be expected, there is competition for food between the two species in the lakes.
These results showed that the brook trout may be regarded as an alternative or supplement to the brown trout in acid lakes. By contrast, the rainbow trout has been a complete failure for stocking into such lakes. It was, therefore, decided to do some experimental stockings of brook trout in lakes in the southern part of Norway which are seriously altered by acid precipitation. In 1975 17 400 fingerlings (0+) of brook trout were stocked in 13 small and medium sized acid lakes in southern Norway. The purpose was to study how this species would thrive in these lakes where stockings of the native brown trout in the last years had failed. Through the period 1975–79 experimental net fishing and water sampling were made in the lakes. The following summarizes the results (Grande et al., 1980).
Stocking was carried out in lakes where the mean pH varied between 4.48–4.98. In three of the lakes stocking resulted in few or no recaptures. Mean pH for these lakes were 4.48, 4.68 and 4.84. Acceptable results were obtained in the other lakes where the most acid had a pH of 4.58. The results are discussed with respect to the water quality in the lakes, and it is concluded that other factors as well as low pH may explain the results.
In the other lakes the mean weight of brook trout for the years 1976 (1+) and 1977 (2+) was 171 and 312 g, respectively. The condition and quality of the fish was good or very good. The stomach content consisted mainly of insects with Corixidae, Chaeborus spp., Sialis spp., Ephemeroptera and Trichoptera as the most important groups.
Nearly all recaptures were made in 1976 and 1977. A great number of the fish migrated out of the lakes. Brook trout were also caught in 1978 and 1979 in those places where recaptures were registered further down the water system. The migration is probably mainly related to the development of sexual maturity after one or two years.
The mean yield in the lakes was 0.9 kg/ha. This is, however, only a minimum number because some recaptures have not been registered.
The increased availability of stocking material has also led to stocking in other biotopes. Per Aass (pers. comm.) has experimented with stocking of marked fish (1+ and 2+) in sea water of the inner Oslo fjord. Typical for these stockings is that brook trout migrate rather rapidly up nearby rivers and creeks where recaptures are made. It is remarkable that some of these rivers are very polluted and have no self-reproducing fish populations. This brook trout originates from the Oyfjell strain mentioned earlier in this article and is an inland, river-dwelling form.
The results from these stockings have led to increased stocking activity of brook trout in acidified areas of Norway. Introduction of exotic species to a water system is forbidden in Norway, but allowances have been made in many cases. Few of these stocking were followed up by investigations, but the general impression from scattered information is as follows. Typical problems are the short life and mass migrations out of the lakes and down the water system. On the other hand, positive aspects are better survival than for the earlier stockings of brown trout and thus a higher recapture rate; also the fish caught are of good quality. There are reports of good results from lakes in which pH at least periodically goes down to 4.3–4.5
In the last ten years brook trout has been stocked in oligotrophic lakes (pH 5.5–6.5) in the surroundings of Oslo together with brown trout and rainbow trout. The stockings have resulted in high numbers of recaptures but many of the fish are caught before they reach an acceptable size. This is also the case with the rainbow trout. These species are more easily caught than the brown trout in the first year of life. To get an optimal catch fishing for brook trout ought to be highest in the second summer after stocking in such lakes as well as in acid lakes (Qvenild and Holt, 1981).
The results obtained in the stocking experiments indicated differences in tolerance to acid water between the salmonids involved. Therefore some experiments were made to study the tolerance of several salmonids to waters with low pH (Grande et al., 1978). One experiment was carried out at a field station in southern Norway. Under-yearlings (0+) of Atlantic salmon (Salmo salar L.), rainbow trout and brook trout were placed in tanks with throughflow of untreated and limed water (temperature 1–4°C) from a nearby acid brook. Twenty-five fish of each species were used. The survival of the fish was then inspected daily during a six-week period.
Results of this experiment are shown in Fig. 7. Table 2 gives the concentrations of some chemical components in the brook water.
The variation in pH of untreated and limed water is illustrated in Fig. 7. This experiment indicates that the tolerance of fish to the stream water can be ranked in the order rainbow trout, Atlantic salmon, brown trout and brook trout, with the latter as the most tolerant. Treatment of water with lime to pH 5.4–6.3 exerted a significantly positive effect on the survival time, but there was still complete mortality among rainbow trout and Atlantic salmon. Recent findings suggest that this may be due to incompletely precipitated aluminium on the gills of the fish (Muniz et al., 1980).
Rosseland (1980) studied the effects of acid water on metabolism and gill ventilation in brown trout and brook trout and found differences in metabolic response in the two species. These differences indicated that the brook trout was more tolerant than brown trout to acid water. Several of his experiments were made at the same field station mentioned above.
Practical experience and experiments in Norway (Jensen and Snekvik, 1972) have shown that the Atlantic salmon is more sensitive to acid water than brown trout. On the basis of Swedish experience Berzins (1960) maintains that the thresholds for mortality are pH 5.5, 5.0 and 4.8 for rainbow trout, brown trout and brook trout, respectively. Trojnar (1977) concludes from studying the results of Daye and Garside (1975) and Johnson (1975) on brook trout and Lloyd and Jordan (1964) and Kwain (1975) on rainbow trout that brook trout are clearly more tolerant than rainbow trout. Investigations of the distribution of fish in hydrogen-ion gradients in a creek indicated that brook trout was more tolerant than brown trout (Dunson and Martin, 1973).
Power (1980) has given a thorough discussion of some abiotic factors controlling the distribution of brook trout, among them the hydrogen-ion concentration. From this it can also be concluded that brook trout are more tolerant to acid water than the rainbow trout. However, more research on the relative tolerance of different species and strains of salmonids to acid waters is evidently needed.
Some practical conclusions from the results obtained hitherto follow. These conclusions and tentative guidelines for management apply to Norwegian conditions and may not, of course, be valid under other circumstances (Grande et al., 1980).
Evidently the brook trout has difficulty in reproducing and establishing itself in larger water bodies in Norway. If brown trout are able to thrive, it will usually displace brook trout. Similar results have been obtained from other countries in Europe and from U.S.A. where the brown trout has been introduced from Europe. Self-reproducing populations of brook trout will probably only be established in small rivers with a good water quality. In some of these localities it may be able to displace the brown trout. It is not known how it will be able to compete in elevated mountain lakes.
Brook trout in Norway usually spawn in running water in autumn, at the same time as brown trout. The eggs are hatched in spring. The fry and large fish seem to have approximately the same food habits as brown trout with preference for insects, crustaceans and mussels. The fish are usually short-lived (3–5 years) but can grow older under special circumstances. They are sexually mature after one-three years, the males usually one year before the females. Brook trout may reach a weight of up to 1 000 g or even larger under favourable conditions. In Norway good growth after stocking in acid lakes has been 300–600–900 g after one, two and three years, respectively.
Experience in Norway has shown that stocking of under-yearlings (0+) of brook trout and older fish may give good results in acid lakes. In some cases the fish may live well in lakes with pH values of about 4.6–4.7 and even lower (down to 4.3–4.5) if the other physical/chemical conditions are good (e.g., rich in humic matter, no oxygen deficiency in late winter). Good results imply that the fish survive and have good growth and that stocking gives good recaptures by the common fishing procedures. Reproduction will usually not occur in localities with pH below about 5.0.
Growth depends, among other things, on the number of fish stocked in relation to the productivity of the water. If the lake has been fishless for some years, it may have accumulated a considerable amount of food and growth may be good. During continuous stocking growth may be poorer due to reduced quantity of available food items. This ought to be taken into consideration, and the number of fish regulated accordingly. About 20–50 fish (0+) per hectare has proved to give good results in many occasions by the first stocking.
Experience indicates that it might be preferable to stock brook trout in a greater number every three or four years instead of each year - the usual practice for the brown trout. In this way it is easier to control the population by fishing the right year classes and to protect the newly stocked fish from being eaten by larger fish. It should then also be possible to re-establish the population of food organisms if the lake is more or less empty of fish for one summer. It is possibly important that there is a good supply of food in the stocking period so that the fish will have a better chance to withstand stress due to changes in water quality (low pH-aluminium).
If possible, it might be preferable to stock the fish in the summer, when the water temperature is higher, and when the water quality often is best and the population of small food animals (e.g., crustaceans) is high.
Since the brook trout was first introduced into Norway in 1876 the fish has not created any problems in Norwegian waters. This seems to be the case also in other countries in Europe. There does not seem to be any risk in stocking brook trout in forest areas in southern Norway. Here, it should primarily be stocked in fishless or nearly fishless lakes where the brown trout does not thrive due to high acidity. It might be best suited to relatively high-elevation lakes (300–700 m above sea level). In high mountain lakes and the northern part of Norway uncontrolled stockings should await further experiments. This is because the fish may spawn directly in the lake which becomes overpopulated as has occurred in some parts of U.S.A. (Moyle, 1976).
The brook trout has a great tendency to migrate out of the lake one to three years after stocking. It is also a short-lived species. The number of fish stocked therefore must not exceed that at which the fish reach a catchable size (at least 100–200 g) after one year. Closing of the outlet of the lake by a net or similar arrangement may reduce migration. In Norway, however, this requires a special licence.
Migration is usually downstream. If the circumstances are suitable, considerable recaptures might be possible in those areas. This may be taken into consideration in stocking programmes in which the whole water system may be looked upon as a unit.
The brook trout is less shy than the brown trout and is easier to catch in nets as well as on lines. This means that the fish can be caught with less effort, but might also be wrongly harvested. If there is intense and uncontrolled fishery (near urban areas, e.g., Oslo) there will often be overfishing of small and unvaluable fish the first year and the efficiency of stocking is rather doubtful. It is advisable to catch most of the brook trout in the second year after stocking due to high natural mortality and migration.
The brook trout has proved to have many valuable properties relative to the brown trout and warrants more attention in the future. More research is needed, and it is important to obtain more knowledge about its ecology and the practical advantages and disadvantages in relation to other salmonids in Norwegian water types. Management of the brook trout in acid lakes should be studied more intensively. It is also of interest to carry out more experiments with hybrids of brook trout and other species such as the Arctic charr and lake trout (Salvelinus namaycush).
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Table 1 Chemical data, Langtjern. Samples collected at 1 m depth over the period 23 January 1974 to 10 Octobrer 1976. (From Henriksen and Wright, 1977)
| Components | No. of observations | Mean | Standard deviation |
| pH | 90 | 4.95 | 0.23 |
Conductivity uS/cm 20°C | 90 | 17.70 | 3.10 |
| Colour mg Pt/l | 86 | 100.00 | 30.00 |
| Ca mg/l | 88 | 1.38 | 0.27 |
| Mg mg/l | 89 | 0.76 | 0.04 |
| Na mg/l | 74 | 0.70 | 0.18 |
| Cl mg/l | 86 | 0.68 | 0.16 |
| Al ug/l | 73 | 218.00 | 46.00 |
Table 2 Physical and chemical data from Ramse Brook, Tovdal. Samples collected in experimental period 19 December 1973 to 31 January 1974 (Grande et al., 1978)
| Components | Mean | Range |
| pH | 4.57 | 4.40–4.60 |
Conductivity uS/cm 20°C | 23.10 | 11.50–37.70 |
| Colour mg Pt/l | 9.70 | 0 –19.50 |
| Ca mg/l | 0.85 | 0.73–0.97 |
| Mg mg/l | 0.36 | 0.31–0.41 |
| K mg/l | 0.08 | 0.04–0.12 |
| Cl mg/l | 2.00 | 1.60–2.60 |
| SO4mg/l | 6.90 | 5.00–8.90 |
| Temp. °C | 2.50 | 1.00–4.00 |
Fig. 1 Distribution of brook charr in the Øyfjell area (Grande, 1964). The brook charr occupies the upper parts of the water system, while it is found together with brown trout in a medium zone. In the lower parts the brown trout dominates completely, and brook charr is only found sporadically.
Fig. 2 Typical length distribution of naturalized brook charr sampled by electro-fishing in two small rivers in late autumn. The low number of 0+ year-class is due to selectivity of the fishing method.
Fig. 3 Recaptures from stocking of brook charr, brown trout and rainbow trout (0+) in an acid lake, Langtjern. pH in outlet (Grande et al., 1978)
Fig. 4 Recaptures of brown trout and “Temiscamie” and “Øyfjell” strain of brook charr from Langtjern when brown trout was stocked alone (1975) and the two brook charr strains together (1977). Total recaptures brown trout: 30.3%, Temiscamie strain 32.6%, Øyfjell strain 27.6%. (The Temiscamie strain comes from the southeast James Bay area, Quebec and was provided in 1977 by Dwight A. Webster and Carl Schofield, Adirondach Fishery Research Program of Cornell University, U.S.A.)
Fig. 5 Growth of brook charr stocked in some acid lakes in southern Norway 1975 (Grande et al., 1980)
Fig. 6 Recaptures in outlet-trap of Langtjern. Migration of brook charr usually occurs the second or third autumn after stockings of 0+ (Grande et al., 1978)
Fig. 7 Mortality of salmonids (0+) in tanks supplied with acid stream water (Grande et al., 1978)
