Finland, Norway and Sweden have in total about 126500 lakes larger than four hectares. In Finland and Sweden, approximately 10% of the surface area is freshwater; whereas in Norway, it is about 6%. Altogether 56 fish species are reproducing in the Nordic freshwaters, including four lamprey species. Due to geographical differences, the freshwater fish fauna differs considerably in the northern and southern parts; but species richness increases also from west to east. The proportion of recreational fishermen in Norway, Finland and Sweden was about 50%, 40% and 27 %, respectively, in 2004. Professional freshwater fishing is declining, but is still important in some lakes in Finland and Sweden. In all three countries, fishing rights belong to the water or land owner, with some exceptions.

Water quality has improved in recent decades due to decreased nutrient loads from point sources, but the limitation of scattered nutrient loads has been less successful. This development can also be seen in the responses of fish communities. Some 30–40 years ago, waters close to many cities or industrial plants were heavily polluted and had only limited recreational or fisheries value. Recently, they are often inhabited by healthy fish populations. On the other hand, there are many highly eutrophic lakes in agricultural areas of southern and western Finland and Sweden that regularly suffer from algal blooms and high biomasses of cyprinid fish. The increasing acidification problem of oligotrophic lakes was related to long distance air pollution in recent years, but the situation has now improved. Lake regulation impacts the littoral ecosystems in hundreds of lakes and causes considerable negative impacts on feeding and reproduction areas for fish. The main measure used for compensating the damaged fish numbers has been stocking. Many large rivers have been modified for hydropower production. Most activities of fish habitat restoration are directed at rivers. Fisheries management includes several tools: regulations on use and structure of fishing gear, temporal and regional fishing restrictions, the size limits of target fish, the limitations of fishing efficiency, and amount of catch. The general goal is to meet the principles of sustainable use of natural resources.

Introduction

Finland, Norway and Sweden are situated in northwestern Europe (Figure 1) and all three countries have numerous lakes and rivers. In addition, the Baltic Sea has brackish water and its fish fauna consists of both freshwater and marine species. Both fresh waters and the Baltic Sea came into being when the continental ice sheet melted about 10000 years ago. Humans came to the Nordic lake shores when the ice retreated, partly due to abundant fish stocks. Today, there are about 20 million people living in these three Nordic countries. Fishing is one of the most important outdoor activities and the share of recreational fishermen is bigger than in any other part of Europe (Toivonen et al., 2000).

Figure 1.

Geographical location of Finland, Norway and Sweden in Europe.

Figure 1.

Geographical location of Finland, Norway and Sweden in Europe.

The purpose of this paper is to give a regional overview of Nordic freshwater resources, its freshwater fish fauna and fisheries, the current status of freshwater habitats, and freshwater fish management including the legislative and regulatory treatment of fish, habitat, and fisheries and the impacts of environmental changes.

The history of fresh waters and their fish fauna in the Nordic countries

The Nordic freshwater fish communities started to form some 10000 years ago when the last glaciation period terminated. The ancestors of present fishes lived in refuges outside the ice sheet. Melting ice formed the huge Baltic Ice Lake which extended from northern to central Europe. Present lakes and rivers were separated from the main basin by land uplift. The landscape has been formed by the nature of the bedrock and by the withdrawing ice at the end of the last ice age. The ice sheet covered the whole northern Europe and the natural lakes in northern Europe are of glacial origin.

The first immigrating freshwater fish were cold water species, such as fourhorned sculpin (Triglopsis quadricornis), brown trout (Salmo trutta), salmon (Salmo salar), whitefish (Coregonus lavaretus), Arctic charr (Salvelinus alpinus), smelt (Osmerus eperlanus) and burbot (Lota lota). All these species were adapted to live in good oxygen conditions and reproduce at low temperatures. At the next juncture came vendace (Coregonus albula), grayling (Thymallus thymallus), three-spined stickleback (Gasterosteus aculeatus), alpine bullhead (Cottus poecilopus), perch (Perca fluviatilis), pike (Esox lucius) and minnow (Phoxinus phoxinus).

Since the first immigrants, the number of freshwater fish has been constantly increasing in the Nordic countries. However, the low salinity of the Baltic Sea together with the relatively cold climate formed an effective migration barrier and prevented many species from moving northward.

During the last centuries, human activities have strongly affected freshwater fish communities. Introduction of exotic species and forms, degradation of water quality, fishing and physical changes, such as draining and regulation of lake levels and flood protection, as well as damming of rivers for the production of hydroelectric power have had enormous effects. The degree and type of anthropogenic influence varies in the different parts of three Nordic countries. For instance, eutrophication has affected fresh waters particularly in southern Finland and Sweden, while acidification has caused much damage in Norway and Sweden (Hesthagen et al., 1999; Tammi et al., 2003).

An overview of freshwater resources, their fish fauna, and fisheries in Finland, Norway and Sweden

Finland, Norway and Sweden are situated on the Fennoscandian shield between the latitudes 55°N and 70°N, where rocks are acidic due to high SiO2 content. The three countries together have 126500 lakes larger than four hectares (Table 1), of which about 8600 have a surface area exceeding 1 km2, and 78 are larger than 100 km2 (Henriksen et al., 1997). In Finland and Sweden, approximately 10% of the surface area is freshwater, whereas in the area in Norway is about 6%. The Nordic lakes exhibit great variety in size, depth, morphometry, trophic status and flora and fauna.

Table 1.

The number size distribution of lakes in Finland, Norway and Sweden (Henriksen et al. 1997).

Lake area km2
 0.04–0.1 0.11–1.0 1.01–10 10.01–100 > 100 Total 
Finland 14717 12311 2164 276 47 29515 
Norway 20218 16417 2039 164 38845 
Sweden 34126 20086 3511 372 24 58122 
Total 69064 48814 7714 812 78 126482 
Lake area km2
 0.04–0.1 0.11–1.0 1.01–10 10.01–100 > 100 Total 
Finland 14717 12311 2164 276 47 29515 
Norway 20218 16417 2039 164 38845 
Sweden 34126 20086 3511 372 24 58122 
Total 69064 48814 7714 812 78 126482 

The mountains of Scandinavia form an effective barrier for colonization of most fish species. Finland and southern Sweden are mostly covered by plains and areas with forests and numerous lakes. Norway and large areas of Sweden and northernmost Finland are mountains with numerous small lakes and streams. The climate is influenced by the North Atlantic current, and in the west the climate is more mild and temperate; whereas in the east the climate is more continental with cold winters and warm summers.

Water chemistry is closely related to geology, soil thickness, precipitation and hydrology (Henriksen et al., 1998). The chemistry of the lakes is characterized by low ionic strength, with low concentrations of the nutrients nitrogen and phosphorus. There are general differences in the lake water chemistry between the countries, due to differences in hydrology, precipitation, chemistry, hydrology, soil cover and vegetation. There is a precipitation gradient from western Norway (annual precipitation range between 2000–3000 mm) to eastern Finland (annual precipitation approximately 300 mm) and a soil composition gradient from mountain areas with thin and patchy soils to forested areas with thicker soils. These two factors are reflected in lake water chemistry with low concentrations of base cations, alkalinity and total organic carbon (TOC) in the west to higher concentrations in the east. Median values for base cation concentrations are on average three times higher in Sweden and Finland than in Norway, while TOC concentrations vary even more (Henriksen, Skjelvale, Mannio, Wilander, Jensen et al., 1997).

Historically the most dramatic changes in the Nordic lakes and rivers occurred after the onset of the Industrial Revolution in the 18th century. The growing need for cultivated land leads to the drainage and water level lowering in many lakes. During the 20th century, a large number of lakes are regulated. Anthropogenic processes have accelerated and in particular acidification and eutrophication have influenced many inland waters. Today, Nordic lakes and rivers are used for fisheries, waste disposal, water supply, industrial processes, transportation, irrigation, recreation, and hydroelectric power generation. There are practically no totally unimpacted lakes and rivers in the area.

Freshwater fish fauna

The fish fauna of Finland, Norway and Sweden consists of 56 species reproducing in freshwaters, including four species of the family Petromyzonidae (Table 2). These figures include 13 introduced, originally alien species to the Nordic countries which form self-sustaining populations. Finland has 43, Sweden 46, and Norway 43 fish species that are presently reproducing in fresh waters.

Table 2.

Native (NA), introduced (IN), maintained by continuous stockings (ST) and extinct (EX) fishes spawning in freshwaters in Finland, Norway and Sweden.

FinlandNorwaySweden
Common name Scientific name NA IN ST EX NA IN ST EX NA IN ST EX 
River lamprey Lampetra fluviatilis          
Brook lamprey Lampetra planeri          
Arctic lamprey Lampetra japonica            
Sea lamprey Petromyzon marinus           
Sturgeon Acipenser sturio           
Atlantic salmon Salmo salar          
Brown trout Salmo trutta          
Vendace Coregonus albula          
Whitefish Coregonus lavaretus          
Peled whitefish Coregonus peled           
Arctic charr Salvelinus alpinus          
Brook trout Salvelinus fontinalis          
Lake trout Salvelinus namaycush          
Rainbow trout Oncorhynchus mykiss          
Pink salmon Oncorhynchus gorbuscha           
Sockeye salmon Oncorhynchus nerka            
Cutthroat trout Oncorhynchus clarki            
Grayling Thymallus thymallus          
Smelt Osmerus eperlanus          
Pike Esox lucius          
Roach Rutilus rutilus          
Dace Leuciscus leuciscus          
Chub Leuciscus cephalus          
Ide Leuciscus idus          
Minnow Phoxinus phoxinus          
Rudd Scardinius erythropthalmus          
Asp Aspius aspius          
Tench Tinca tinca          
Gudgeon Gobio gobio          
Bleak Alburnus alburnus          
Sunbleak Leucaspius delineatus          
Bream Abramis brama          
White bream Abramis bjoerkna          
Blue bream Abramis ballerus           
Vimba bream Vimba vimba           
Ziege Pelecus cultratus           
Carp Cyprinus carpio          
Crucian carp Carassius carassius          
Gibel carp Carassius gibelio            
Goldfish Carassius auratus           
Grass carp Ctenopharyngodon idella            
Stone loach Barbatula barbatula           
Spined loach Cobitis taenia           
Brown bullhead Ameiurus nebulosus           
Sheatfish Silurus glanis           
Burbot Lota lota          
Three spined stickleback Gasterosteus aculeatus          
Nine spined stickleback Pungitius pungitius          
Brook stickleback Culaea inconstans            
Bullhead Cottus gobio          
Alpine bullhead Cottus poecilopus          
Four-horned sculpin Triglopsis quadricornis          
Perch Perca fluviatilis          
Pikeperch Sander lucioperca          
Ruffe Gymnocephalus cernuus          
Pumpkinseed Lepomis gibbosus            
TOTAL  37 32 11 41 
FinlandNorwaySweden
Common name Scientific name NA IN ST EX NA IN ST EX NA IN ST EX 
River lamprey Lampetra fluviatilis          
Brook lamprey Lampetra planeri          
Arctic lamprey Lampetra japonica            
Sea lamprey Petromyzon marinus           
Sturgeon Acipenser sturio           
Atlantic salmon Salmo salar          
Brown trout Salmo trutta          
Vendace Coregonus albula          
Whitefish Coregonus lavaretus          
Peled whitefish Coregonus peled           
Arctic charr Salvelinus alpinus          
Brook trout Salvelinus fontinalis          
Lake trout Salvelinus namaycush          
Rainbow trout Oncorhynchus mykiss          
Pink salmon Oncorhynchus gorbuscha           
Sockeye salmon Oncorhynchus nerka            
Cutthroat trout Oncorhynchus clarki            
Grayling Thymallus thymallus          
Smelt Osmerus eperlanus          
Pike Esox lucius          
Roach Rutilus rutilus          
Dace Leuciscus leuciscus          
Chub Leuciscus cephalus          
Ide Leuciscus idus          
Minnow Phoxinus phoxinus          
Rudd Scardinius erythropthalmus          
Asp Aspius aspius          
Tench Tinca tinca          
Gudgeon Gobio gobio          
Bleak Alburnus alburnus          
Sunbleak Leucaspius delineatus          
Bream Abramis brama          
White bream Abramis bjoerkna          
Blue bream Abramis ballerus           
Vimba bream Vimba vimba           
Ziege Pelecus cultratus           
Carp Cyprinus carpio          
Crucian carp Carassius carassius          
Gibel carp Carassius gibelio            
Goldfish Carassius auratus           
Grass carp Ctenopharyngodon idella            
Stone loach Barbatula barbatula           
Spined loach Cobitis taenia           
Brown bullhead Ameiurus nebulosus           
Sheatfish Silurus glanis           
Burbot Lota lota          
Three spined stickleback Gasterosteus aculeatus          
Nine spined stickleback Pungitius pungitius          
Brook stickleback Culaea inconstans            
Bullhead Cottus gobio          
Alpine bullhead Cottus poecilopus          
Four-horned sculpin Triglopsis quadricornis          
Perch Perca fluviatilis          
Pikeperch Sander lucioperca          
Ruffe Gymnocephalus cernuus          
Pumpkinseed Lepomis gibbosus            
TOTAL  37 32 11 41 

Due to geographical differences, the freshwater fish fauna differs considerably in the northern and southern parts of the Nordic countries but the species richness increases also from west to east (Figure 2, Tammi et al., 2003). Large lakes in southern Finland and Sweden have generally 15–20 fish species (mainly percids, cyprinids and salmonids); whereas in the north the number of species is usually less than ten. Small forest lakes usually have only 1–4 species which in southern parts are perch, pike and roach. In the north the most common species are perch, pike, grayling, whitefish, brown trout, Arctic charr and burbot. Whitefish, brown trout, pike, minnow, perch, nine-spined stickleback (Pungitius pungitius) and perch live in all parts of Finland (Urho and Lehtonen, 2008). In Swedish lakes, the most common fish species are perch, roach and pike, and brown trout, minnow and alpine bullhead in rivers and streams (Swedish Board of Fisheries; National Registry of survey test fishing; NORS, and Swedish Electrofishing RegiSter, SERS).

Figure 2.

Regional distribution of the mean number of fish species per lake according to the Fish Status Survey of Nordic Lakes (Rask et al., 2000; Tammi et al., 2003) indicating a north-south and east-west gradient in the species richness. The lakes for the survey were selected using a procedure of stratified random sampling to ensure a sufficient representation of lakes from different parts of the countries and from different size classes. The information on fish status of selected lakes, 4900 altogether, was gathered by mail survey questionnaires.

Figure 2.

Regional distribution of the mean number of fish species per lake according to the Fish Status Survey of Nordic Lakes (Rask et al., 2000; Tammi et al., 2003) indicating a north-south and east-west gradient in the species richness. The lakes for the survey were selected using a procedure of stratified random sampling to ensure a sufficient representation of lakes from different parts of the countries and from different size classes. The information on fish status of selected lakes, 4900 altogether, was gathered by mail survey questionnaires.

Most of the species in Norway are only found in the southeast; while a few species have been able to reach northern areas through Swedish and Finnish watercourses. These include pike, whitefish, grayling, perch, burbot, minnow and alpine bullhead. Brown trout, Arctic charr, three spined stickleback and nine spined stickleback probably reached this region from the west. The distribution area of some native fish species has also expanded considerably during the recent decades to areas where brown trout was the only fish species present. This is especially the case for the minnow, partly because anglers have used this species as live bait (Hesthagen and Sandlund, 2006).

Northern ranges of species are determined primarily by climate, especially temperature. This alone restricts some species, e.g. chub (Leuciscus cephalus), vimba bream (Vimba vimba), asp (Aspius aspius), rudd (Scardinius erythropthalmus), blue bream (Abramis ballerus), tench (Tinca tinca) and gudgeon (Gobio gobio) to the south. On the other hand, some fish species, such as Arctic char live only in the northern and high altitude lakes and in some deep oligotrophic lakes of southern and central Finland and Sweden. Species which have not extended their range to watersheds running to the Arctic Ocean include e.g. brook lamprey (Lampetra planeri), vendace, Crucian carp (Carassius carassius), roach (Rutilus rutilus), dace (Leuciscus leuciscus), ide (Leuciscus idus), bleak (Alburnus alburnus), bream (Abramis brama), ruffe (Gymnocephalus cernuus) and bullhead (Cottus gobio).

The anadromous migratory fish species, salmon, brown trout, anadromous whitefish, vimba bream, sea lamprey (Petromyzon marinus) and lamprey (Lampetra fluviatilis) spawn in rivers and mostly grow at sea. Catadromous eel (Anguilla anguilla) and flounder (Platichthys flesus) spawn at sea and may grow up in the sea or in fresh waters. These fish species have also suffered from environmental changes, such as damming and pollution.

Freshwater fisheries

Fishing has always played an important role in the daily life of people in Nordic countries, and the numerous lakes and watercourses offer good opportunities for many kinds of fishing. In 2004, the proportion of recreational fishermen in Norway, Finland and Sweden was about 50, 40 and 27% of the total population respectively (Toivonen et al., 2000). In three Nordic countries, the fishing rights belong to the water or land owner with some exceptions. In Finland, fishers between ages 18–64 years have to buy a licence either from the state or from the water owner. For people under 18 and over 64 years, ice angling and angling with natural bait and fishing with spinning rod or fly rod are free public rights. In Sweden, all citizens are allowed to fish in waters owned by the state, but the fishery legislation gives some geographic restrictions and that of methods used. In Norway, the land owner normally gives permission to individual fishermen through the sale of fishing licenses. The state owns about 50% of the Norwegian area, particularly large areas in the north. There are public regulations concerning gear, fishing times etc. particularly for salmon fishing (Toivonen et al., 2000). In Norway, young people under 16 years and in Finland and Sweden under 18 years of age are allowed to fish with a rod without a license in non-anadromous waters.

A Nordic speciality is the wide use of gill nets, traps and other fishing gears which in most western countries are used only by professional fishermen. However, when measured by the number of fishermen, the most popular gears are hook and line which are used by about two thirds of the fishermen. The total catch by recreational fishers amounted to over 38 million kg in 2004 of which almost 80% was caught in lakes and rivers. In 2004, 53% of recreational catch was caught with gill nets, trap nets and fish traps and the rest with rod and line (Finnish Game and Fisheries Research Institute, 2005). In Sweden and Norway, most of the recreational fish catch in freshwater are captured with rod and line, but nets are also widely used.

There are some professional fishermen in inland lakes in all three countries, although the number has decreased sharply during recent decades. In Finland there were less than 1000 professional freshwater fishers in 2005, which is a reduction of about 50% during the last 20 years. Fishing today is concentrated on a few fish species; mainly vendace, whitefish, pikeperch and perch in large lakes (e.g. Saimaa, Päijänne, Inari and Puruvesi). In Sweden, the number of professional freshwater fishermen is about 160, and 86% of the catches are caught in the four large lakes (Mälaren, Hjälmaren, Vättern and Vänern). The most important target species are pikeperch, vendace, perch, eel and whitefish. In Norway, there are probably less than 10 professional fishermen with main income from inland fisheries.

Public interest in recreational fishing is big in these countries; in particular tourism based on fisheries is expected to grow in the future in contrast to other segments of the fisheries sector. However, socio-economic issues and increased urbanization will probably impact recreational fishing. Instead of the older main goal of getting food, many people are now looking for new experiences in unexploited nature and are prepared to pay for these. At the same time the discussion on the ethics of fishing is growing and increased concern is targeted to animal welfare. Changes in the political environment and the EU common fisheries policy will likely also impact recreational fisheries.

Freshwater habitats—effects of human-induced environmental changes

Nutrient loads

In the Nordic countries nutrient loads from point sources have decreased during recent decades. This development can also be seen in the response of fish communities. Some 30–40 years ago, waters close to many cities or industrial plants were heavily polluted and had only limited recreational or fisheries value (Hakkari, 1992). Today they are often inhabited by healthy and catchable fish populations and communities. However, there are a number of highly eutrophic lakes in agricultural areas of southern and western Finland and Sweden that regularly suffer from algal blooms and have high biomasses of less valuable cyprinid fish. It was estimated that the number of eutrophic lakes dominated by cyprinid fish species in Finland and Sweden were 2260 and 1050, respectively, whereas Norway has no such lakes (Tammi et al., 2003). Nutrient loads have also affected the water quality and biota of many rivers. This is especially the case, for instance rivers flowing through agricultural areas in southern and western Finland and Sweden.

Although agriculture is the main source of nutrient load to the surface waters in Finland and Sweden, forestry is a leading activity in catchments covering almost the whole country. Of the most common fish species, perch, pike and roach are all capable of completing their life cycle in shallow waters and with varying environmental conditions. Therefore, no direct effects of catchment forestry on these fish have been recorded despite changes in water quality, primary productivity, zooplankton and zoobenthos at some experimental sites (Rask et al., 1998). These changes were interpreted as affecting fish indirectly. Most obvious direct effects of forestry-induced habitat changes on fish populations have taken place in some larger lakes in eastern Finland inhabited by species like vendace and burbot, which favour cold and oxygen-rich water and need hard bottom substrates for spawning. Intensive forestry including clear cutting, ploughing and ditching increases the nutrient loads and sedimentation of spawning grounds and decreases the oxygen concentrations near the bottom, thus damaging the fish populations. These forestry activities have also widely destroyed the habitats of fish in brooks and small rivers.

The first step in mitigating the effects of eutrophication is the reduction of external nutrient load. However, there are some seriously eutrophic water bodies with high internal phosphorus loads, which makes their restoration very challenging. In 1970–1995, the most popular methods for the restoration of eutrophicated lakes were hypolimnetic aeration, macrophyte harvesting and water level raising. As a consequence of some successful joint management and research projects, lake restoration by the mass removal of cyprinids, especially the roach has become a common method during the last 15 years (Sarvala et al., 2000). In these projects, the general goals have been to improve the water quality, recreational and fishery values of the lakes. Today, there are some projects in operation in larger lakes with more fisheries oriented goals: to remove less valuable cyprinids thereby to increase the vendace stock and enhance the potential for professional fishing.

Atmospheric loads

In the late 1960s, it was shown that the increasing acidification problem of oligotrophic lakes was related to long distance air pollution (Odén, 1968). By the 1970s severe damage to fish populations was recognised in the Nordic countries. It was estimated that acidification has affected the abundance of 2200–4400 fish populations in Finland (Rask et al., 1995). Almost 60% of the affected or lost populations were roach, the most acid sensitive of the common fish species in small lakes. Also populations of perch, pike, ruffe and burbot were affected. In Norway, acidification has damaged and wiped out about 5400 and 9600 fish populations in lakes > 3.0 ha, respectively (Hesthagen et al., 1999). Brown trout have suffered the largest damage, as about 3900 and 8200 populations have been lost, respectively. Perch is the second most severely affected species after brown trout and nearly 1800 populations have been affected or lost.

In Sweden, acidification has deteriorated the ecological status of numerous lakes and watercourses, in particular in the western part of the country. To restore these waters, an extensive liming programme was initiated in 1976 and has been continuing ever since. About 100 lakes and watercourses have been limed annually within the national programme.

In Norway, a governmental programme of liming was initiated in 1983 (Sandøy and Romunstad, 1995). During the early 1990s, this involved annual liming of about 2000 lakes. Further, Atlantic salmon became virtually extinct in at least 25 rivers as a result of acidification (Hesthagen and Hansen, 1991). A total of 22 acidified rivers are now limed to re-establish or restore Atlantic salmon. The catches of salmon in these rivers now constitute about 10% of the total catch of wild salmon in Norwegian rivers. In Finland there has been no national liming programme.

Due to the successful reduction of emissions, sulphate deposition has decreased in Europe. The positive development has continued since the late 1970s. The first signs of chemical recovery of acidic lake waters, in the form of decreases in sulphate concentrations and increases in pH and alkalinity were recorded in the early 1990s. At the same time, the first records of abundant year-classes of perch were made in acidified lakes of southern Finland (Nyberg et al., 1995).

There has been a substantial improvement in water quality of lakes in southern Norway, Sweden and Finland, with increased pH, lower concentrations of inorganic aluminium and higher acid neutralizing capacity (ANC) (Skjelkvåle et al., 2005). It is therefore expected that fish populations can be re-established in the formerly acidified lakes. However, there has been a pronounced increase in total organic carbon (TOC) of surface waters in the Nordic countries in recent years, similar to that observed elsewhere in Europe and North America (Skjelkvåle et al., 2005; Evans et al., 2005). High-TOC lakes are more acidic and have higher concentrations of toxic inorganic aluminium with respect to ANC than low-TOC lakes. Thus, a higher ANC will be needed to obtain non-toxic water quality if TOC levels continue to increase.

The precipitation of mercury compounds has decreased during the last two decades. However, no decreasing trend has been observed so far in pike of remote areas in Finland; though pike mercury concentrations have decreased in waters downstream (Verta et al., 2002). Increased leakage from forest areas after windfalls caused by winter storms may increase mercury enrichment in predatory fish species in the future.

The nuclear power plant accident in Chernobyl in 1986 caused remarkable radioactive fallout in some parts of the Nordic countries. In certain sensitive lake systems in southern and western Finland the 137Cs activity rose to levels of 10000 Bq kg−1 in perch and up to 30000 Bq kg−1 in pike (Saxén, 2007). Since then the radioactivity has dropped sharply but fairly high levels can still be measured in some lakes, although recommendations to restrict the human fish consumption have been removed. Fish in lakes in large areas of central and southern Norway had > 1500 Bq kg−1 wet weight, but levels of between 20000 and 30000 Bq kg−1 wet weight were also reached (Forseth et al., 1991). Studies conducted in 2006 showed a considerable reduction in radiocaesium in fish in South Norway, mainly with concentrations < 400 Bq kg−1 wet weight (Ola Ugedal, pers. comm.).

Degradation of fish habitats due to engineering

In Finland, there are more than 200 regulated natural lakes and some 30 artificial lakes larger than 1 km2. This is less than 1% of the number but about 30% in terms of total lake area. The regulation of lakes has been extensive also in Sweden and some 2500 lakes have been regulated (Fiskeriverket, 2004). In Norway there are 876 reservoirs covering about 30% of the total lake area.

In northern Finland the main reason for lake regulation is hydropower production, whereas in the south regulation is mainly for general water services and flood protection. Lake regulation impacts heavily on the littoral ecosystems and causes considerable negative impacts on feeding, reproduction, and nursery areas for fish. The main measure taken to compensate for the damages to fishing has been fish stocking.

To compensate for reproduction failure, hydropower companies are obliged to perform compensatory stocking of mainly anadromous salmonids in watercourses with hydroelectric power plants. In Sweden, about 2 million salmon smolts and about 700000 brown trout (sea trout) smolts are stocked in the Baltic Sea and on the west coast annually. In Finland, stocking with whitefish fingerlings, brown trout or rainbow trout of catchable size are common activities to increase the fisheries value of dammed rivers. In the most extreme cases, natural rivers have been transformed to chains of the hydropower reservoirs. Consequently, the populations of migratory fish have been lost and many of the reservoirs now have cyprinid dominated fish communities (Vehanen, 1995). In Norway, 127 out of 146 salmon rivers (28%) are used for hydropower production. This has affected Atlantic salmon negatively and is the factor in 83 rivers (19%) (Hansen et al., 2006). Among 45 extinct populations of Atlantic salmon, hydropower production has been the main factor in 19 rivers.

In smaller rivers, the main reason for river modification was log transportation. Such activities changed the diversity of river habitats, especially the rapids, to homogeneous channels and resulted in destruction of fish habitats and many populations of salmonid fish. Even the smallest brooks, especially in southern and central Finland, have been subjected to dramatic changes. However, in recent years, fish habitats have improved. During the last two decades, many restoration projects began; and thus many of the channelized rivers and brooks have been restored.

Restoration of fish habitats

Most activities of fish habitat restoration in Finland, Sweden and Norway are directed at rivers. The operations needed are always site dependent, but typically include construction of spawning sites and nursery areas, the removal of possible migration obstacles, regulating the fishing so that a sufficient number of parent fish can migrate to their natal rivers, and/or restoration of the catchment area to decrease the load of solid substances.

Within the national Swedish environmental objectives (Environmental Objectives Portal) the authorities have identified and drawn up action programmes for natural and cultural environments in, or in the vicinity of, lakes or streams that are of particularly high conservation value and require long-term protection.

Most activities towards fish habitat restoration in Norway are directed to canalised rivers. Only a few such restoration works have been carried out, starting in the 1980s (Hamarsland, 2001). Log driving was the main reason for canalising rivers, starting several hundred years ago. Restoration work has now started in some rivers to create more complex river bottoms by adding stones. In areas with clay, stones have been added to the river bed and along the river sides to reduce the erosion rate (Jonsson et al., 2001). In lakes there is a need for fish habitat restoration, for example, due to permanent lowering of lake water levels and regulation for hydropower production. Most common activities are restoration of spawning grounds, the construction of spawning channels in regulated lakes, the construction of artificial spawning habitats, and manipulation of littoral vegetation to make it more diverse and thus offer nursery habitats for young fish. Also for lakes, the load of nutrients and solid substances from the catchments are restricted. In recent years the regulation practices of certain lakes have moved in a more ecological direction, leading to more natural rhythms of water level fluctuation.

Global change

Increased temperatures and changes in precipitation may affect freshwater fish populations over large areas in the northern hemisphere (Eaton and Scheller, 1996). Climate models for northern Europe indicate that mild and wet winters will occur more frequently in the next decades than today (Palmer and Räisänen, 2002). Changes in distribution, habitats and interactive processes between fish species will alter the composition of fish assemblages. Fishes live within complex webs of interactions and processes which include predator-prey interactions, competition and reproduction (Lehtonen, 1996). The impact of indirect processes, e.g. increased vegetation may alter the competitive prerequisites of different species and hence the species and size composition of the fish assemblages (DeAngelis and Cushman, 1990).

The ability of fish to adapt to changing environments is highly species-specific. The predicted climate change will be so rapid that all fish populations will not be able to adapt. Accordingly, three alternatives exist: (i) fishes may change their ranges, (ii) fishes may disappear from their present range or (iii) fishes may display evolutionary adaptations. It is likely that all three alternatives will occur (Lehtonen et al., 1992). From a population point of view the best alternative would be adaptation.

Fisheries management

Management practices in the three countries

Fisheries management includes several tools: e.g. regulations on use and structure of fishing gear, temporal and regional fishing restrictions, the size limits of target fish, the limitations of fishing efficiency, and amount of catch. The general goal is to meet the principle of sustainable use of natural resources. This can be reached assuring a sufficient size of the spawning stock of the target species and allowing the spawning at least once but preferably several times. At present, this requirement is not fulfilled in most fisheries of the large predatory fish, such as pikeperch, pike, brown trout, Atlantic salmon and Arctic char.

Fish stocking

Stocking has traditionally been one of the cornerstones of Nordic fisheries management. For example, the total number of stocked fish in Finland in 2004 was 125 million individuals, of which about 92 million were newly hatched. 27 million were one summer old and the rest older than one year (Finnish Game and Fisheries Research Institute, 2005). The most important stocked species were whitefish (ca 18 million individuals), pikeperch, salmon, brown trout and grayling (8, 2.5, 1.1 and 1.6 million individuals, respectively). Also some foreign species are stocked regularly, namely peled whitefish, brook trout, rainbow trout, lake trout and common carp.

Also in Sweden, stocking for fisheries and stock enhancement purposes has been extensive (Pakkasmaa and Petersson, 2005). Several hundreds of introductions are performed yearly. Rainbow trout is the most common species used mainly for put-and-take fisheries. The most common native species used for stockings is brown trout.

In Norway, freshwater fish have been transported between localities for stocking purposes for at least 1000 years. Brown trout is the most common species, whereas Arctic char and grayling are rarely stocked. In the eastern part of Norway, brown trout have been stocked into at least 1400 localities during recent decades and thus the total stocked with brown trout throughout the entire country may total between 5000 and 10000 localities. Since 1992, the legislation has required that the fish be raised and stocked in the same watershed.

Introduction of alien species

A total of 13 alien species which are reproducing now exist in Nordic watersheds. Common carp was introduced during the 15th century. The other species were introduced between early 1800 and 2005. Five North American salmonids have been introduced and have established reproducing populations; brook trout, rainbow trout, pink salmon, chum salmon and lake trout. Pink and chum salmon were spread in northern Norwegian rivers in the late 1950s and early 1960s (Hesthagen and Sandlund, 2007) after being introduced to rivers on the Kola Peninsula in Russia (Dushkina, 1994). Brook trout and rainbow trout were introduced in the late 1800s and early 1900s to many lakes in all three countries. Lake trout was released in the 1970s to all three countries.

Peled whitefish was introduced into Finnish waters in the mid 1960s and it has established in some reservoirs in northern areas. In addition, grass carp (Ctenopharyngodon idella), goldfish (Carassius auratus), gibel carp (Carassius auratus m.gibelio), pumpkinseed (Lepomis gibbosus) and brown bullhead (Ameiurus nebulosus) have been introduced.

Conclusions

The Nordic countries have plenty of fresh waters, but only 4 lamprey species and 52 bony fish species are known to reproduce regularly in the Nordic rivers and lakes. Anthropogenic influence on fish fauna and its environment has been much wider and more profound than natural changes. Migratory species especially, mostly salmonid stocks, have experienced the biggest damage due to dredging and damming of rivers. On the other hand, water quality of many lakes subject to point loads of nutrients has improved in recent decades. This development has also resulted in recovery of fish communities and improvement of fishing possibilities.

Traditionally, the main measure in compensating the damaged fish stocks in Nordic countries has been through stocking. However, fisheries management includes several tools. Today the direction is towards improving the possibilities of natural reproduction of fish, and the overall goal of the fisheries policy is the sustainable use of natural resources.

Global change will probably shift Nordic fish assemblages to cyprinid and percid dominance together with the decrease and even the collapse of salmonid and other coldwater fish populations. Some observations indicate that changes are already taking place in the spawning and hatching times of certain coldwater adapted species, like burbot and whitefish. On the other hand, the spreading of native species through stockings has been intensive and one or more non-native species have been introduced in one third of the Nordic lakes.

References

DeAngelis, D. L. and Cushman, R. M.
1990
.
Potential application of models in forecasting the effects of climate change on fisheries
.
Trans. Am. Fish. Soc.
,
119
:
224
239
.
Dushkina, L. A.
1994
.
Farming of salmonids in Russia
.
Aquaculture and Fisheries Management
,
25
:
121
126
.
Eaton, J. G. and Scheller, R. M.
1996
.
Effects of climate warming on fish thermal habitat in streams of the United States
.
Limnology and Oceanography
,
41
:
1109
1115
.
Environmental Objectives Portal 2007
Evans, C. D., Monteith, D. T. and Cooper, D. M.
2005
.
Long-term increases in surface water dissolved organic carbon: Observations, possible causes and environmental impacts
.
Environ Pollut
,
137
:
55
71
.
Forseth, T., Ugedal, O., Jonsson, B., Langeland, A. and Njåstad, O.
1991
.
Radiocaesium turnover in Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in a Norwegian lake
.
J. Applied Ecology
,
28
:
1053
1067
.
Finnish Game and Fisheries Research Institute
.
2005
.
Recreational fishing 2004
62
SVT Agriculture, Forestry and Fishery 2005
Hakkari, L.
1992
.
Effects of pulp and paper mill effluents on fish populations in Finland
.
Finnish Fisheries Research
,
13
:
93
106
.
Hamarsland, A.
Country status report- Norway
.
Proceedings from the CONNECT-workshop: Physical habitat restoration in canalised watercourses – possibilities and contraints
.
Nov 6–8 2006
. Edited by: Taugbøl, T. and L'Abée-Lund, J. H. pp.
62
64
.
NVE Report 7-2001, Oslo
Hansen, L. P., Fiske, P., Holm, M., Jensen, A. J. and Sægrow, H.
2006
.
Bestandsstatus for laks. Rapport fra arbeidsgruppe
Utredning for DN 2006-3. (State of Salmon stocks. Working group report. In Norwegian)
Henriksen, A, Skjelvale, B. L., Mannio, J., Wilander, A., Harriman, R., Curtis, C., Jensen, J. P., Fjeld, E. and Moissenko, T.
1997
.
Northern European lake survey, 1995
.
Ambio
,
27
:
80
91
.
Henriksen, A., Skjelvale, B. L., Mannio, J., Wilander, A., Jensen, J. P., Moiseenko, T., Harriman, R., Traaen, T. S., Fjeld, E., Vuorenmaa, J., Kortelainen, P. and Forsius, M.
1997
.
Results of national lake surveys 1995 in Finland
Norway, Sweden, Denmark, Russian Kola, Russian Karelia, Scotland and Wales. NIVA Report SNO 3645-97
Hesthagen, T. and Hansen, L. P.
1991
.
Estimates of the annual loss of Atlantic salmon (Salmo salar L.) in Norway due to acidification
.
Aquacult. Fish. Manage.
,
22
:
85
91
.
Hesthagen, T. and Sandlund, O. T.
2006
.
Phoxinus phoxinus
Nobanis–Invasive Alien Species Fact Sheet. www.nobanis.org
Hesthagen, T. and Sandlund, O. T.
2007
.
Non-native freshwater fishes in Norway: history, consequences and perspectives
.
J. Fish. Biol.
,
71
:
173
183
.
Hesthagen, T., Sevaldrud, I. H. and Berger, H. M.
1999
.
Assessment of damage to fish populations in Norwegian lakes due to acidification
.
Ambio
,
28
:
12
17
.
Jonsson, N., Aagaard, K., Jonsson, B., Bongard, T., Hanssen, O. and Berger, H. M.
2001
. “
Hvordan påvirker steinsetting av elvebunn ørret- og bunndyrfaunaen i et vassdrag? (What kind of impacts does stone placement have on local brown trout and benthos in a water body? In Norwegian)
”. In
NINAs strategiske instituttprogrammer 1996–2000. Virkninger av fysiske naturinngrep–systemøkologisk innretting. Sluttrapport.
Edited by: Heggberget, T. M. and Jonsson, B.
18
31
.
NINA Temahefte 16. Trondheim. (NINAs strategic institute programmes 1996–2000. Effects of man-made physical disturbance. Systems ecology final report. In Norwegian)
Lehtonen, H.
1996
.
Potential effects of global warming on northern European freshwater fish and fisheries
.
Fish. Mgmt. Ecol.
,
3
:
59
71
.
Lehtonen, H., Lappalainen, J., Forsman, L., Soivio, A., Urho, L., Vuorinen, P. J. and Tigerstedt, C.
1992
.
The effects of climate change on fishes, aquaculture, fish stocks and fishing
.
A review of the literature. RKTL, Kalatutkimuksia-Fiskundersökningar
,
47
:
1
119
.
Nyberg, K., Raitaniemi, J., Rask, M., Mannio, J. and Vuorenmaa, J.
1995
.
What can perch population data tell us about the acidification history of a lake?
.
Water Air Soil Pollut.
,
85
:
395
400
.
Odén, S.
1968
. “
The acidification of air precipitation and its consequences in the natural environment
”. In
Ecology Committee Bulletin No. 1. Swedish national Science Research Council, Stockholm
,
Arlington, Virginia, , USA
:
Translation Consultants Ltd.
.
Pakkasmaa, S. and Petersson, E.
2005
.
Fisk i fel vatten (Fish in wrong waters.), Finfo 2005, 9. Swedish Board of Fisheries 2005 (in Swedish with English and Finnish summaries)
Palmer, T. N. and Räisänen, J.
2002
.
Quantifying the risk of extreme seasonal precipitation events in a changing climate
.
Nature
,
415
:
512
514
.
Rask, M., Appelberg, M., Hesthagen, T., Tammi, J., Beier, U. and Lappalainen, A.
2000
.
Fish status survey of Nordic lakes–species composition, distribution, effects of environmental changes
508
Tema Nord 2000
Rask, M., Mannio, J., Forsius, M., Posch, M. and Vuorinen, P. J.
1995
.
How many fish populations in Finland are affected by acid precipitation
.
Env. Biol. Fish.
,
42
:
51
63
.
Rask, M., Nyberg, K., Markkanen, S.-L. and Ojala, A.
1998
.
Forestry in catchments: effects on water quality, plankton, zoobenthos and fish in small lakes
.
Boreal Env. Res.
,
3
:
75
86
.
Sandøy, S. and Romunstad, A. J.
1995
.
Liming of acidified lakes and rivers in Norway. An attempt to preserve and restore biological diversity in the acidified regions
.
Water, Air and Soil Pollution
,
85
:
997
1002
.
Sarvala, J., Helminen, H. and Karjalainen, J.
2000
.
Restoration of Finnish lakes using fish removal: changes in the chlorophyll-phosphorus relationship indicate multiple controlling mechanisms
.
Verh. Internat. Verein. Limnol.
,
27
:
1473
1479
.
Saxén, R. L.
2007
.
137Cs in freshwater fish and lake water in Finland after the Chernobyl deposition
.
Boreal Env. Res.
,
12
:
17
22
.
Skjelkvåle, B. L., Stoddard, J. L. and Jeffries, D. S.
2005
.
Regional scale evidence for improvement in surface water chemistry 1990-2001
.
Environ. Poll.
,
137
:
165
176
.
Tammi, J., Appelberg, M., Hesthagen, T., Beier, U., Lappalainen, A. and Rask, M.
2003
.
Fish status survey of Nordic lakes: effects of acidification, eutrophication and stocking activity on present fish species composition
.
Ambio
,
32
:
98
105
.
Toivonen, A.-L., Appelblad, H., Bengtsson, B., Geertz-Hansen, P., Gu∂ Gu∂ bergsson, G., Kristofersson, D., Kyrkjebo, H., Navrud, S., Roth, E., Tuunainen, P. and Weissglas, G.
2000
.
Economic value of recreational fisheries in the Nordic countries
604
TemaNord 2000
Urho, L. and Lehtonen, H.
2008
.
Fish species in Finland
Riista- ja kalatalous, selvityksiä 1B/2008
Vehanen, T.
1995
.
Fisheries conditions in constructed rivers
Fish Studies 91, Finnish Game and Fisheries Research Institute
Verta, M., Rissanen, J., Porvari, P. and Jälkö, L.
2002
.
Monitoring mercury in fish
,
Technical report, Finnish Environment Institute
.