Swedish Agency for Marine and Water Management

Resursövervakningen av sötvatten, RASKA, bygger dels på Fiskeriverkets egna undersökningar, men till stora delar också på sammanställning av uppgifter framtagna av andra myndigheter, organisationer och ideella föreningar. RASKA är således beroende av beredvilligheten hos andra att dela med sig av sin information. Vår förhoppning är att sammanställningen och syntesen skall ge mer information än de olika delarna var för sig och att vi därigenom kan ge en samlad överblick över ett större antal vatten tillbaka till de enskilda uppgiftslämnarna.

Detta arbete sker gemensamt av Fiskeriverket och Laxforskningsinstitutet, LFI. Inom Fiskeriverket sker samordningen och dataläggningen vid Sötvattenslaboratoriet, Örebro, medan Fiskeriverkets utredningskontor och LFI svarar för dataleverans, materialanalys och syntesansvar vad gäller havsöring och lax.

The present report gives the status of fishpopulations in inland waters and coastal rivers in Sweden. The stock data consist of electrofishing results, fish ladder counts, fishing statistics and stockings from rivers. From the four greatest lakes data consist of fisherystatistics, prey species abundances (hydroacoustics) and stockings.

Anadromous salmon and trout on the Swedish west coast depend on liming. Salmon sea survival has declined. Added to these problems are increased occurrence of the parasite Gyrodactylus salaris and Danish experiments with delayed release of salmon in the southern Baltic. The latter has lead to increased contamination of natural spawningstocks with stocked salmon. The fishing on mixed salmon stocks must cease to improvethe number of spawners, especially in small populations. Brown trout stocks are stable.

Due to overexploitation by the sea and coastal fishery, natural anadromous salmonin the Baltic were below acceptable levels,with increasing risk of genetic deteriorationand considerable economic losses. Due to reduced TAC (total allowable catch) and reduced effects of the M74 syndrome, causing excessive fry mortality, stocks are slowly increasing. The situation for anadromous browntrout in the Baltic is unclear, but several small stocks are too heavily exploited by gillnetting close to river mouths.

Lake resident salmon occur naturally only in Lake Vänern, where the two remaining stocks have suffered heavily from the building of dams for hydroelectric purposes.The fishing is based on stocked fish, all without the adipose fin, while the few natural produced fish, i.e. with adipose fin left, are protected. Increased legal size together within creased closed areas are measures that have improved the conditions for the stocks in the last years, but both stocks must still be regarded as threatened.

Trout populations in inland waters have generally increased during the last two decades. Liming, habitat restoration and increased closed areas are considered the most important measures for the stocks in the future.

Approximately 200 commercial fishermen utilize the four great lakes (Vänern, Vättern, Mälaren, Hjälmaren). Detailed fishery statistics are collected on a monthly basis, including effort. In Lake Vänern salmon (’lax’) and trout (’öring’) together with whitefish (’sik’) and cisco (’siklöja’) dominate the catch. Roe from cisco contributes with approximately 50% of the catch value, but the population is presently declining. In Lake Vättern the catch is dominated by salmon, Arctic char (’röding’) and whitefish. Stocking of salmon, a new species in the lake, gives a high yield; 600-800 kg salmon/1,000 smolts released. Monitoring is carried out to study if the salmon stockings will have negative effects on the resident Arctic char, as the two species compete for the same prey species. In both lakes trolling for salmon and trout takes a large part of the total catch. In Lake Mälaren and Hjälmaren eel (’ål’) and zander (pikeperch, ’gös’) are important species. The eelfishery is completely dependent on stockings. In the former lake cisco was important until late 80’s, but then the population drastically declined, due to recruitment failure. The reason is not clear, but it coincides with warm winters with a short period with ice cover.

The status of the crayfish (Astacus astacus) is given in chapter 7. The crayfish plague was spread from Finland to Sweden in 1907 and many populations of the native crayfish have been eradicated. The plague later was further spread due to introduction of the American crayfish (Pacifastacus leniusculus).Today Astacus astacus is considered an endangered species in southern Sweden, and restriction on stockings of the American crayfish has been imposed. Due to the membership in EU the threat to the native species has increased as import of live exotic crayfish species has been allowed.

A drastic decline of the immigration of young eels have been noted in Swedish coastal rivers. This has lead to decreased Swedish catches in the Baltic, while the catches on the west coast have remained unchanged.

Fishery management must be carried out in such a way that biodiversity will not deteriorate. In chapter 9 biodiversity in stream populations is studied with the use of electrofishing data. Negative effects on biodiversity were mainly found in acidified waters and waters with extensive hydroelectric power development. It was concluded that biodiversity in general had remained unchanged or improved slightly during the last two decades, much thanks to liming and fishery management. A programme for monitoring of the biodiversity in the four great lakes has recently started, and preliminary results suggests that some non-commercial species need specific attention, e.g. river lamprey and Aspius aspius.