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.

Avsikten är att detta arbete skall ske gemensamt av Fiskeriverket och Laxforskningsinstitutet. Inom Fiskeriverket sker samordningen och dataläggningen vid Sötvattenslaboratoriet, Örebro, medan Fiskeriverkets utredningskontor skall svara 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 were compiled from several different authorities, e.g. different counties, communities, sport fishingsassociations, the Salmon Research Institute and the National Board of Fisheries. The stock data consist of electrofishing results, fish ladder counts, fishing statistics and stockings from rivers. From the four greatest lakes data consist of fishery statistics, preyspecies abundances (hydroacoustics) and stockings. Environmental data added weretemperature, water quality and water flow.

Anadromous salmon and trout on the Swedish west coast have increased considerably due to liming, elimination of migratory obstacles and a reduced sea fishery (e.g.Figures 4 & 5 showing number of parr/100m2 in Rivers Ätran and Fylleån, respectively). During the period 1990-95 drought and following low discharge has been a problem reducing parr abundances. Intensified monitoring is suggested in the future.

Due to overexploitation by the sea and coastal fishery, natural anadromous salmon and trout stocks in the Baltic are below acceptable levels, with increasing risk of genetic detonation and considerable economic losses. For salmon the effects of the M74 syndrome, i.e. excessive fry mortality, has further reduced the stocks. Figure 19 shows the average mortalities of fry from hatcheries at salmonrivers running to the Gulf of Bothnia.

The total catch must decrease, especially the catch with drift nets and lines in the open sea, which is carried out on mixed stocks.

Lake resident salmon occur naturally only in Lake Vänern, where the two stocks have suffered heavily from the building of dams for hydroelectric purposes. The natural stocks have been declared to be of national interest. 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 with increased closed areas are measures that have improved the conditions for the stocks in the last years.

Trout populations in inland waters have generally increased on the west and east coast, while stocks in interior Sweden and in the mountain range have remained unchanged 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 230 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 (Coring’) together with whitefish (’sik’) and cisco (’siklöja’) dominate the catch (Figure 50). Roe from cisco contribute swith approximately 50% of the catch value.

In Lake Vättern the catch is dominated by salmon, Arctic char (’röding’) and whitefish (Figure 54 shows the catches since 1914). Stocking of salmon, a new species in the lake, gives a high yield; 600-1,000 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 Lake Mälaren (Figures 58, 60) and Hjälmaren (Figures 64, 65) eel (’ål’) and zander (pikeperch, ’gös’) are important species. The eel fishery 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 status of the crayfish (Astacusastacus) is given in chapter Crayfish (Kräftor). 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 Astacusastacus is considered an endangered species in southern Sweden, and restriction on stockings of the american crayfish has been imposed.

A drastic decline of the immigration of young eels have been noted in Swedish coastal rivers (Figure 71). 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 detoriate. In the last chapter (Biologisk mångfald) 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 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.