Northern Kattegat
Sand cover, eelgrass and anchor buoys
Between Stenungsund and Varberg, an extensive project is being carried out to improve habitats in large shallow bays, on clay and sandy bottoms, and on reefs and estuaries. The ecosystem will be strengthened through measures such as sand cover, replanting of eelgrass and installation of anchoring buoys to reduce damage to bottom vegetation. A large number of species will benefit from the measures, such as: salmon, eel, sea trout, pike, perch, terns, mussels, shells, bristle worms and crustaceans, as well as marine mammals such as harbor seals and gray seals.
Eelgrass meadows and their ecosystem services
Eelgrass meadows are important habitats in coastal ecosystems and provide several ecosystem services. They act as nurseries and shelters for many fish species, including eel, cod and sea trout. In addition, eelgrass stabilizes sediments, reduces erosion and improves water quality by trapping nutrients and particles.
Eelgrass beds also play an important role in carbon sequestration and contribute to climate change mitigation by sequestering carbon dioxide. In addition, they are part of the food web and benefit both commercially important fish stocks and biodiversity. The conservation and restoration of eelgrass beds is therefore crucial to maintaining ecosystem health and the ecosystem services they provide.
Stenungsund coast
The Stenungsund coast stretches from Stenungsön in the north to Timmervik in the south and is part of Hakefjorden. The area is protected by several nature reserves and is part of Natura 2000, with high value for both nature conservation and outdoor life. There are shallow bottoms here that are important for fish spawning, nursery areas and a rich bird life. The bottoms consist mainly of sand and clay, with elements of rocks and meadows.
Threats to the site
Threats include eutrophication, fisheries exploitation and pollution. Shallow waters are particularly vulnerable to jetties, dredging and hydrological changes, which increase sediment turbidity and degrade habitats.
Eelgrass is an important species in the area but has declined drastically since the 1980s. A conservation target is to have at least 205 hectares of eelgrass, but in 2015 only 125 hectares were covered and the area is likely to have declined further. In the southern part of the area, there are now only patchy stands. Losses are due to reduced light conditions, sediment turbidity and habitat changes caused by erosion, dredging, jetties and boating. Decreased predatory fish and increased algal growth exacerbate the situation.
Eelgrass planting
The project plans to restore eelgrass by covering a five-hectare area with sand to improve light conditions and planting 2.5 hectares of eelgrass. It is hoped that the measures will improve plant and animal life and create clearer water.
Previous trials in Tjörn have been successful, with a tenfold increase in eelgrass following sand cover and planting. At the same time, measures are planned outside the project in the rivers Anråse å and Rördalsån to benefit predatory fish such as sea trout, which can contribute to a more balanced ecosystem and improved conditions for eelgrass recovery.
Kungsbackafjorden
The project area “Norra Kattegatt” also includes Kungsbackafjorden in northern Halland – an important ecological area covering several watercourses, including Rolfsån, Kungsbackaån and Torpaån. The fjord is part of the Kungsbackafjorden Natura 2000 site, which covers 7,877 hectares and includes three nature reserves. Although the area is often referred to as a fjord, it is more correct to consider it as an estuary where freshwater from the rivers gradually mixes with saltwater. The area has both shallow bottoms and deep channels, as well as rich wildlife and large seagrass meadows.
The shallow waters serve as important spawning grounds for fish, especially flatfish fry and eels. Many fish species such as salmon, sea trout, mackerel, herring and cod fish move between the fjord and the sea. The deeper parts are dominated by soft bottoms with rich fauna, such as mussels, shells and polychaetes, which are important food sources for bottom-dwelling fish. The fjord has historically served as an area for cod reproduction.
A 2021 inventory showed that the distribution of eelgrass in the inner fjord has decreased by about 60 percent since 1999
Important fish species and eelgrass
Important species in the area are salmon, sea trout and sea lamprey. Eelgrass and dwarf eelgrass are particularly important to the ecosystem and act as nurseries for several species.
The conservation status of marine habitats in the area is generally poor according to the 2019 national assessment. The causes include eutrophication, environmental toxins and physical exploitation, such as construction, dredging and damage from boat traffic.
An inventory in 2021 showed that the distribution of eelgrass in the inner fjord has decreased by about 60 percent since 1999, mainly due to reduced depth distribution. Large amounts of filamentous algae and other signs of eutrophication are also present.
Enhancement measures
The project plans to improve water connectivity by removing and opening up piers and dredged material. These measures are expected to benefit habitats such as reefs, estuaries, large bays and straits, and exposed sand and mud bottoms. To protect eelgrass from damage, anchoring buoys will be installed in areas with high levels of small boat traffic. The buoys will be designed so that the rope or chain does not lie on the bottom at low water and cloud up. Information signs will be put up to raise awareness.
Survival of river pearl mussels depends on host fish
Barriers to migration
Removing migration barriers and opening up the river pearl mussel’s host fish, salmon and trout, will increase the species’ ability to reproduce. Barriers to migration come in many forms, from natural to man-made dams and power plants. In some cases, a good solution may be to build a wildlife passage to allow fish and other organisms to bypass the migration barrier.
Northern Kattegat
Latest news from the project area
Here you can read news about the target species and the actions being taken in the project area.
