There are few if any coastal areas left in the world that are not affected by human activities. Human activities affecting flads are for example ditching, agriculture and cutting forests as well as dredging and construction in the flads. All these activities affect the water quality in the flads and further the whole ecosystem. Dredging especially in the mouth area of the flad can have large effects on the water exchange in the flad and therefore the temperatures. This kind of changes can have tragic effects on the flads functioning as a reproduction area for perch and pike as the temperatures plays a huge role for their reproduction.
When we only consider dredging and buildings in the flads, then as much as 59 % of all flads in the Quark are affected by humans. If we consider all the other human activities, this number will go up. One of the main goals in the project is to test restoration methods in flads and do four restorations. During 2019 we have done in total 5 restorations at the coast. These restauration activities done in the project are expected to result in better functioning of the reproduction areas for fish. We are soon going to publish a report about this where we describe the restorations in detail and give suggestions for future restorations for flads in the Quark.
Summary of the restorations done in the Kvarken Flada project:
1. Restoration of the threshold of the flad, Halsskärsgraven, Ratu, Västerbotten
We have restored Swedens very first flad treshold. Flad threshold is the part of the flad that limits water exchange between the flad and the sea. This flad was dredged at the threshold which resulted in that the whole flad at times become dry when the water escaped to the sea at low water. We filled the dredged part and left a nice creek for the fish so that they can migrate to the flad for spawning.
2. Changing a culvert upstream from a flad, Ratu, Västerbotten
Some of the fish that migrate to the restored flada mentioned earlier (Halsskärsgraven), do in fact migrate further upstream to a lake and spawn there. Between the flad and the lake there were an old culvert that at times made it difficult for the fish to get through. We changed it to a half culvert that works better for the fish migration.
3. Restoration of a creek, Djupsundsbäcken, Holmsund, Västerbotten.
Fish migrate from the sea up to a nearby glolake through a creek named Djupsundsbäcken.
This creek was straightened, and all the rocks were taken away from the creek which made it almost impossible for the fish to get up to the spawning grounds because some parts of the creek were dry. We restorated the creek by making it curvy again and putting back the rocks that higher the water level in the creek.
4. Change of a culvert at a flad treshold, Verkviksfladan, Österbotten.
The old culvert was too high up and made it hard for fish to migrate through from the sea to the flad for spawning. The old culvert was changed to a new one that was placed 50 cm lower than the old one.
5. Restoration of a creek between a flad and a glo, Bredgrund, Österbotten
The creek between the flad and the glo was muddy and overgrown by reed so that the fish had hard time to migrate from the flad to the glo for spawning and back to the sea. The creek was restored with help of small rocks (50-100 mm) that were placed to the creek to prevent the vegetation to overgrow.