In the past, it was usual that well over a thousand puffins would perch on the wooden docks in Sandviken. There are many fewer there now. The Puffins have settled instead in Eidsvåg in periods. Perhaps this is because of the pollution in By Fjord.
That large flocks of puffins come regularly to the Nordhordland Bridge, is due to other reasons, however. The pontoons on the bridge provide a good substrate for shell larvae to attach to. At the mussel plant, the pieces of rope or "netting stockings" that hang down into the sea serve the same function. During the course of a year, the larvae grow a 3-4 centimetre-long shell. Then it is party time for the puffins if the plant is not protected from these diving guests. The Nordhordland bridge is a warning that there can be many unwelcome visitors at a mussel plant used for aquaculture, and there are generally several others who come during the course of a year.
Without the help of the fish farming or the bridge, puffins would have to find mussels on stones or another more or less firm substrate in the upper layers of the seawater, preferably in places with a lot of current. The shells live on algae and other small nutrient particles that get filtered from the water. Parts of Oster Fjord have always provided good living conditions. That the salt content in the Fjord is low does not pose any problem. It is more important that there is a good current, making life easier, among other ways, by helping to spread the eggs. One mussel produces 5-10 million eggs per year.
The way that they feed makes mussels vulnerable to poisoning, either from toxic algae or from environmental pollutants in the water. This is a well known problem for people, but seldom for birds. It is not easy to see from a shell if it has been poisoned, but many places in the country, the amount of pollutants in the water is measured in the summer, so that people can avoid being poisoned by mussels.
