Sturgeon makes a comeback in Swedish waters
It's been over a hundred years since the Atlantic sturgeon swam in the river Göta Älv in western Sweden. Now, the County Administrative Board has given permission to reintroduce the mythical fish into its former waters.
After several years of preparatory work, a hundred young sturgeons will be released in Göta Älv this summer in the small town Lilla Edet upstream from Gothenburg. The Return of the Sturgeon Project is a collaboration between the Swedish University of Agricultural Sciences, Gothenburg Museum of Natural History, the Swedish Anglers' Association, and the University of Gothenburg. Together, they have thoroughly investigated the conditions for a reintroduction of the species.
"This is a unique event. It 's not common for Sweden to actively reintroduce a regionally extinct species. It's so exciting, and I'm really looking forward to the day when we can look at the river and say 'there are Atlantic sturgeons swimming below the surface here'," says Linnéa Jägrud, project manager at the Swedish Anglers' Association.
Overfishing and environmental pollution
Until the end of the 19th century, there were spawning populations of Atlantic sturgeon in Göta Älv. But the species died out, mainly due to heavy fishing and deteriorating water quality. Today, the water quality is much better and the conditions are just right for the species to spawn in the river.
"Together with German researchers, we have inventoried the main channel of Göta Älv and found three suitable spawning grounds: Kungälv, Göta, and Lilla Edet. According to the Germans, there are very good conditions for the sturgeon to thrive there," says Johan Höjesjö, Professor of Ecological Zoology at the University of Gothenburg.
The Atlantic sturgeon can grow to over four metres long and weigh over 350 kilograms. Despite its size, it feeds mainly on bottom-dwelling animals and depends on finding food in the sediments. During the upcoming year, three students from the Department of Biology and Environmental Science will do their degree projects on the food web in Göta Älv and how it could be affected by the return of the sturgeon. They will study both the bottom fauna and the fish community to get an idea of the potential food supply for the sturgeon.
"It will be exciting to see how the sturgeons affect life in the river. Although Göta Älv is the most fish species rich freshwater river in Sweden, it's surprisingly little studied," says Johan Höjesjö.
Sturgeons from Germany
In collaboration with sturgeon experts from the German Leibniz-Institute for Freshwater Ecology and Inland Fisheries in Berlin, the project has ensured access to fry as well as genetically valuable individuals. The German experts are the best in Europe when it comes to the ecology of the Atlantic sturgeon and have long experience of working on the re-establishment of the species.
The next step will be to bring in a group of young fish, around half a metre long, for a test release. A dozen individuals will be tagged and monitored to ensure that the strategic project is working in practice. In May, the rest of the fish will be transported to Sweden.
Monitoring will provide knowledge about fish movement
Like salmon, the Atlantic sturgeon spend their first years in freshwater. When they are big enough to cope with the salinity, they migrate out into the sea in search of food. Then, they return to spawn in freshwater.
An important part of the re-establishment work is monitoring. This is done by researchers at the Swedish University of Agricultural Sciences, having previously tagged fish with acoustic telemetry. By tagging the sturgeon and placing telemetry equipment at several locations in the river and along the coast, the researchers can monitor and analyse the movement patterns of the sturgeon. This will provide valuable insights to where in the river the sturgeon feed and what the most viable habitat conditions are.
The technology is crucial for identifying and protecting spawning areas, and the data collected will help the project plan future restoration work to further streamline the re-establishment process, which will also benefit other species.
"The Atlantic sturgeon can become an ambassador species for Gothenburg and the entire Göta Älv. By bringing back this ancient fish, we show that the water quality is good and that many fish and other animals can thrive here," says Johan Höjesjö.
Text: Karl-Johan Nylén
Background: Formerly found along large parts of the Swedish coast and in many rivers. Extirpated sometime during the 20th century.
Age: Can be 130 years old. Propagate and spawn in rivers. Live as young in the rivers until they develop resistance to salt water. Then wanders into the seas and avoids only when they are sexually mature at 12 to 17 years of age.
Size: Old individuals can be over four meters long and weigh over 300 kilograms.
Food: Eats worms, crustaceans, molluscs, fish and plant parts.