Atlantic sturgeon from Göta River found in Norway
In mid-June, 95 Atlantic sturgeon were released into the Göta River in western Sweden. Now 22 fish have been identified.
- The sturgeon that was found in August in Langesund, Norway, has travelled the furthest, says Johan Höjesjö, professor of ecological zoology.
The last time an animal was reintroduced in Sweden, after being extinct for a long time, was in 1922 when beavers were replanted in Jämtland. This time it is the Atlantic sturgeon, which has been present in the Göta River for 6,000 years but which became extinct about 100 years ago due to heavy fishing and poor water quality.
The enthusiastic initiator of the replanting programme is biologist Dan Calderon of Environmental Technology West. He had the idea back in 2012. At the time, it was known that Atlantic sturgeon used to swim in the Göta River, but the question was whether they also spawned here.
"During an inventory of the collections at the Gothenburg Museum of Natural History, several specimens of juvenile Atlantic sturgeon were found, preserved in alcohol and labelled with the date and place of capture. This provided clear evidence that sturgeon had spawned in the river at the end of the 19th century," says Johan Höjesjö.
Swimming long distances
After various twists and turns, the idea of replanting sturgeon really took off last year. One reason was another enthusiast: Linnéa Jägrud at the Swedish Sport Fishing and Fisheries Conservation Association. A collaboration was initiated between Environmental Technology in the West, the Gothenburg Museum of Natural History, the University of Gothenburg, the Swedish Sport Fishing and Fish Conservation Association and the Swedish University of Agricultural Sciences (SLU). At the beginning of 2024, the county administrative board gave the go-ahead for replanting, says Johan Höjesjö.
"The 95 sturgeon we have now released were bred in a tank in Germany, where they have been replanting for some twenty years. At the time of release, the sturgeons were 10 months old and about half a metre long. The sites we selected with the help of our German colleagues are outside Lilla Edet, Göta and Kungälv.
To keep track of the sturgeons, they are tagged with acoustic telemetry, for which SLU has been responsible. This means that the fish are fitted with transmitters that send out unique sound signals. Receivers are placed at various locations along the Göta River, the Nordre River and in estuaries outside, which pick up the signals when a fish comes near and the researchers can thus follow the movement pattern of each individual, explains Johan Höjesjö.
"However, the 22 fish we have now managed to find have been manually localised from a boat. 16 fish have been found between Lilla Edet and Kungälv, two between Kungälv and Nordre älv and another two between Kungälv and Göta älv, one of which was found just outside Göteborgsoperan. One fish was found dead off Marstrand. On 28 August, a sturgeon was caught in Langesund and released - in just over a month, it had swum an impressive distance all the way to Norway!"
An ecological engineer
The sturgeon is a truly ancient fish that has been around for over 200 million years. It also looks quite ancient: its elongated body lacks scales and instead has five rows of bony plates. The nose is long and flat and the mouth, which can be folded out, is on the underside.
"When searching for food, the fish is also aided by four smooth, rounded beard teeth that help it sense the bottom environment. Young fish thrive in freshwater, but when they are big enough to cope with the salinity, they migrate to the sea. At 12-15 years of age, they return to freshwater to spawn."
But what happens to these fish that have grown up in pools, do they return to the Göta River? ‘Yes, that's one of the questions the researchers are interested in,’ explains Johan Höjesjö.
"Another question is how old the sturgeon should be to survive optimally. Perhaps we should have released them when they were younger, but then they might have been eaten instead? Another important question is how the introduced sturgeon will affect the bottom fauna and fish community in the Göta River. The Atlantic sturgeon is something of an ecological engineer, buoying and oxygenating the bottom. How the environment will be affected is something three biology students will do a degree project on."
At the end of September, the receivers that have collected information about the jammers will be emptied. An analysis is then expected to be completed by mid-October,’ explains Johan Höjesjö.
"The plan now is to start up our own cultivation facilities. ‘We will continue to collect sturgeon in Germany, but we will receive younger fish so that we can continue to breed them ourselves before releasing them."
The plan is to eventually release around a thousand sturgeon a year into the river.
"However, establishing a stable population will take at least 50 years. So this is a long-term endeavour," says Johan Höjesjö.
Text: Eva Lundgren
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.
