New invasive species discovered in Vättern

The Greater Marlin (Dikerogammarus villosus) originates from the Caspian Sea. With the help of humans, it spread to countries like Poland, Germany, Great Britain and Holland. It is now generally established there.

– Unfortunately, says Ulf Bjelke, a limnologist at the SLU Art Data Bank.

Invasive species

The greater marten is larger and stronger than the Swedish species and is more aggressive, for example, killing more prey than it eats. When predatory merle invade the water, the small animal community changes frequently and many local species are drastically reduced or disappear. It is very unfortunate that this is precisely what was discovered in Vättern and many other complexes.

Discovered through environmental monitoring

– Vättern’s coastal region has rich diversity and high natural values. That’s why we do regular inventories of aquatic insects, crustaceans and molluscs, says Frederik Ermalt, an expert on water issues at Vätternvårdsförbundet, which coordinates the environmental monitoring program for Vättern.

It was during a routine investigation called environmental monitoring that the species was discovered in three complexes on the eastern side of Lake Vattern.

– Friedrich Ermold says the discovery is a good example of the importance of environmental monitoring for early detection of alien species.

It is not clear how this species reached Vattern Lake. One explanation is that it was moved from other waters into the lake with boats or other equipment.

Prevent spread

Eradication of the species is considered impossible. However, this finding gives us an opportunity to prevent the spread from Lake Vattern to other water bodies. We humans are the main propagators of these species – and we can do something about it.

– Make sure your fishing equipment and bath toys are dry and clean before using them in another body of water, says Lina Tomasson, coordinator for invasive alien species at the Norwegian Sea and Water Authority.

To avoid spreading, there are a few things to keep in mind:

• Drain all water from your boat or equipment before moving it.
• Before moving dry equipment such as wetsuits, bath toys, fishing gear, boats and other equipment to fresh water. Allow it to air dry for a couple of days.
• Clean boats and equipment of plant parts, animals and sediment before moving them to new water.

Continuous mapping of species in Östergötland

Since it is not mapped how these species got to Lake Vättern, the Östergötland County Administrative Board plans to list the Motala stream and the Göta canal and some small tributaries. This is to see if there is a more predatory merle that could have made it to Lake Vattern via one of these routes and to prevent the species from spreading further.

– To prevent spread, it is important for the public to have good knowledge about invasive alien species and how they spread. In recent years, we’ve done a lot of information efforts about invasive alien species, why they’re a problem and what you should do if you see them, says Linnea Carlson, aquatic invasive alien species coordinator for the Östergötland County Administrative Board. It is clear that this work must continue.