The invasive killer shrimp is now found in at least 18 places around Lake Vättern, according to the county administration’s comprehensive inventory that was carried out this summer.
– It is very sad for biological diversity, says Friederike Ermold at the Vätternvårdsförbundet.
The killer shrimp, or greater predatory merle as the crustacean is actually called, is an invasive species that can cause great damage to the ecosystem.
After the species was discovered for the first time in Sweden last winter, outside Vadstena, all the county administrations around Lake Vättern carried out an extensive inventory along the shoreline during the early summer.
The spread is fast
It turns out that larger predatory marten have spread to at least 18 places along the east coast, Visingsö and up to Bankeryd on the west side.
– It is very sad, but also expected. Once the species was identified in Lake Vättern, we knew it was only a matter of time before it would spread, and it is happening quickly, says Friederike Ermold.
The inventory of surrounding lakes and waterways, such as the Göta canal, shows that they have so far managed. It also indicates that the killer shrimp probably came to the lake via a sport fishing boat transported there.
General crayfish fishing worries
According to the crustacean’s DNA profile, which Polish researchers have studied, the population now found in Lake Vättern comes from Western Europe, where the species is established in several watercourses.
For the invasive species to gain a foothold in new waters, an uncleaned hull or a bit of debris left on the bottom of the boat is enough. And with a lot of activity in Vättern right now, when the general crayfish fishery is going on, the experts are very concerned about further spread.
– The water is run. What we are afraid of now is that it will spread to other watercourses such as Lake Vänern and the Motala stream, so it is very important that when you move your stuff from Lake Vättern you really drain all the water and wash and dry the equipment properly, says Friedrike Ermold at the Vätternvårdsförbundet.