After the turn of the millennium, the amount of signal crayfish increased markedly in Lake Vättern and commercial fishermen increased their catch sharply, but too sharply, according to the researchers.

- 90 percent of what is fished in Lake Vättern professionally is signal cancer, says Patrik Bohman.

More sustainable in Hjälmaren

In Hjälmaren, crayfish also increased significantly, but fishing there is judged to be at a more sustainable level.

- We believe that it is due to a more balanced fishing there, says Patrik Bohman.

But the professional fisherman Rolf Gustavsson from Hjo thinks that the comparison with Hjälmaren is unfair.

- In Lake Vättern, almost all crayfish fishing is on public water.

In Hjälmaren, crayfish fishing is on private water and then they control it themselves, so it is probably not really possible to compare, says Rolf Gustavsson.

The number of crayfish is also increasing in Lake Vänern, but these are more modest catches.

In Lake Mälaren, commercial fishermen basically no longer catch crayfish.

In the 60s, the Freshwater Laboratory planted signal crayfish.

They coped better with the plague, but carried the virus and killed large parts of the remaining populations of Swedish crayfish.

In the clip, the cancer researcher explains more.

This is how crayfish fishing has developed over the past 25 years in Lake Vättern (red line), Hjälmaren (blue line) and Lake Vänern (green line).