Crayfish plague

As long as there are signal crayfish in a watercourse, it is very difficult to reintroduce noble crayfish. However, if all crayfish disappear from a waterbody, the fungal spores cannot survive. A few weeks after the last crayfish has disappeared, the water is again free from plague infection.

Spread

The spread of crayfish plague has increased dramatically in recent years due to illegal releases of signal crayfish. Between 1994 and 2007, nearly a thousand lakes, rivers, and watercourses were affected by crayfish plague.

Unfortunately, crayfish plague spreads quickly, and the number of infected water areas continues to increase. Further information about crayfish plague-infected areas can be obtained from the respective county administrative boards.

 
Crayfish plague-infected signal crayfish with visible plague spots on the tail. The signal crayfish comes from an illegal release in a lake in Värmland. Even though a signal crayfish is infected, the plague attack is not always visible to the naked eye.

Spread via illegal release of signal crayfish

It is primarily the extensive illegal releases of signal crayfish that have contributed to the rapid spread of the plague in recent years. Signal crayfish are always carriers of the disease, but rarely get sick. Crayfish plague can also spread through wet fishing gear, other equipment, bait fish, or spores in water.

Noble crayfish more valuable

The areas in Sweden that have completely avoided being affected by crayfish plague are now only found in Norrbotten County. In addition to the loss of biodiversity, significant economic value is lost since noble crayfish have more than twice the sales value of signal crayfish. The noble crayfish is currently listed as critically endangered on the Swedish Red List of Threatened Species, 2020.

Signal crayfish can also get sick

Signal crayfish have naturally higher resistance to crayfish plague than noble crayfish, but they can also get sick if stressed by other factors, such as pollution, poor access to food, high densities, or unfavorable water temperatures.

It is forbidden to release or move crayfish

It is prohibited to release or move signal crayfish without permission from the county administrative board. Permits are only granted where the species is already legally established. There are also strict regulations for handling the species. For example, the entire Gotland has been a protected area for noble crayfish since 2007.

Dry equipment and boats

To avoid spreading crayfish plague, you should not move fishing gear, boats, and other equipment between different waters without first disinfecting them. This can be easily done by allowing the equipment to dry completely, including boats, traps, and boots.

Only use bait fish from the same water you are fishing in. Alternatively, freeze the bait for a day, as this will kill the crayfish plague.