All cancers are invasive

Crayfish: Bans against invasive cancers

Almost every child in this country knows imported prawns or lobsters, but very few of us have ever seen a Swiss crayfish. No wonder: On the one hand, these animals are nocturnal and, on the other hand, the populations of the three native types of cancer have declined sharply. The noble crayfish is one of the endangered animal species in Switzerland, the stone crayfish and the jackdaw crayfish are even considered to be endangered.

There are several reasons for this: The crabs are affected by the high level of pollution in the water, and they suffer from the loss of habitat in the heavily built-up bodies of water. They are also bothered by the competition from four relatives from outside the site who were deliberately settled as edible crabs or released by private aquarium owners. And finally they are threatened by cancer plague.

Disastrous disease

According to the International Union for Conservation of Nature (IUCN), the cancerous pathogen - an egg fungus related to brown algae - is one of the 100 most dangerous invasive species in the world. Cancer plague is practically always fatal in European crabs. It originated in North America and has been spread in European waters by American crayfish since the 19th century, resulting in the extinction of tens of thousands of crayfish populations. However, fishermen, boat owners and divers can also spread the pathogen's spores if they do not disinfect boots, suits or boat hulls with a suitable agent when they move from one body of water to another.

Four uninvited guests

The threat posed by the four immigrant, non-native cancers varies in size. The most harmless is Immigrant No. 1, the Galician crab from Eastern Europe. He lives in lakes and ponds. As a result, it is in some places in competition with the noble cancer, the largest native species. But in contrast to the American types of cancer, the Galician cancer also falls victim to the cancer plague and therefore does not carry the disease further.

Stressed or weakened American crayfish can also perish from crayfish plague, but many specimens are infected with the crayfish plague without becoming sick themselves. This has fatal consequences for the native crabs. The penetration of a single disease carrier is enough to exterminate an entire population within a short period of time.

The signal cancer - it owes its name to bluish spots on the scissor joints - is considered to be particularly invasive. Immigrant No. 2 is very happy to hike and also dares to venture into smaller side waters. It endangers the last remaining black and jackdaw crabs in Switzerland.

Immigrant No. 3, the red marsh crayfish, is popular with aquarium owners because of its attractive color. He likes to dig caves, which can lead to the destabilization of dams and embankments. And it is extremely undemanding and can also find its way in damp meadows, temporary bodies of water and swamps. When it is dry, he withdraws to his den.

Finally, immigrant number 4, the Kamberkrebs, prefers muddy subsoil and, in contrast to the native species, also endures poorer water quality. Its distribution is limited to large rivers and lakes in the Central Plateau.

Native Species Conservation Action Plan

The FOEN gave priority to the protection of indigenous crayfish species and launched a national crayfish action plan as early as 2006. Its aim is to curb the spread of invasive species and is ideally integrated into the national strategies on biodiversity and on invasive alien species that the Federal Council adopted in 2012 and 2016.

In order to bundle forces, a total of 30 hard-core and jackdaw crab populations that are particularly worthy of protection were defined in the action plan after consultation with the cantons. These so-called gene pool locations could also serve as a source for possible resettlements in the future. For example, if a population were to be wiped out due to temporary water pollution or to promote the spread of the species. Crayfish are an important part of a natural body of water. They eat plant matter and leaves, ensure that dead aquatic animals disappear quickly, and their young serve as rich food for fish.

In order to support the cantons in their protection efforts, the FOEN suggested the establishment of a national competence center. The Swiss Crayfish Coordination Office (KFKS), financed by the FOEN, began its work at the Northwestern Switzerland University of Applied Sciences in 2014.