Signal cancer
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Signal cancer ( Pacifastacus leniusculus ) |
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| Pacifastacus leniusculus | ||||||||||||
| ( Dana , 1852) |
The signal crayfish ( Pacifastacus leniusculus ) is the crayfish very similar originating from North America crayfish , which as well as in Europe neozoon occurs.
description
At 12 cm (females) or 16 cm (males), the signal crayfish is slightly smaller than the noble crayfish (the Latin species name leniusculus means "the little gentle one"). The males are up to 200 g larger and heavier than the approximately 80 g females, they also have larger claws. The animals are around 7 to 10 years old.
The carapace of the signal crayfish is smooth and, unlike that of the noble crayfish, has no thorns behind the neck furrow. The Rostrumränder appear approximately parallel in plan as that of the crayfish. The basic color is brown with a tendency towards olive. The top of the scissors is marked with a turquoise-white spot on the joint of the scissor finger, which gave the signal crab its German name. However, this signal spot can also be absent or only be very indistinct. The underside of the scissors is conspicuously red and serves as a warning color when lifting the scissors .
nutrition
Like most crayfish, the signal crayfish is an omnivore , which includes aquatic insect larvae, mollusks and living and dead plant material, e.g. B. Eats leaves . Young animals tend to be much more predatory than larger individuals, whose stomach contents are often dominated by detritus and plant fragments. In addition, the food depends on what is available in the respective body of water. At high population densities, signal crabs can exert considerable predatory pressure on preferred prey species and eliminate them from a body of water. The foraging usually takes place at night, but can also be extended to the daytime if the cancer feels safe. This is especially true when there is a lack of food.
Multiplication
Mating takes place once a year in autumn from October to November, preferably after a drop in temperature. The eggs and later larvae are carried and looked after by the female. From May, but usually not until June / July, the young crabs become independent. They are sexually mature after about two years.
habitat
The signal crab prefers to live in cool rivers (around 15 ° C) with a slightly alkaline pH value (7–8) and a higher water hardness (10–25 ° dGH). Since it can withstand higher temperatures in contrast to the noble crayfish, it can also be found in still waters such as smaller lakes .
The signal crab creates its own habitat in the water: Usually caves are dug under stones or between roots. However, the animals are not necessarily tied to a cave; sometimes a new cave is occupied even after a forage-hunt.
The signal crab can also be kept in a sufficiently large aquarium. Keeping it in a garden pond can cause the signal crab to migrate. Because it can walk long distances (up to 2 km) over land to reach another body of water. In addition, it is also important to observe national legislation, as keeping it is not permitted everywhere (for example in Switzerland).
The fishing and nature conservation laws of most European countries meanwhile expressly prohibit the stocking of signal crayfish in open waters.
distribution
The signal crab originally comes from the area in western Canada and the western USA west of the Rocky Mountains in North America . Since 1860, the population of the native noble crayfish, which used to be found everywhere in the European lowlands, has been massively decimated by the crab plague . In order to revive the crab fishery, the signal crab was introduced as a neozoon from 1960, first by Sweden, and later by other European countries . Signal cancer is now established in almost all European countries. In Central Europe it is currently the most common non-native crayfish species after the crayfish .
Displacement of native species
The signal cancer is resistant to the cancer plague, also from North America, and brought a new, highly virulent strain of the pathogen to Europe. In addition, the signal crayfish is more aggressive than native crayfish and, in the case of stone crayfish and jackdaw crabs , also grows significantly larger and produces more offspring. It is thus superior to the native species in direct competition and completely displaces them from their habitats.
In contrast to the crayfish , the signal crayfish also actively penetrates into the summer-cool upper reaches of the water, which until now have often offered safe refuge for the local crayfish. Expansive signal crabs are therefore one of the greatest threats to the remaining populations of the three crayfish native to Central Europe ( noble crayfish , stone crayfish and jackdaw crayfish ).
Signal crayfish has been added to the list of invasive alien species of Union concern .
literature
- Chucholl, C. & Dehus, P. (2011): Crayfish in Baden-Württemberg . Fisheries Research Center Baden-Württemberg (FFS), Langenargen, 92 pages
- Hans Gonella: Guide to crabs, crabs and shrimp in freshwater aquariums , bede-Verlag 1999, ISBN 3-931-792-87-0
- Johannes Hager: Edelkrebse Leopold Stocker Verlag , Graz 1996, ISBN 3-7020-0751-2
- Reinhard Pekny & Manfred Pöckl: Red List of Lower Austria crayfish and freshwater shrimp , Amt d. Lower Austria state government department of nature conservation, ISBN 3-901542-17-5
- Chris Lukhaup & Reinhard Pekny: Crayfish from all over the world Dähne Verlag 2008, ISBN 978-3-935175-40-1 .
- Uwe Werner: Pacifastacus leniusculus. In: Claus Schaefer, Torsten Schröer (Hrsg.): The large lexicon of aquaristics. Eugen Ulmer, Stuttgart 2004, ISBN 3-8001-7497-9 , p. 736.
Web links
- Online identification key for crayfish in Baden-Württemberg
- Description of the signal crab on Anglertreff.org
- Pacifastacus leniusculus inthe IUCN 2013 Red List of Threatened Species . Posted by: Schuster, GA, Taylor, CA & Cordeiro, J, 2010. Retrieved September 29, 2013.
Individual evidence
- ↑ Chucholl, C. & Blank, S. & Brinker, A. (2017): The protection of the crayfish - A guide . Ministry for Rural Areas and Consumer Protection Baden-Württemberg, Stuttgart, 84 pages
- ↑ Chucholl, C. & Blank, S. & Brinker, A. (2017): The protection of the crayfish - A guide . Ministry for Rural Areas and Consumer Protection Baden-Württemberg, Stuttgart, 84 pages
- ↑ List of Invasive Alien Species of Union Concern (PDF) accessed on July 15, 2016