The signal crayfish is native to North America west of the Rocky Mountains, including the Canadian province of British Columbia, and the U.S. states of Washington, Oregon, and Idaho.[6] It was introduced to California in 1912 into the San Lorenzo River watershed and from there rapidly spread throughout the state.[7] The only native crayfish remaining in California (aside from Pacifastacus leniusculus klamathensis, a subspecies of signal crayfish believed to be native to the Klamath River in Northern California) is the Shasta crayfish, of Shasta County, California (Pacifastacus fortis), where efforts are being made to create a barrier to signal crayfish invasion.[8] Within North America, it has also been introduced to Nevada, and the populations in Utah may be the result of introductions.[6] It has also been found in Alaska, specifically Kodiak Island, in the Buskin River and Buskin Lake. It is listed as a species of least concern on the IUCN Red List.[1]
From 1907, crayfish plague, an infectious disease caused by the water mould Aphanomyces astaci, damaged stocks of the native European crayfish Astacus astacus. Since the signal crayfish occupied a similar ecological niche in its native range, it was imported in the 1960s to Sweden and Finland to allow recreational and commercial crayfish capture.[3] At the time, the signal crayfish was not recognized as a carrier of the crayfish plague.[3] All American species carry the infection, but it is only lethal to individuals that are already stressed; to European species, the infection is rapidly fatal.[9]The signal crayfish is now the most widespread alien crayfish in Europe, occurring in 25 countries, from Finland to Great Britain and from Spain to Greece.[3][10] It was first introduced to Great Britain in 1976,[11][12] and is now widespread across the British mainland as far north as the Moray Firth. It has also been observed on the Isle of Man, but not in Ireland,[9] the last European country to have no alien crayfish.
In both Sweden and Finland (where crayfish are eaten), the catch of signal crayfish exceeds that of A. astacus (European/noble crayfish). The former is sold at roughly half the price compared to the latter.[13]
In Europe, the signal crayfish is included since 2016 in the list of Invasive Alien Species of Union concern (the Union list).[14] This implies that this species cannot be imported, bred, transported, commercialized, or intentionally released into the environment in the whole of the European Union.[15] The signal crayfish is often considered a nuisance species amongst anglers in Europe.[16]
Crayfish are freshwater crustaceans belonging to the clade Astacidea, which also contains lobsters. In some locations, they are also known as baybugs, crabfish, crawfish, crawdaddies, crawdads, freshwater lobsters, mountain lobsters, mudbugs, rock lobsters, signal crawfish, or yabbies. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some species are found in brooks and streams, where fresh water is running, while others thrive in swamps, ditches, and paddy fields. Most crayfish cannot tolerate polluted water, although some species, such as Procambarus clarkii, are hardier. Crayfish feed on animals and plants, either living or decomposing, and detritus.[1]
The name "crayfish" comes from the Old French word escrevisse (Modern French Ãcrevisse).[2][3] The word has been modified to "crayfish" by association with "fish" (folk etymology).[2] The largely American variant "crawfish" is similarly derived.[2]
Some kinds of crayfish are known locally as lobsters,[4] crawdads,[5] mudbugs,[5] and yabbies. In the Eastern United States, "crayfish" is more common in the north, while "crawdad" is heard more in central and southwestern regions, and "crawfish" farther south, although considerable overlaps exist.[6]
The body of a decapod crustacean, such as a crab, lobster, or prawn (shrimp), is made up of twenty body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess one pair of appendages, although in various groups, these may be reduced or missing. On average, crayfish grow to 17.5 cm (6.9 in) in length. Walking legs have a small claw at the end.[8]
Four extant (living) families of crayfish are described, three in the Northern Hemisphere and one in the Southern Hemisphere. The Southern Hemisphere (Gondwana-distributed) family Parastacidae, with 14 extant genera and two extinct genera, live(d) in South America, Madagascar, and Australasia. They are distinguished by the absence of the first pair of pleopods.[12] Of the other three Northern Hemisphere families (grouped in the superfamily Astacoidea), the four genera of the family Astacidae live in western Eurasia and western North America, the 15 genera of the family Cambaridae live in eastern North America, and the single genus of Cambaroididae live in eastern Asia.[10]
The greatest diversity of crayfish species is found in southeastern North America, with over 330 species in 15 genera, all in the family Cambaridae. A further genus of astacid crayfish is found in the Pacific Northwest and the headwaters of some rivers east of the Continental Divide. Many crayfish are also found in lowland areas where the water is abundant in calcium, and oxygen rises from underground springs.[13]
In 1983, Louisiana designated the crayfish, or crawfish as they are commonly called, as its official state crustacean.[14] Louisiana produces 100 million pounds (45 million kilograms) of crawfish per year with the red swamp and white river crawfish being the main species harvested.[15] Crawfish are a part of Cajun culture dating back hundreds of years.[16] A variety of cottage industries have developed as a result of commercialized crawfish iconography. Their products include crawfish attached to wooden plaques, T-shirts with crawfish logos, and crawfish pendants, earrings, and necklaces made of gold or silver.[17]
Many of the better-known Australian crayfish are of the genus Cherax, and include the common yabby (C. destructor), western yabby (C. preissii), and red-claw crayfish (C. quadricarinatus).[20]
In Australia, New Zealand, and South Africa,[22] the term "crayfish" or "cray" generally refers to a saltwater spiny lobster, of the genus Jasus that is indigenous to much of southern Oceania,[23] while the freshwater species are usually called yabbies or kÅura, from the indigenous Australian and MÄori names for the animal, respectively, or by other names specific to each species. Exceptions include western rock lobster (of the Palinuridae family) found on the west coast of Australia (it is a spiny lobster, but not of Jasus); the Tasmanian giant freshwater crayfish (from the Parastacidae family and therefore a true crayfish) found only in Tasmania; and the Murray crayfish found along Australia's Murray River.[citation needed]
In Singapore, the term crayfish typically refers to Thenus orientalis, a seawater crustacean from the slipper lobster family.[24][25][26] True crayfish are not native to Singapore, but are commonly found as pets, or as an invasive species (Cherax quadricarinatus) in the many water catchment areas, and are alternatively known as freshwater lobsters.[27]
In England and Ireland, the terms crayfish or crawfish commonly refer to the European spiny lobster, a saltwater species found in much of the East Atlantic and Mediterranean.[28] The only true crayfish species native to the British Isles is the endangered white clawed crayfish.[29][30]
Fossil records of crayfish older than 30 million years are rare, but fossilised burrows have been found from strata as old as the late Palaeozoic or early Mesozoic.[31][32] The oldest records of the Parastacidae are in Australia, and are 115 million years old[33] and the crayfish Palaeocambarus and Cricoidoscelosus from the Yixian Formation of China are likely around 120 million years old, making them both one of, if not, the oldest known crayfish to date.[34]
Crayfish are susceptible to infections such as crayfish plague and to environmental stressors including acidification. In Europe, they are particularly threatened by crayfish plague, which is caused by the North American water mold Aphanomyces astaci. This water mold was transmitted to Europe when North American species of crayfish were introduced.[35] Species of the genus Astacus are particularly susceptible to infection, allowing the plague-coevolved signal crayfish (native to western North America) to invade parts of Europe.[36]
In several countries, particularly in Europe, native species of crayfish are under threat by imported species, particularly the signal crayfish (Pacifastacus leniusculus).[38] [39] Crayfish are also considered an invasive predatory species, endangering native European species such as the Italian agile frog.
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