Signal crayfish
Encyclopedia
The signal crayfish, Pacifastacus leniusculus, is a North America
n species of crayfish
. It was introduced to Europe in the 1960s to supplement the Scandinavia
n Astacus astacus
fisheries, which were being damaged by crayfish plague
, but the imports turned out to be a carrier of that disease. The signal crayfish is now an invasive species, ousting native species across Europe and Japan.
The life cycle
of the signal crayfish is typical for the family Astacidae
. Around 200–400 eggs
are laid after mating in the autumn, and are carried under the female's tail until they are ready to hatch the following spring. The eggs hatch into juveniles
, which pass through three moults
before leaving their mother. Sexual maturity
is reached after two to three years, and the life span
can be up to 20 years.
The signal crayfish is an omnivore
, with most of its dietary intake being detritus
.
west of the Rocky Mountains
, including the Canadian province
of British Columbia
, and the U.S. state
s of Washington, Oregon
, and Idaho
. It was introduced to California
in 1912 into the San Lorenzo River
watershed and from there rapidly spread throughout the state. The only native crayfish remaining in California is the Shasta crayfish
(Pacifastacus fortis), where efforts are being made to create barrier to Signal crayfish invasion. Within North America, it has also been introduced to Nevada
, and the populations in Utah
may be the results of introductions. It is listed as a species of Least Concern
on the IUCN Red List
.
, an infectious disease caused by the water mould
Aphanomyces astaci, damaged stocks of the native Europe
an 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. It was not realised at the time that the signal crayfish was a carrier
of the crayfish plague. 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.
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
. It was first introduced to Great Britain in 1976, 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
.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
n species of crayfish
Crayfish
Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
. It was introduced to Europe in the 1960s to supplement the Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
n Astacus astacus
Astacus astacus
Astacus astacus, the European crayfish, noble crayfish or broad-fingered crayfish, is the most common species of crayfish in Europe, and a traditional foodstuff. Like other crayfish, Astacus astacus is restricted to fresh water, living only in unpolluted streams, rivers and lakes...
fisheries, which were being damaged by crayfish plague
Crayfish plague
Crayfish plague, Aphanomyces astaci, is a water mould that infects crayfish, most notably the European Astacus which dies within a few weeks of being infected...
, but the imports turned out to be a carrier of that disease. The signal crayfish is now an invasive species, ousting native species across Europe and Japan.
Description and ecology
Members of this species are typically 6–9 cm (2.4–3.5 ) long, although sizes up to 16 centimetre are possible. They are bluish-brown to reddish-brown in colour with robust, large, smooth claws. They have a white to pale blue-green patch near the claw hinge, like the white flags that signalmen used for directing trains—hence the name.The life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
of the signal crayfish is typical for the family Astacidae
Astacidae
The family Astacidae comprises the freshwater crayfish native to Europe and western North America. It is made up of three genera. Pacifastacus is found on the Pacific coast of the United States and British Columbia and includes the signal crayfish and the Shasta crayfish...
. Around 200–400 eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are laid after mating in the autumn, and are carried under the female's tail until they are ready to hatch the following spring. The eggs hatch into juveniles
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
, which pass through three moults
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
before leaving their mother. Sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
is reached after two to three years, and the life span
Longevity
The word "longevity" is sometimes used as a synonym for "life expectancy" in demography or known as "long life", especially when it concerns someone or something lasting longer than expected ....
can be up to 20 years.
The signal crayfish is an omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
, with most of its dietary intake being detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
.
Native range
The signal crayfish is native to North AmericaNorth America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
west of the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
, including the Canadian province
Provinces and territories of Canada
The provinces and territories of Canada combine to make up the world's second-largest country by area. There are ten provinces and three territories...
of British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, and the U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
s of Washington, Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
, and Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
. It was introduced to California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
in 1912 into the San Lorenzo River
San Lorenzo River
The San Lorenzo River drains a large watershed in Santa Cruz County, California. The headwaters originate in the Santa Cruz Mountains at an elevation of , and the river flows through the San Lorenzo Valley before emptying into the Pacific Ocean at Monterey Bay...
watershed and from there rapidly spread throughout the state. The only native crayfish remaining in California is the Shasta crayfish
Shasta crayfish
Pacifastacus fortis is an endangered crayfish species endemic to Shasta County, California, where it is found only in isolated spots on the Pit River and Fall River Mills....
(Pacifastacus fortis), where efforts are being made to create barrier to Signal crayfish invasion. Within North America, it has also been introduced to Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
, and the populations in Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
may be the results of introductions. It is listed as a species of Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
on the IUCN Red List
IUCN Red List
The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...
.
Introduction into Europe
From 1907, crayfish plagueCrayfish plague
Crayfish plague, Aphanomyces astaci, is a water mould that infects crayfish, most notably the European Astacus which dies within a few weeks of being infected...
, an infectious disease caused by the water mould
Water mould
Oömycota or oömycetes form a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms . They are filamentous, microscopic, absorptive organisms that reproduce both sexually and asexually...
Aphanomyces astaci, damaged stocks of the native Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
an crayfish Astacus astacus
Astacus astacus
Astacus astacus, the European crayfish, noble crayfish or broad-fingered crayfish, is the most common species of crayfish in Europe, and a traditional foodstuff. Like other crayfish, Astacus astacus is restricted to fresh water, living only in unpolluted streams, rivers and lakes...
. Since the signal crayfish occupied a similar ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
in its native range, it was imported in the 1960s to Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
and Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
to allow recreational and commercial crayfish capture. It was not realised at the time that the signal crayfish was a carrier
Disease carrier
Disease carrier could refer to:* Asymptomatic carrier, a person or organism infected with an infectious disease agent, but displaying no symptoms* Genetic carrier, a person or organism that has inherited a genetic trait or mutation, but displaying no symptoms...
of the crayfish plague. 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.
The signal crayfish is now the most widespread alien crayfish in Europe, occurring in 25 countries, from Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
to Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
and from Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
to Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
. It was first introduced to Great Britain in 1976, and is now widespread across the British mainland as far north as the Moray Firth
Moray Firth
The Moray Firth is a roughly triangular inlet of the North Sea, north and east of Inverness, which is in the Highland council area of north of Scotland...
. It has also been observed on the Isle of Man
Isle of Man
The Isle of Man , otherwise known simply as Mann , is a self-governing British Crown Dependency, located in the Irish Sea between the islands of Great Britain and Ireland, within the British Isles. The head of state is Queen Elizabeth II, who holds the title of Lord of Mann. The Lord of Mann is...
, but not in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
.