Tasmanian giant freshwater crayfish
Encyclopedia
The Tasmanian giant freshwater crayfish (Astacopsis gouldi) is the largest freshwater
invertebrate
in the world. The species is only found in Tasmania
(an Australian island), and is listed as a vulnerable species due to habitat loss and over fishing. It is also severely threatened by siltation and de-snagging of streams as decaying wood forms the favourite part of its diet. It is not known if the animals are nourished by the wood, the bacteria
, algae
or invertebrates living in the rotting logs. They also eat leaves, fish and other meat, including other freshwater
invertebrate
s.
Individuals of over 5 kilograms (11 lb) in weight and over 80 centimetres (31.5 in) long have been known in the past, but now, even individuals over 2 kilograms (4.4 lb) are rare. The species is only found in Tasmanian rivers flowing north into the Bass Strait
(with the exception of the Tamar) below 400 metres (1,312.3 ft) above sea level, and is listed as an endangered species
on the IUCN Red List
. The specific epithet gouldi commemorates the Australian naturalist
John Gould
.
A. gouldi is very long-lived, surviving for up to 40 years. Their main predators are humans, platypus
, river blackfish
and rakali.
of several females. Hatchlings are a mere 6 mm long, and mature extremely slowly, living for up to 40 years. Reproductive maturity occurs at around nine years in males and 14 years in females, with females breeding just once every two years. Mating occurs in autumn and the eggs, attached to the female’s swimming legs during development, hatch the following summer, remaining attached to the swimming legs as hatchlings for another month. Such a long reproductive process means that females spend much of their life with their young attached to their legs – a good strategy as fully grown adults have no natural predators. However, fishing of adult crayfish by humans results in the removal of not only the adults but all their young as well.
The giant freshwater crayfish is omnivorous, eating primarily rotting wood and animal flesh, as well as leaves and insects that fall into the water. Juveniles tend to hide in shallow water where they are less at risk from their large predators including fish and platypuses. Adults hide under submerged logs in deep pools where they appear to tolerate each other, despite being aggressive elsewhere.
The giant freshwater crayfish was previously found in all rivers that flow into the Bass Strait, which runs between Tasmania and the Australian mainland. Today, however, the distribution is patchy and limited to less disturbed areas.
The decline of giant freshwater crayfish numbers following intense resulted in a fishing ban in January 1998, although an ongoing commitment is needed in order for the crayfish to recover from its endangered status. Population surveys and behavioural research are being undertaken in order to be able to provide better habitat protection and improved management of riverbank vegetation.
This species was listed as "vulnerable" under Australia
n law in 1995, and it is now illegal to catch A. gouldi without a permit, carrying a maximum fine of A$
10,000.
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
in the world. The species is only found in Tasmania
Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...
(an Australian island), and is listed as a vulnerable species due to habitat loss and over fishing. It is also severely threatened by siltation and de-snagging of streams as decaying wood forms the favourite part of its diet. It is not known if the animals are nourished by the wood, the bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
or invertebrates living in the rotting logs. They also eat leaves, fish and other meat, including other freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s.
Individuals of over 5 kilograms (11 lb) in weight and over 80 centimetres (31.5 in) long have been known in the past, but now, even individuals over 2 kilograms (4.4 lb) are rare. The species is only found in Tasmanian rivers flowing north into the Bass Strait
Bass Strait
Bass Strait is a sea strait separating Tasmania from the south of the Australian mainland, specifically the state of Victoria.-Extent:The International Hydrographic Organization defines the limits of the Bass Strait as follows:...
(with the exception of the Tamar) below 400 metres (1,312.3 ft) above sea level, and is listed as an endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
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...
. The specific epithet gouldi commemorates the Australian naturalist
Natural history
Natural history is the scientific research of plants or animals, leaning more towards observational rather than experimental methods of study, and encompasses more research published in magazines than in academic journals. Grouped among the natural sciences, natural history is the systematic study...
John Gould
John Gould
John Gould was an English ornithologist and bird artist. The Gould League in Australia was named after him. His identification of the birds now nicknamed "Darwin's finches" played a role in the inception of Darwin's theory of evolution by natural selection...
.
A. gouldi is very long-lived, surviving for up to 40 years. Their main predators are humans, platypus
Platypus
The platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...
, river blackfish
River Blackfish
The river blackfish, is an Australian native freshwater fish of the Murray-Darling river system, found from southern Queensland through to central Victoria. It is also found in some eastern and southern flowing coastal rivers...
and rakali.
Biology
Astacopsis gouldi is territorial. Males maintain a haremHarem
Harem refers to the sphere of women in what is usually a polygynous household and their enclosed quarters which are forbidden to men...
of several females. Hatchlings are a mere 6 mm long, and mature extremely slowly, living for up to 40 years. Reproductive maturity occurs at around nine years in males and 14 years in females, with females breeding just once every two years. Mating occurs in autumn and the eggs, attached to the female’s swimming legs during development, hatch the following summer, remaining attached to the swimming legs as hatchlings for another month. Such a long reproductive process means that females spend much of their life with their young attached to their legs – a good strategy as fully grown adults have no natural predators. However, fishing of adult crayfish by humans results in the removal of not only the adults but all their young as well.
The giant freshwater crayfish is omnivorous, eating primarily rotting wood and animal flesh, as well as leaves and insects that fall into the water. Juveniles tend to hide in shallow water where they are less at risk from their large predators including fish and platypuses. Adults hide under submerged logs in deep pools where they appear to tolerate each other, despite being aggressive elsewhere.
Habitat and range
These crustaceans inhabit dark, slow-moving rivers and streams with high water quality and little suspended sediment, as well as still, deep pools with logs and overhanging banks to shelter beneath. The water needs to be below 18°C with high oxygen content.The giant freshwater crayfish was previously found in all rivers that flow into the Bass Strait, which runs between Tasmania and the Australian mainland. Today, however, the distribution is patchy and limited to less disturbed areas.
Threats and Conservation
The major threat to this species has been over-fishing, since these crayfish are a popular food dish, but this has not been sustainable due to extremely slow maturation and infrequent breeding. Habitat loss is also a threat, as a result of increasing agricultural expansion, forestry operations and changes in water quality. In-stream barriers have reduced the dispersal potential of the crayfish and erosion following agricultural expansion has caused silty water, which is less favourable for the giant freshwater crayfish.The decline of giant freshwater crayfish numbers following intense resulted in a fishing ban in January 1998, although an ongoing commitment is needed in order for the crayfish to recover from its endangered status. Population surveys and behavioural research are being undertaken in order to be able to provide better habitat protection and improved management of riverbank vegetation.
This species was listed as "vulnerable" under Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n law in 1995, and it is now illegal to catch A. gouldi without a permit, carrying a maximum fine of A$
Australian dollar
The Australian dollar is the currency of the Commonwealth of Australia, including Christmas Island, Cocos Islands, and Norfolk Island, as well as the independent Pacific Island states of Kiribati, Nauru and Tuvalu...
10,000.