The Tasmanian giant freshwater crayfish (Astacopsis gouldi), also called Tasmanian giant freshwater lobster, is the largest freshwater invertebrate and the largest freshwater crayfish species in the world. The species is only found in the rivers below above sea level in northern Tasmania, an island-state of Australia. It is listed as an endangered species on the IUCN Red List due to overfishing and habitat degradation, and it has been prohibited to catch the crayfish since 1998.
The diet of the freshwater crayfish varies with age, but predominantly consists of decaying wood, leaves and their associated microbes. They may also eat small fish, insects, rotting animal flesh and other detritus when available. A. gouldi is very long-lived, surviving for up to 60 years. It has previously been reported to attain weights of up to and measure over long; however, in recent years the majority of larger specimens are . When full-grown the species has no natural predators due to its large size, while smaller individuals can be prey of platypus, river blackfish and rakali. In Tasmanian Aboriginal language (palawa kani) the giant freshwater lobster is referred to as lutaralipina. Previously, it has been common to use 'tayatea' as the Aboriginal name for A. gouldi. Astacopsis gouldi was first formally described in 1936 by Ellen Clark, a naturalist specialising in Australia's crustaceans. Prior to Clark's revision in 1936, all three of Tasmania's large stream-dwelling crayfish of the genus Astacopsis were collectively known as Astacopsis franklinii in honour of the polar explorer and Governor of Van Diemen's Land Sir John Franklin.
thumb|left|The [[watercolor painting|watercolour sketch]]Astacopsis franklinii now refers only to the smaller southern species, while the medium-sized western species is known as Astacopsis tricornis and Astacopis gouldi refers exclusively to the giant northern crayfish. It is a common misconception that A. gouldi is named after the convict artist William Buelow Gould. WB Gould's "Sketchbook of fishes" produced at the Macquarie Harbour penal settlement contains an image of the large western Tasmanian freshwater crayfish A. tricornis not A. gouldi. Males can be identified by their larger pincers compared to females.
Distribution and habitat
thumb|right|[[Flowerdale River, Meunna, North West Tasmania. A waterway ecosystem where Astacopsis gouldi is likely to occur]]
Distribution
A. gouldi inhabit rivers and streams at elevations of approximately above sea level, with upper limits of . Approximately 18% of the waterways in which the species habitat is predicted to occur are protected in a formal reserve.
Formerly, the species was distributed from the Arthur River in the west and eastwards across northern Tasmania, where it was found in all rivers flowing into Bass Strait, except for those of the Tamar catchment. The species has been introduced into the North Esk (St Patricks River) and the Derwent catchments where populations have become established. However, the striking nature of the species makes it a potential tourism drawcard.
Threats and conservation
The principal causes for the population declines of the Tasmanian giant freshwater crayfish have been previous overfishing, continued illegal fishing and habitat disturbance by agriculture, forestry and urban activities. Experts estimate there are less than 100,000 remaining in the wild. New developments of fire roads and double track trails can consequentially allow illegal fishers to access previously unexploited populations.
Notable events
In 1994, a large spill from a holding dam at a pyrethrum extraction plant caused a major kill in the Hogarth Rivulet and the main channel of the Great Forester River. Reports from locals and fisheries officers suggested that there was little life left in much of the main channel, and the incident is believed to have severely harmed any populations that were in the waterways at the time of the spill.
The 2016 Tasmanian floods, which killed 3 people, raised concerns about the future for the Tasmanian giant freshwater crayfish after up to 100 carcasses were found washed up along the banks of the Leven River on a property in North West Tasmania, likely caused by the high water flows during the flood. Previous population surveys in the area had revealed already low numbers. There are further concerns that the floods displaced snags from waterways which are a vital part of the habitat for the species.
Identified important locations
The 2006–2010 Giant Freshwater Lobster Recovery Plan highlighted several catchments (or parts of) which had been identified to contain good habitat quality and good crayfish populations and should be considered for conservation efforts. Some areas require renewed evaluation since habitat quality may have changed since surveys were conducted. North-eastern Tasmanian rivers lacked sufficient data to fully determine all areas of importance.