As the largest freshwater invertebrate in the world, with records of specimens reaching more than five kilograms in weight and over 80 cm in length, the Tasmanian Giant Freshwater Lobster sometimes known as a crayfish is found only in the rivers of northern Tasmania, although habitat disturbance combined with a long history of fishing has contributed to its decline.

The spiny Tasmanian Giant Freshwater Lobster varies in colour from blue to brown, as well being jet black. Today, the average weight of 2-3 kilograms is considered large. Also referred to by biologists as the ‘freshwater Thylacine’, due to not only the fact that it was is heading towards extinction, but it is also the largest animal and predator in its freshwater habitat, as was the Thylacine on Tasmania’s land.

Protected Status
The Tasmanian Giant Freshwater Lobster is currently protected, originally listed in 1995 as ‘vulnerable’ and placed on the Tasmanian Threatened Species Protection Act and the Commonwealth Endangered Species Protection Act. From 1st January, 1998, it was declared a ‘protected fish’ under the Inland Fisheries Act. With a maximum fine for taking lobsters of $10,000, it is now illegal and a finable offence to catch or disturb the animal in any way. Disturbance include kill, injure, catch, damage, destroy or collect the animal, either deliberately or accidentally.
 

Continuing habitat disturbance, including the removal of stream vegetation, bank erosion, desnagging, channelisation, siltation, nutrification and chemical pollution continues to occur at every level from the small private landholder to large scale commercial forestry. Increased ‘roading’ has led to a significant increase in fishing pressure and access to previously unexploited populations. The clearing of streamside vegetation, extensive modification of stream channels, access by stock and influx of chemicals and nutrients have also contributed to the decline of lobster populations.

In addition, they grow extremely slowly, only at a pace of 5-10 mm per year for some adults, with it reaching maturity at a late age of 9 years in males and 14 years in females. Reproduction in females occurs only every two years, making Astacopsis gouldi very vulnerable to disturbance of the environment or over fishing by humans.

Range
The range of the Tasmanian Giant Freshwater Lobster is found only in rivers of northern Tasmania that flow into Bass Strait with the exception of the Tamar catchment. It is also found in the Arthur River catchment, which flows into the West Coast, occurring in river systems below 400m, and being most numerous in streams below 200m. Interestingly, their range coincided with that of the blackfish Gadopsis marmoratus.

Activity, Diet and Habitat
The Tasmanian Giant Freshwater Lobster are slow growing, slow to colonise new areas and have a low reproductive rate. With a diet of mainly decaying wood and leaves, fish, rotting flesh and detritus are also eaten. While little is known of their dispersal patterns individuals have been recorded moving 500m in 24 hours, with movements over land also being recorded. They have been recorded as most active during early autumn and summer when water temperatures are higher.

By nature, the Tasmanian Giant Freshwater Lobster is shy and secretive. With the ideal habitat including intact stream catchment of several stream sizes, including rivulets and small headwaters. These should flow and meander through a relatively undisturbed well vegetated catchment containing snags, pools and undercut, but not eroding, banks. The water temperature should seldom exceed 18°C, have a high oxygen content and be clear of sediment.
 

Juvenile lobsters have been located in shallow faster flowing areas known as riffle zones. It is suspected they migrate into smaller stream zones including semi-permanent creeks. It is in these areas that they are safer from many predators such as larger fish (blackfish, trout) and platypus, which struggle to swim in the very shallow sections. The juveniles find cover amongst the cobble rocks and woody debris and remain in this area until large enough to move into the deeper areas known as runs. Runs are deeper flowing straight sections of a catchment. Many sub adult (<100mm CPL) have been located in these areas. It is suspected that these sub adults are not large enough to enter the domain of the adult lobsters, the deeper pools.

Adults take refuge in still, deep pools, which are sheltered and well shaded beneath submerged and decaying timber and can live in larger numbers (up to 20 individuals) in one large pool. Although sometimes aggressive, lobsters appear to tolerate one another in these pools. It is estimated that lobsters may live beyond 40 years.
 

Measuring a juvenile.

Further information available on the
Tasmania's Giant Fresh Water Lobster from the Inland Fisheries Service.

There is a distribution map of the giant freshwater lobster on the Parks & Wildlife site.