Giant freshwater crayfish  (Astacopsis gouldi)

This magnificent crayfish is the largest known freshwater invertebrate and has particularly powerful pinchers (2). They range in colour, according to habitat and location, from dull brown to greeny-black, but can have steely blue sides, or be dazzling blue all over (4).

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 (3).

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 (2) (3) (4). The water needs to be below 18 oC with high oxygen content (5).

The giant freshwater crayfish is a mere 6 mm long as a hatchling, and matures extremely slowly, living for up to 40 years (5). Reproductive maturity occurs at around nine years in males and 14 years in females, with females breeding just once every two years (2). 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 (2). However, fishing of adult crayfish by humans results in the removal of not only the adults but all their young as well (3).

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 (5).

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 (5). Habitat loss is also a threat, as a result of increasing agricultural expansion, forestry operations and changes in water quality (3). 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 (4).

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 (3).

For more information see:

Animal Diversity Web (September 2004):
http://animaldiversity.ummz.umich.edu/site/accounts/information/Astacopsis_gouldi.html

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