Hairy marron  (Cherax tenuimanus)

The hairy marron is classified as Critically Endangered (CR) on the IUCN Red List (1).

One of the largest freshwater crayfish in the world, this hairy-shelled species has jet black pinchers and a paler olive-green to brown body. The hairy marron's (Cherax tenuimanus) underside is brown and females have areas of red colouration on the underside and some splashes of purple (3). The head and internal organs of all crayfish are protected by the carapace and the six segments of the abdomen are individually encased with a flexible membrane between them to allow movement. Crayfish have a pair of large pinchers at the front end, followed by four pairs of walking legs and then four pairs of small swimming legs called swimmerets. These swimmerets are covered with fine hairs to which the female attaches her eggs. A central tail flap is surrounded by four other flaps that are used to move the crayfish rapidly through the water, as well as curling up to form a brood chamber in females. There are two eyes on the end of eyestalks, but the senses of touch and taste are far more important. These are perceived using a pair of large feelers (or antennae) and a pair of small, fine, centrally located feelers (or antennules) (3).

The marron was split into two distinct species in 2002, when it was realised that some individuals were hairy (Cherax tenuimanus) and others were smooth (now known asthe smooth marron, Cherax cainii). The newly-named hairy marron is endemic to the Margaret River in southwest Western Australia (4).

The hairy marron is found in the permanent freshwater tributaries of forested high-rainfall areas (5).

Hairy marrons require the correct light levels, water temperature and diet for breeding. Mating at the start of spring, the male passes a spermatophore between the female’s final pair of walking legs. The female uses this to fertilise her eggs, incubating between 200 and 300 of them on her swimmerets for 12 to 16 weeks. When carrying eggs, females are said to be ‘berried’ due to the appearance of a bunch of berries on each swimmeret. The eggs hatch into pre-juveniles in early summer and become mature adults within a year (2).

Hairy marrons do not burrow to escape drought like other freshwater crustaceans and are comfortable on land for short periods. They are omnivorous, feeding on detritus and other small organisms found on the detritus (2).

Having previously thought that the smooth marron (Cherax cainii) and the hairy marron (Cherax tenuimanus) were the same species, people translocated the smooth marron in large numbers into Margaret River. It is now known to out-compete the hairy marron in regions where the river habitat is degraded due to loss of vegetation or poor water flow (5). The hairy marron has suffered an 80 to 90 percent reduction in numbers due to the human-induced invasion of the smooth marron (4). Other introduced species are also thought to be contributing to the hairy marron’s decline (5).

The Western Australia Department of Conservation and Land Management is working together with the Department of Fisheries and the public to develop and implement a recovery plan for the hairy marron. In addition, the importation of non-native crayfish species is banned in Australia to prevent the spread of the crayfish plague fungus that has been responsible for the decline of several European crayfish species (2).

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on the hairy marron:

• The Government of Western Australia, Department of Fisheries website:
  http://www.fish.wa.gov.au/aqua/broc/aqwa/marron/index.html