Smooth marron - Cherax cainii

Originally ranging from Harvey to Denmark, however due to translocation for recreational fishing it is now distributed from the Hutt River to Esperance – including in many major water supply and farm dams. It has also been introduced into South Australia and Victoria, where it is considered a pest, as well as overseas.  While its range has increased north and east in south-western Australia, is has also declined from inland parts of its former range mostly due to secondary salinisation of major rivers (similar to other crayfish and fish).

Occupies permanent waters of rivers, lakes, reservoirs and farm dams.

It prefers areas with complex habitat, particularly large woody debris – which provides both shelter from avian and introduced fish predation, but also food sources; with marron foraging on both the woody material and also any attached algae, plant, bacteria or invertebrates. Marron are detritivore/omnivore, though they are also an opportunistic carnivore (e.g. choosing to eat meat when they can).

They can tolerate elevated salinity, however, growth is impaired at around 6-8 g/L and they are rarely found to be self-maintaining at salinities higher than those levels. The species is intolerant of low dissolved oxygen (less than 2 mg/L) and high temperatures (greater than 29 C). Its distribution in reservoirs can be restricted due to low dissolved oxygen in deeper habitats.  It has also been shown to withstand low pH; living in acidified mines lakes as low as pH 4 – however growth is expected to be retarded, both as the species will need to expend energy to regulate in these conditions, and as diet options are reduced (algae and invertebrate communities are depauperate at low pH). Naturally marron are more commonly found around neutral pH.

Peak spawning usually occurs between July and October, with eggs (up to ~1200) held and protected under the tails of females where they hatch with juveniles subsequently released from November/December.

The species is fast growing but the rates vary among populations.  Size at sexual maturity has been shown to vary among populations (between ~30-65 mm OCL) but is typically achieved between 2-3 years old.

The species in not listed, however, many populations are under pressure from declining range and abundance due to salinisation, habitat degradation, and localised depletion from legal and illegal fishing.

Smooth marron are carefully managed to ensure the future viability of stocks. This includes a very limited length of the licensed recreational fish season (~4 weeks in summer) and restrictions on gear type, bag and size limits that are underpinned by ongoing monitoring of stocks and research into their biology.