Australasian Science: Australia's authority on science since 1938

Conserving Freshwater Crayfish in Australia

Australia has a rich diversity of freshwater crayfish, but many of our species are at risk.

When Thomas Huxley – Darwin’s “bulldog” and greatest advocate – searched for an animal on which to base his Introduction to Zoology (1880), he naturally settled on the humble crayfish. In his own words, he wanted to show how “the careful study of one of the commonest and insignificant of animals, leads us […] to the widest generalisations and the most difficult problems of zoology”. Unfortunately, in his discussions he completely ignored one of the richest countries in freshwater crayfish – Australia.

Home to 148 of the 600 species recognised globally, Australia is a heavyweight of crustacean diversity. This includes the world’s largest freshwater invertebrate – the Tasmanian giant Astacopsis gouldi, weighing in at a whopping 5 kg – and some of the smallest species measuring barely 1 cm. Not only are Aussie crayfish species numerous and diverse, they are evolutionary relics. They diversified around 150 million years ago – the same time as the global radiation of birds.

Australian crayfish drifted away from their South American and Malagasy cousins during the split of the Gondwanan supercontinent. Isolated on a continent with extremely variable water availability, they slowly evolved to fill a number of niches.

Some crayfish live exclusively in fresh waters, some live in temporary desert springs, while others dig burrows to access the water table. These extensive galleries would often fall under the weight of cattle and horses in the 19th century, so parts of eastern Victoria were renamed “crabhole country”. Problems of land subsidence decreased as crayfish became locally extinct due to damaging farming practices.

The global IUCN assessment recently revealed the dire condition of Australian crayfish – 66 species are threatened with extinction. The proportion of threatened species in some genera is extremely high: more than 80% in the spiny crayfish species (Euastacus spp.), and three out of five burrowing species from Western Australia (Engaewa spp.).

Yet local conservation measures are lagging behind the global recognition of the threatened status of crayfish. Only 11 species are included on the Environment Protection and Biodiversity Conservation Act, leaving dozens of species in urgent need of listing.

Australian species are affected by a wide range of interacting threats. They suffer from the loss of riparian vegetation, invasive species (cane toads and other crayfish), and the deposition of nutrients, mercury and sediments in waterways.

Climate change is an emerging though poorly-understood threat. Most spiny crayfish are endemic to mountain-tops, so their habitats may become unsuitable under climate change. In lowlands, the disappearance of riparian vegetation is likely to deprive crayfish from cool microhabitats. What this means is that crayfish populations are likely to decline further if threats remain unabated.

The good news is that crayfish are well-known invertebrates: there is considerable ecological data, a complete phylogeny, and all species are mapped within their IUCN assessment. Further work in Australia could leverage the international interest triggered by the global assessment as well as help build national capacity. Many university departments focus on fish and crayfish biology, and crayfish enthusiasts are very knowledgeable and passionate. Crayfish are appreciated by the general public, both as pets and as delicious sandwich fillings – the economic value of crayfish farming is estimated at $20 million. Crayfish therefore have the capacity to become flagship species for the conservation of freshwater invertebrates.

Key research and conservation questions will need to be answered to move crayfish conservation forwards. This includes transferring knowledge from well-known to poorly-known species; testing the efficacy of conservation measures (such as revegetation of riparian areas); and developing guidelines on captive breeding and translocation.

The process of listing crayfish under the Environment Protection and Biodiversity Conservation Act also needs to be enhanced – especially for crayfish that live in flowing water, which remain largely underrepresented on the list (three of 11 species). Maintaining up-to-date recovery plans and conservation advice is also a challenge due to the lack of ongoing monitoring.

I am leading a global study on the factors predisposing crayfish to high extinction risk. Part of this is a global study of crayfish vulnerability to climate change. It is my hope that large-scale ecological information will help inform research priorities within Australia, and identify transferable conservation methods from other continents. With this in place Australia may be able to retain its claim to being the world’s crayfish capital.

Lucie Bland is a member of the ARC Centre of Excellence for Environmental Decisions (CEED). She based at The University of Melbourne.