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Australian endangered species: Victorian burrowing crayfish

Burrowing crayfish are a particular challenge to survey and to conserve because they live underground, and their ability to disperse is extremely limited. Sometimes this means that impacts on their habitat…

What’s threatening the Mallacoota burrowing crayfish? Point the finger at grazing, forestry, and fishing. Jason Coughran

Burrowing crayfish are a particular challenge to survey and to conserve because they live underground, and their ability to disperse is extremely limited. Sometimes this means that impacts on their habitat go unnoticed and once affected, their populations are unlikely to recover quickly.

This series has discussed these challenges before when discussing burrowing crayfish in Western Australia and in Tasmania. The two Victorian species of burrowing crayfish that are critically endangered are the Warragul Burrowing Crayfish (Engaeus sternalis) and the Mallacoota Burrowing Crayfish (Engaeus mallacoota).

Both of these species are found in Gippsland, but one of them is a dark, glossy creature that prefers sandy soil in a remote bay near Mallacoota, while the other is a ghostly white or pale blue fuzzy specimen found in clay riverbanks in farmland near Warragul.

The site best known for the Warragul Burrowing Crayfish has been identified as Australia’s most diverse crayfish habitat because it supports four different burrowing crayfish species and at least two (possibly three) different species of spiny crayfish (Morey and Hollis 1997). I have visited this site on Labertouche Creek and it is one of the most unassuming biodiversity hotspots imaginable: a paddock that looks like any other in this part of Gippsland except for the fence that keeps the cows away from part of the river bank.

Part of the charm of burrowing crayfish is their cryptic habit — because they spend most of their time underground, most people are unaware that they are even there. Usually, Engaeus crayfish leave muddy chimneys at the entrance to their burrows which allow the careful observer to register their presence. Unfortunately, the Warragul Burrowing Crayfish often build tunnels that do not connect to the surface. This means that finding them may mean damaging their habitat by digging up a section of the river bank.

A ghost of a crayfish: the Warragul burrowing crayfish. Beverly Van Pragh

Status

The Mallacoota Burrowing Crayfish (Engaeus mallacoota) is critically endangered and is officially known from a single location in the Croajingolong National Park. However, in the last two years surveys funded by the Bushfire Royal commission have expanded the range of the species slightly. Tarmo Raadik of Arthur Rylah Institute said the number of burrows indicate that the crayfish may be locally abundant, but their limited distribution still creates a risk for the long term.

Unfortunately, the sandy shifting soils they prefer and the deep burrows they dig make these animals very difficult to collect. Counting burrows is not sufficient evidence as other (non-endangered) burrowing species overlap with their distribution, so we need better ways of collecting these little diggers.

The Warragul Burrowing Crayfish (Engaeus sternalis) is also critically endangered and until recently was known from one location on Labertouche Creek. However, the Baw Baw Shire Council did a biodiversity assessment two years ago which expanded the range of the species. Warragul Burrowing Crays have been found in the townships of Warragul and Drouin by biologist Beverly Van Praagh. She also discovered that their burrows do come to the surface and have a small chimney, but only at certain times of year.

In general, for both species, we know virtually nothing about their ecology, population dynamics or habitat requirements.

Threats

Burrowing crayfish are particularly vulnerable to local environmental disturbance. Fire, drought or large sediment pulses can drastically affect populations, especially when their distribution is as limited as in these two cases.

Even though the Mallacoota Burrowing Crayfish is found in a national park, its range includes grazing land which means their burrows can be trampled by cattle. Timber harvesting in the adjacent state forest can impact vegetation and water quality in the streams that support these crayfish. Recreational fishing is still allowed in the national park, which can pose a risk if fishers mistake these crayfish as “yabbies” and use them as bait.

The Warragul Burrowing Crayfish has a different set of issues as its environment has been subject to 100 years of grazing which has caused streamside erosion and a loss of native vegetation. Gold mining may have had a large impact, and the introduction of trout creates the threat of predation if they venture into the creeks. Given its proximity to town, it is likely that its habitat has been also destroyed by the development of infrastructure such as roads.

Strategy

There are action plans in place for both the Mallacoota Burrowing Crayfish and the Warragul Burrowing Crayfish. Both plans call for more research and surveys due to the lack of information about these species.

One of the challenges is how to conduct surveys when traditional methods (digging up burrows) are destructive and time consuming. Pitfall traps have been used to collect Warragul Burrowing Crayfish in the past. More recently, the Arthur Rylah Institute had a 10% capture rate of Mallacoota Burrowing Crayfish using specially designed burrow tube traps. In future it may be possible to use eDNA (environmental DNA) to determine what species is in a burrow just by sampling the mud at the entrance.

Education is essential for the conservation of burrowing crayfish, because we can’t take appropriate actions unless we know that these gorgeous little creatures are digging in the soil under our feet.

The community education program for the Warragul Burrowing Crayfish began in 1995 with a brochure and some fencing to protect their habitat. It has recently been expanded significantly with information signs near a giant burrowing crayfish installed on the Two Towns Trail between Warragul and Drouin. According to Greg Hollis of the Baw Baw Shire Council, further plans are underway for protecting crayfish habitat.

Some towns have giant bananas, others have giant burrowing crayfish. Greg Hollis

Conclusion

We have already come a long way in recognising and implementing conservation plans for burrowing crayfish. When I dug up my first terrestrial crayfish 20 years ago very few people knew about these engaging crustaceans. My experience in sharing information about burrowing crayfish is always positive: everyone who is lucky enough to meet one of these little guys is charmed by them.

With careful management of our rivers and wetlands we should be able to maintain these populations into the future. Their cryptic habits have a benefit – they can usually avoid predation and survive all but the most severe floods and fires without significant intervention. But we still need to manage their habitats, protect native vegetation and keep the creeks and rivers clean.

And if you get a chance, visit the Two Towns Walk in Warragul and Drouin and keep your eye out for small holes in the mud, knowing that they may lead to the elaborately branched underground world of the burrowing crayfish, a world about which we know virtually nothing.

The Conversation is running a series on Australian endangered species. See it here.

Join the conversation

9 Comments sorted by

  1. Ben Marshall
    Ben Marshall is a Friend of The Conversation.

    Writer

    Is there another species or outlier existing in the west Gippsland region? We had a property two kilometres out of Mirboo North just off Berry's Creek Road, and I was bemused to find burrowing crayfish considerable distances (hundreds of metres) from dams, creeks or obvious water sources. We also found them in the Tarra Bulga national park.

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    1. Susan Lawler

      Head of Department, Department of Environmental Management & Ecology at La Trobe University

      In reply to Ben Marshall

      I've just had a look and there are no less than seven species of burrowing crayfish around Mirboo and Tarra Bulga N. P. The burrows that do not connect to any water source are an amazing feature of the genus Engaeus: some species fill their burrows with clay and catch rainwater, making them the most terrestrial crayfish in the world.

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    2. Ben Marshall
      Ben Marshall is a Friend of The Conversation.

      Writer

      In reply to Susan Lawler

      The first time we saw them (I'm from South Australia and my wife is from New Zealand) we were a/ pleased to find out what was making these muddy burrows and b/ totally bemused to see a creature we totally associated with water on dry land. In the end, I found them quite cute. On reflection, perhaps their association with water remains via the moist soil they prefer, and staying within areas rich in spring activity, as there were on our property and surrounding hilly areas. Nature, eh?

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    3. John Michael Wardell

      logged in via Facebook

      In reply to Ben Marshall

      We bought a property near Thorpdale over 15 years ago with a creek running through it and several springs and the land close to the creek has numerous burrow tubes which we were advised by the vendor had fresh water crayfish which tasted delicious, after taking control of the land we had DSE do a survey and found they were "Narracan Blue" which are highly endangered! Needless to say, we have never tasted them. We have since fenced off the area under a "Bush Tender" trial which was a great scheme.

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  2. Max JUST DEFIANCE Cook

    REALPolitik Outlaw Journalist

    "Bemusing" but one word for my observations of the Australian government's and other far-right-wing dictatorships of the world, in their refusing to accept that climate changes threatening the globe's ecological balance are manmade.

    To me, it's blatantly obvious the Australian LNP, illegitimate government, the least intelligent I've seen in 40 years watching "politics" here, ignore the facts on anthropocentric climate change because they know full-well that their masters in the planet's upper…

    Read more
  3. Diane Crowther

    Senior Scientist, Arthur Rylah Institute for Environmental Research

    Fantastic to see a well rounded article on the elusive burrowing crayfish! Further information on the development and use of the burrowing crayfish tube trap in the Gippsland region is detailed in a report by Bryant, Crowther and Papas (2012). The tube trap has been used in various projects since this research to capture numerous Engaeus species. These include FFG threatened species such as the Lilly Pilly burrowing crayfish (Engaeus australis) and the Dandenong burrowing crayfish (Engaeus urostrictus). The 2012 report can be found via the following link:
    http://www.depi.vic.gov.au/environment-and-wildlife/arthur-rylah-institute/research-themes/fire-ecology-and-recovery/natural-values-2009-fire-recovery-program-ari-reports

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    1. Alastair Richardson

      Honorary Research Associate, School of Zoology at University of Tasmania

      In reply to Diane Crowther

      Thanks for the link, Diane. As I get older and the joints get creakier I'm very keen to find alternatives to excavating crayfish burrows. Quite apart from the more important objective of minimising habitat damage.

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    2. Diane Crowther

      Senior Scientist, Arthur Rylah Institute for Environmental Research

      In reply to Alastair Richardson

      You are welcome Alastair. The traps are a great non-destructive sampling method and certainly save damaging habitat and injuring ageing body parts! The best use of the traps is in spring in damp to wet conditions. Not only does this timing coincide with the presumed mating season of most burrowing crayfish but it also means active burrows are obvious and can be clearly targeted. The traps are very easy to deploy and retrieve so it means you can very effectively cover a large area. Good luck with your continuing great work on burrowing crayfish.

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  4. Dianna Arthur

    Environmentalist

    "everyone who is lucky enough to meet one of these little guys is charmed by them:

    Absolutely.

    I regularly see the muddy chimneys rising in the aftermath of a good downpour here in the Dandenongs. My little critters are a reddish brown in colour, utterly feisty and my favourite crustaceans, that I don't eat.

    After the end of the drought in Victoria, I was delighted to find their muddy towers again. I don't think they are endangered here - but have no real proof apart from personal observation. I can see how disrupting the water table anywhere by any means is/would be a threat.

    Would suggest the burrowing crayfish a terrific emblem for action against fracking.

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