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.
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.
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.