The image has been provided as part of the Rakali Community Survey. This new citizen science project is designed to improve knowledge of this elusive native rodent whose current distribution, habitat needs and threats are poorly known. As a top-order predator, rakali may be useful indicators of healthy waterways, and this project will also aim to influence better management of rivers and wetlands in Southwest Australia.
Dr Geoff Barrett, the chief ecologist at DBCA in the Swan Region, gave us a very interesting talk on the Rakali (Hydromys chrysogaster). Rakali is the aboriginal name for the Native Water Rat. It is Australia’s only aquatic placental mammal. It is common throughout the south-west, even in the Perth metropolitan area. It has webbed feet, large whiskers, small ears and strong jaws for crunching marron, gilgies and mussels. It is often mistaken for a rat, even though it is twice as large as a rat. Its tail is not as long as the body and has a distinctive white tip. It has a pale underbelly and a dark grey back. The Rakali has three or four young per year. It is mostly nocturnal and cryptic, so it’s not often seen. It likes well-wooded streams with logs and steep river banks and its presence is an indicator of a healthy river. Each Rakali needs a 400–500m2 territory. Rakali can be found near farm dams but they have to be clean. It can also do well in brackish water. Rakali leave prominent footprints and scats and you can often see its middens of mussel shells. Its favourite food is Carter’s Freshwater Mussel, which is under threat and classified as P5. The Rakali is classified as P4 and they often occur together.
The major threats to the Rakali are water abstraction, decline in rainfall and loss of wetlands. There has been a 30 per cent drop in rainfall in the past few decades and this plus water abstraction has led to 70-80% of the wetlands in the Swan Coastal Plain disappearing. Good populations of Rakali have been found in the Warren River catchment.
Other threats are predation by foxes, cats and dogs. When housing increases, so do the Black Rats and camera footage has shown Black Rats fighting and driving out the Rakali. Marron traps are another cause of deaths in Rakali. Marron traps are illegal in public waters and only the nets with drop sides should be used, as these are a much safer alternative.
Dr Barrett organized a ‘citizen science’ Rakali survey in 2014–15. The World Wide Fund for Nature and Lotterywest gave grants for this and 167 volunteers participated, producing 234 sightings of animals. Most of these were around Perth and the Warren region and other parts of the south-west. There are some Rakali on Barrow Island which forage on the shoreline, though it is puzzling where they get their fresh water on Barrow Island. In previous reports there were a lot of records of Rakali in Helena Valley prior to 1960 but none there in later surveys.
WWF also came up with the idea of a ‘Rakali walk’, which is like a transect, but in a straight line 400m long along watercourses, observing signs along the way. Fifty-four walks were done down as far as Walpole. Half of these had middens, 56% of which contained mussels, 18% crayfish and 18% scats. In another survey of causes of death, it was found that 43% of Rakali were killed in Marron traps, 20% killed by vehicle strikes, 10% drowned and 7% were predated. The Fisheries Dept in Manjimup reports from 2008-2016 showed 39 Oblong Turtles and 12 Rakali were killed in Marron traps. More information can be found on Fisheries’ website.