Threats/Control Methods - Regional
The current range of Water Rats is thought to be similar to that occupied prior to European settlement. However, human modification of waterways has undoubtedly reduced habitats in some areas of Australia. Land clearing and stock grazing along water ways erodes river banks and destroys nesting sites, while increasing river salinity kills the saline sensitive plants than form an important part of the Water Rat's diet.
Threats/Control Methods - Local
Water bodies in urban areas are less resilient against periods of drought or extreme weather events, causing a build-up of toxins and dangerous algae levels, which may impact the health of this species and the species it relies on for food. Free-roaming domestic pets are especially threatening to young Water Rats.
It is important that our waterways remain free from pollution, to encourage a healthy and wide range of species for the Water Rat's diet. Joining in with a local Waterwatch activity can help improve water quality. At home, it is important avoid chemicals, pet faeces or garden waste going down the stormwater drain. Keep gutters clean and call the Canberra Connect helpline (02) 6207 9777 for specific chemical waste disposal information. Reducing the impact of domestic pets on this species can be achieved by keeping dogs on leash while walking near waterways and by providing a stimulating indoor environment or outdoor enclosure for cats, rather than allowing them to roam freely. These actions will also protect a suite of other native bird, reptile, frog and mammal species.
Water Rat, Golden Water Rat, Beaver Rat and over 50 Aboriginal names
The Water Rat is a large amphibious rodent. It has strong partially webbed hind feet that act as paddles when swimming, and dense, soft water-repellent fur. It is about the size of a rabbit, with adults growing between 23 and 37cm (excluding the tail). The body colouring is variable, from slate grey to almost black on its upper body and white to orange on the lower body. Despite this variation in body colouring, all Water Rats have a long (between 24 and 34cm) thick tail with a white tip at the end. The Water Rat has small, round, dark eyes and long silvery whiskers.
The False Water Rat (Xeromys meroides) is smaller and lighter coloured with a lack of webbed hind feet. Its range is limited to specific areas on the coasts of QLD and NT.
The species is located in Australia, New Guinea, and a number of adjacent islands. The Water Rat is common in eastern Australia, occurs west to the Kimberleys along the northern coast and west to Eyre Peninsula on the southern coast. Its range is restricted inland. Small populations occur in south-western Western Australia and on a number of offshore islands, including Tasmania.
Country of Origin
Spotlighting, trapping and daytime sitings. This species can be readily sited at dusk. The LSCCES identified the species by spotlighting.
Conservation (Pet/Pest) Status - National
Secure, not listed under the EPBC Act 1999.
Conservation (Pet/Pest) Status - Regional
One individual was sited at the Acton Peninsula during LSCC surveys, though it is also known to occur along Sullivans Creek on the ANU campus and was observed during frog surveys conducted as part of the LSCCES.
Associated vegetation community
Found in permanent fresh or inland salt water, such as lakes, swamps, farm dams and creeks. They can sometimes occur in marine environments. The species is common in urban environments with water bodies.
The species can withstand a wide range of variability in environmental conditions from sub alpine streams to tropical coastal habitats. It is negatively affected by heat stress in hot, dry climates, which is why it is less common in inland Australia.
Water Rats breed throughout the year but peak-breeding season occurs from September through January. Nests are built at the end of burrows in banks of lakes, streams, and other bodies of water. The number of litters that a female produces each year is dependent on availability of food and water. In a good year, females can produce up to five litters, each with 3-4 young, with as many as seven young recorded. Young Water Rats are weaned at four weeks and remain with the mother for an additional four weeks. Social factors also affect the timing of breeding and age at first breeding.
The Water Rat is not entirely nocturnal, but its peak time of activity is at sunset. At this time they can be seen repeatedly duck-diving for food, surfacing briefly for air. They are territorial and inhabit a range of 2-10 hectares with variation being influenced by habitat. If populations are dense, males will fight and usually damage their tails.
The Water Rat mainly feeds on large aquatic insects, fish, mussels and crustaceans. Among insects, water beetles (Coleoptera) and water bugs (Hemiptera) are of primary importance, and nymphs of damselflies and dragonflies (Odonata) can be seasonally important food sources. They also eat frogs, lizards, small mammals, fresh carrion and birds. Plants also supplement their diet, particularly in winter.
Birds of prey and Cats (Felis catus ) predate adult Water Rats, while snakes and large fish prey upon young rats.
References - (reader suitability of references, P=Primary teachers, S=Secondary students, T=Tertiary students and researchers)
Books:Straham, R. 1983. The Australian Museum Complete Book of Australian Mammals. The National Photographic Index of Australian Wildlife. Angus and Robertson Publishers. Sydney. P, S, T
Journals:Olsen, P. 1995. Water-rat Hydromys chrysogaster. Pp. 628-629 in The Mammals of Australia (R. Strahan, ed.). Reed Books. Chatswood NSW. S, T
Online Publications:ACT Government. 2006. Information Sheet: Stormwater Pollution from Residential Areas. Environment ACT. [online]. Available at: http://www.environment.act.gov.au/__data/assets/pdf_file/13168/Stormwater_Pollution_from_Residential_Areas.pdf P, S, T
CSIRO. 2004. Water for a Healthy Country: Hydromys chrysogaster. [online]. Available at: http://www.anbg.gov.au/cpbr/WfHC/Hydromys-chrysogaster/ S, T
Department of Environment and Conservation. 2006. Water Rat. Government of Western Australia. [online]. Available at: http://www.naturebase.net/component/option,com_docman/task,doc_details/Itemid,1288/gid,147/ P, S, T
Tidemann, C., Roscoe, T. and Mitchell, B. 2006. Mammals of the Lower Sullivans Creek Catchment, Canberra ACT. Prepared for the Life in the Suburbs project using data from the Lower Sullivans Creek Catchment Ecological Survey (LSCCES). Australian National University. Canberra. [online]. Available at: http://www.lifeinthesuburbs.com.au/category.php?id=65 S, T
Rockdale City Council. Unwanted Visitors. Produced as part of the Council's Rodent Control Program. Rockdale NSW.http://www.rockdale.nsw.gov.au/pdf/a_rat_brochure.pdf P, S, T
Researcher: Hedda Ranson-Elliott and Naomi Hogan