Rakali research in the Murrumbidgee

Interview with PhD student Emmalie Sanders

Emmalie Sanders is a PhD student with the School of Agricultural, Environmental and Veterinary Science at Charles Sturt University. She has spent the last few years conducting research on rakali (native water rats) in the Murrumbidgee catchment area. We caught up with Emmalie to ask her some questions about these cool little creatures and find out how her research is going.

Describe rakali for those who haven’t had the delight of seeing one:

Rakali are an incredibly charismatic native rodent and one of the few semi-aquatic mammals in the world. They are the largest rodent in Australia and can weigh up to 1.3 kg, but resemble a small otter both in appearance and behaviour. Rakali come in a variety of colours but in NSW are usually brown with a pale yellow belly and the distinctive white tip to their tail. They are an asset to their ecosystem with many benefits including predation of invasive fish and cane toads, and of course the entertainment factor for anyone lucky enough to see them.

Rakali are quite common across eastern Australia and within the Murrumbidgee catchment area. They are not currently considered threatened locally or nationally, however they are susceptible to predation by cats or foxes, drowning in enclosed fishing nets and drought. They are found around most waterbodies including creeks, billabongs, lakes and even dams and irrigation channels with available food sources such as fish and crustaceans. They are generally more abundant in areas with dense low-lying vegetation surrounding the water and emergent logs that provide safe resting areas while foraging. They require stable banks to create burrows or hollow logs to nest in and usually forage in water less than two meters deep. Rapid fluctuations in water level can flood burrows and cause mortality in juveniles; however I am still researching the effects of water quality, turbidity or flow rate on rakali. They have proven relatively hardy to pesticides in the water so long as food sources remain available, but drastic habitat alteration, such as vegetation removal and the lining of channels can lead to population declines.

Emmalie with an adult male rakali at Broome back water on the Yanco Creek, July 2022. Photo credit Zac Rolfe.

This rakali was caught in a cage trap mounted to a floating platform. It was one of four set each night, with an additional six cage traps on land and ten small aluminium traps (Elliott traps) at each site. Traps were set and baited with sardines at sunset and opened again at sunrise. We weighed each rakali in a bag with a spring balance, then measured its body length, head length and width, hind foot length, tail length and length of the white tip. I tagged each with a passive integrated transponder (PIT tag or microchip) so we could identify them it if we got recaptures, then we released it where it was captured. I also collected any scat left behind for looking at their diet. A total of 19 individuals were caught during the PhD study.

What led you to study Rakali in the Murrumbidgee Catchment Area?

I was first introduced to the rakali by my PhD supervisor, Dr Jamie Turner, and quickly became obsessed. They are usually quite abundant, yet so many people do not even know they exist. Looking at their distribution I found there was quite a gap in online records of rakali within the Murrumbidgee catchment area, especially in comparison to areas along the Murray River or around metropolitan areas. I wanted to fill this gap and determine whether they were really absent from much of the area or just severely under-reported.

What questions did you set out to answer in your PhD studies?

I aimed to answer five main questions throughout my studies:

  1. How at risk are rakali in relation to other semi-aquatic mammals?
  2. What is the most effective method to detect rakali?
  3. What habitat resources are important for rakali populations?
  4. How does changing hydrology influence rakali abundance?
  5. What influences rakali activity patterns?
Two rakali caught on camera at Broome along Yanco Creek, July 2023. These were recorded on the riverbank near the water’s edge, attracted to the site by the sardine tin lure.
Rakali eating a carp on Lake Urana. These platforms were used for monitoring. They floated up and down with water levels, had a sardine tin used as a scent lure and a camera set up to record any rakali activity.

What has been the most interesting finding of your study?

Learning how to effectively monitor rakali has been a big part of my study. The effectiveness of motion sensitive camera traps in recording rakali presence was truly surprising. Camera traps have increased in their use over the last 20 years and provide a great alternative to traditional trapping methods. They are non-invasive and can be set for long periods of time. Yet, previous studies using camera traps have had limited success detecting semi-aquatic species, including otters and platypus. It was believed the animals retained a similar body temperature to their surroundings so the camera’s passive infra-red trigger could not distinguish them from the environment.

I tested three different camera positions including a forward-facing camera and a downward-facing camera set along the edge of a waterbody, and a camera overlooking a floating platform deployed in the water. The most effective approach was camera overlooking a floating platform. I captured multiple pictures of rakali swimming about while foraging and using the platform to eat what they caught. I set up even more cameras across the system in 2023 and recorded over 63,000 images of rakali alone, making remote camera traps a great method to observe rakali.

What have you liked the most about studying in the Murrumbidgee area?

I love the variety of habitats in the system. There are so many hidden gems and wetlands that you wouldn’t know about just driving by, so getting to see them, and how they have changed over the years and seasons is truly amazing.

How does Commonwealth water for the environment benefit Rakali?

While rakali are quite resilient they are still tied exclusively to water availability. Rakali don’t breed as prolifically as introduced rodents and have relatively short lifespans, making them susceptible to local extinctions during drought. Maintaining areas of permanent water as drought refuges are extremely important and provide habitat when other water sources are scarce. Rakali have been known to travel multiple kilometres in search of water, but good connectivity of waterways can ease this dispersal. The availability of drought refuges can also determine how long it may take for local rakali populations to return to areas they had once inhabited.

Rakali recorded during the daytime at Piccaninny Creek, Yanco Creek system, checking out a sardine tin used as lures during research.

Describe your favourite moment while out searching for Rakali.

Some of my favourite moments are when I get to observe rakali going about their lives. I’ve spent countless hours watching them swim about the shallows, foraging for food, with intermittent trips to the bank to eat, or to collect sticks and grass for their den. On one particular occasion in the Lowbidgee I was standing in the water, my hands full setting up a camera trap when one swam right past me barely a meter away. It hardly noticed I was there as it just kept swimming down the creek.

How do you hope your research findings will be used in the management of environmental water?

Thus far, I hope that more monitoring programs will incorporate rakali as a target species, and potentially use some of the survey methods I developed with camera traps or spotlighting across waterways at night when they are most active. I am still investigating how hydrology affects rakali, but I believe the research can provide greater insight into the distances between necessary drought refuges, how the velocity of flows impact rakali and water depths needed to support populations

Where can we find out more about your research?

My paper describing the detection methods of rakali has been submitted for publication and will be titled ‘Putting rakali in the spotlight: innovative methods for detecting an elusive semi-aquatic mammal’. It should be available in the coming months, while a review into the extinction risk of the world’s freshwater aquatic and semi-aquatic mammals is available to read in the Journal of Conservation Biology The final studies on resource use and activity will be completed this year.

Our work in the Murrumbidgee

The Murrumbidgee is a lowland river system with large meandering channels, wetlands, lakes, swamps and creek lines. Our work here focuses on understanding how native fish, waterbirds, reptiles and amphibians, as well as wetland vegetation communities, benefit from these targeted environmental watering actions.

Learn More

The Murrumbidgee River


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