The south-west of WA is home to a large number of freshwater crayfish, many of which people will not be aware of. There are a total of eleven species of freshwater crayfish native to the south-west (plus one introduced species - the Yabby, Cherax destructor); these include five species from the burrowing Engaewa genus and six species from the Cherax genus including the Koonac (Cherax preissii) and the well known Smooth Marron (Cherax cainii).
Catching freshwater crayfish is a past-time of many people in the south-west region, with the Marron season running each year from early January to early February. Unfortunately however, in their attempts to catch the introduced Yabby or native Marron, many people use illegal traps such as opera house / cathedral traps. The use of these traps can unwittingly trap turtles (see image at the end of the blog - caution: image may cause distress) and water rats endangering both species to a fate of drowning. The Smooth Marron is widespread and probably the most well known species of freshwater crayfish in WA, however, it has a close "relative" in the Hairy Marron (Cherax tenuimanus). The Hairy Marron is distinct in appearance from the Smooth Marron, with the most notable characteristic being the presence of short hairs along the head and occasionally the tail. Unfortunately the Hairy Marron is listed as Critically Endangered and according to the Department of Fisheries it is estimated that less than 1,000 hairy marron are left in the wild (to put this number into perspective, the Panda, one of the most well known endangered animals in the world, has a current population estimate of just over 1,800 remaining in the wild). The current population of Hairy Marron in the Margaret River is under threat on many fronts, with the most pressing being competition with the Smooth Marron which was introduced to the Margaret River in the 1980's. The Smooth Marron not only outcompetes the Hairy Marron through aggressive interactions, but it also has the ability to cause hybridisation through breeding with the current population. The Hairy Marron is now extinct from the lower reaches of the Margaret River but can still be found in the head waters. Thankfully there is ongoing research trying to reduce this threat and to help bring the species back from the brink. The species is currently being captive-bred at the Pemberton Freshwater Research Centre with the aim of increasing the gene pool and establish a breeding population. If you have seen suspected illegal fishing activities (e.g. fishing for Marron out of season, the use of illegal traps) get in touch with the FishWatch phone line at the Department of Fisheries on 1800-815-507 and provide as much information to them as possible, such as the number of people involved, what you observed including equipment used, precise location if possible - if GPS location is not possible you can use landmarks, intersections with roads etc. Further reading
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The nightfish (Bostockia porosa) is a species of freshwater fish endemic to south-western Australia (meaning it is found no where else in the world!) and as the name suggests is active mostly at night. The nightfish is carnivorous and has been documented feeding on a range of taxa, including ostracods, gastropods, amphipods and even decapods (e.g. consuming parts of freshwater crayfish). The species has had limited research, with the biology of the species only being described in a paper in 1990. However, more recent broad sampling by freshwater ecologists has begun to decipher the mystery and expose the threats the nightfish faces.
A study by Beatty and colleagues published in 2014 documented large downstream movements of juvenile nightfish in tributaries of the Blackwood River (e.g. Milyeannup Brook) during November and December, as well as migration in the species being significantly associated with surface water discharge. The findings of movement predominantly in the tributaries of the Blackwood River supports earlier research by Dave Morgan and colleagues. A paper published in 2003 found increasing salinity in the Blackwood River had caused the extinction or massive decline in a number of species from the main river channel itself. Whereas the tributaries containing natural forest vegetation and lower salinity levels still contained species such as the nightfish. Although the nightfish is one of the most widespread native freshwater fish in the south-west region, salinization is an ongoing threat and is causing the decline in populations in many of the river catchments. The problem is unfortunately exacerbated by climate change in the south-west where average rainfall has declined drastically since the 1970s leading to even greater decreases in runoff/discharge and altered groundwater levels. The protection of the species in the south-west is now reliant on the preservation of high quality habitat, particularly in areas that remain uncleared, as well as the potential for intervention through the creation of artificial wetlands within the natural environment. Fun fact! The nightfish is one of several native species of fish that host the glochidia (parasitic larvae) of the native freshwater mussel (Westralunio carteri) Further reading
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AuthorMy name is Garry and I am extremely passionate about the environment. I have completed my BSc. Conservation and Wildlife Biology with First Class Honours and have worked in the Environment sector since 2009. Archives
September 2019
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Photos used under Creative Commons from sean.kelleher1, BioDivLibrary, BioDivLibrary