08 Sep 2017 Murray Crayfish Part 4: They’re not in SA, but they could be… the search continues in the Lower Murray
After four years of searching, which included over 7700 net hours (number of nets per site times by the number of hours each net was set for – that’s also 321 net days), at almost 30 sites we have failed to detect a single Murray crayfish in the South Australian section of the Murray River (e.g. the Lower Murray) – we can’t rule them being present somewhere but obviously, any remnant population will be small. That said, we sampled likely sites – those with reasonable flow (which is largely lacking in SA) – as well as several anecdotal records (thanks to the Field Naturalists of South Australia for funding sampling this year).
Whilst we haven’t tracked down the last official record, we believe that it will be from the late 1980s (at that time, Bob Hawke was prime minister, John Bannon our premier and Adelaide had only held the grand prix for a couple of years!) – that’s a likely absence for thirty years.
Where to from here?
Given the timeframe that they have been absent we could except that they are regionally extinct and stop there. Or, we could acknowledge their absence but work toward re-establishing them in South Australia. I prefer the latter for several reasons.
Firstly, they belong here – the species historically occurred in the Lower Murray all the way downstream to at least Murray Bridge (there is even a record from the Lower Lakes!).
Secondly, despite the regulation of the Lower Murray by a series of weirs, which act to stabilise water level and reduce flow velocity (that is mixing of the water column), there are sections still that maintain suitable habitat, which could support the species. Additionally, other threats, such as pesticide run-off have been minimised.
Thirdly, they need a hand to get back to SA. Some will say that if there they were meant to be here now they would be, but as the nearest population is over 300 kilometres upstream and they limited dispersal mean that it will take hundreds of years to recolonise. Additionally, having just completed translocations further upstream, we are in the best position to make them happen in South Australia.
Lastly, they are captivating species that could promote greater awareness of the river and can provide an indicator for the success of present and future river restoration in the Lower Murray. We don’t think that they will ever be widespread again, but there is potential for locally abundant populations to persist.
So, let’s turn attention to re-establishing them into SA! #murraycraysforsa