AUSTRALIA HAS AN endangered animal that owes its survival to underground pipes. Plentiful in the past in the Murray River, Hanley’s river snail (Notopala hanleyi) was written off as extinct until it was found clogging irrigation pipes near Barmera in South Australia. It has since been found inside pipes near Mildura, but nowhere else. In the river itself the snails have not been sighted since the early 1980s, and then only as empty shells.
This endangered ‘pest’ is a challenge to conserve. The pipes it likes are fully enclosed, more than two metres underground and fed from offtake pipes deep in the river. Only when repairs are done, or outlets on farms inspected, can the snails be seen. In their artificial habitat they reach extreme numbers. Irrigators have in some cases accumulated trailer loads of shells after removing blockages from sprinkler heads and pipes. Chlorine has been used to dislodge them.
Until the 1950s the snails could easily be found in the Murray and its tributaries on submerged logs, rocks and litter, grazing the biofilm of bacteria, fungi and algae that forms on underwater surfaces. Introduced carp may have become one problem, by eating snails and muddying the habitat.
A larger problem are the weirs built along the river to harvest water. Along the lower Murray, pools backed up behind weirs now make up half its length. The biofilms that form in the sluggish water are dominated by mats of filamentous green algae which are poor tucker for snails. Inside the pipes, which are too dark for algae, the snails find the bacteria and other organic matter they need. Water pumped through delivers plenty of dissolved oxygen.
More than two metres wide, the pipes are mollusc havens, providing homes for another four declining snails, and for mussels and clams as well. None of the 18 snail species that dwelt in the lower Murray remains common, except inside a few pipes. But when the pumping stops each autumn, these same pipes can become death traps as the oxygen in the water declines.
You aren’t likely to see a Hanley’s river snail, but I can report that they are 20-25mm wide and dark green or brown. Rather than lay eggs as most snails do they give birth to a small number of live young.
Their plight is so dire the New South Wales government is proposing to lift their status from endangered to critically endangered. Perhaps a name change is also in order, to ‘Hanley’s pipe snail’.
Attempts are underway in South Australia to establish them in wetlands there, and these offer the best hope for the species.