Freshwater aquatic species are in sharp decline around the world and the South West global biodiversity hotspot in Australia is no exception.
Only seven years ago Murdoch University researchers found distribution had reduced 49 per cent in the region for the state’s only freshwater mussel, which spreads when larvae latch on to passing fish’s gills or fins, grow in a little cyst then drop to the riverbed.
Carter’s mussels, dried out after being stranded by drought.Credit:Alan Lymbery
The report compared historical museum records for where the mussel was found with a South West-wide survey to see where they still existed. It resulted in the species being listed as vulnerable on the federal list of threatened fauna.
A follow-up study on Carter’s freshwater mussel, which can live to be as old as 70, published last month in Hydrobiologia detailed how none of the bivalves could be found at six out of 32 sites examined for the paper.
Murdoch University Centre for Sustainable Aquatic Ecosystems director Professor Alan Lymbery said he could not put his hand on his heart and say the mussels were definitely gone from those six sites but not finding a trace of them was still concerning.
“That suggests the decline is still occurring,” he said.
“The upside was where we did find them, we actually went out and looked at density and size and age structure of the population, the populations seemed to be in reasonably good shape.
“For those sites that were still there they all had young mussels, less than 10 years old, so they’re still recruiting to those sites.”
Coming across a pocket of mussels can be deceiving with hundreds found in some locations and thousands of the creature still in existence.
Increasing salinity inland has meant the mussels are mostly restricted close to where rivers meet the coast.
Lymbery said the main purpose of the university’s latest study out of the Harry Butler Institute was to get a better understanding of the mussel’s habitat preferences with a view towards future translocation or even captive breeding.
“Which is what they do in the United States and Europe. Freshwater mussels are in decline everywhere,” he said.
“They like to be close to the riverbank, they like fine sediment rather than rocky or pebbly substrate and they like to have debris in the water, branches that have fallen.
“We’re working with the Water Corporation to see where the mussels can live in their assets like drains and compensation dams.
“We’re having to think fairly laterally because we’re running out of water.”
River flows have fallen 70 per cent in the past 50 years after a massive drop-off in annual rainfall for the South West since 1970.
The reduction in water has meant there are rivers and lakes which dry out in summer and autumn when they previously would not have.
The dry conditions have seen a big drop in invertebrate species across 17 Wheatbelt lakes going from 300 to a bit over 100 between 1998 and 2011.
“All our animals are adapted to dry season pools but they’re becoming fewer in number, smaller in size,” Lymbery said.
“Summers are getting hotter and longer, mussels and everything else have to survive in those refuge pools longer.
“That’s going to be the major problem going forward, that’s why we’re starting to look at artificial structures that might serve as dry season refuge pools, not just for mussels but freshwater fish.”
The South West has 11 native species of freshwater fish, relatively few, but nine of them are endemic.
It’s a trait similar to other Mediterranean climates around the world that tend to be “arks” for unique species.
A recent paper from University of Western Australia researchers examined where the 11 species were likely to still be able to survive come 2080 in a drying climate.
Two fish, the trout galaxias and the WA salamanderfish, a relic from when Australia was part of the supercontinent Gondwanaland, are predicted to have no habitat left in the next 58 years.
Five other fish will lose 80 per cent of habitat and there was a “coldspot” identified in the Shannon River Basin in the Great Southern region.
About 93 per cent of the coldspot is within already established protected areas, like national parks.
Most of the surviving fish species would be present in the coldspot but only 26 per cent of surrounding areas where they could also continue to exist in the region is covered by conservation reserve boundaries.
The nightfish is one of the nine endemic species to the South West of Australia.Credit:Stephen Beatty
The authors suggested just having protected species status or protected areas in isolation may not be enough to conserve the different species.
“Instead, a multi-pronged approach is likely to be more effective, using a combination of protected areas, controlling alien species, and enabling the allocation of adequate environmental flow,” they said.
“The results of this study indicate that changes in species distributions as a result of climate change should be considered in the design and implementation of protected area networks.”
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