Threatened mollusc

Cape Town - Scientists had no idea they were there – but otters did.

They are live specimens of a rare freshwater mussel called Unio caffer and they make a tasty meal for otters.

It was the remains of an otter’s meal that alerted researchers to the presence of this highly threatened mollusc in the river running through Oorlogskloof Nature Reserve in the Northern Cape. The researchers were not looking for mussels, but were studying the endangered Clanwilliam sandfish in the nature reserve north-east of Vanrhynsdorp.

While they were wading along the river counting fish, Bonnie Schumann, of the Endangered Wildlife Trust’s (EWT) Drylands Conservation Programme, looked down and saw bits of shell.

“What made me stop mid-fish count and go off with a digging stick was that alongside me were the remains of a fairly recent meal in the form of an opened mussel with bits of stringy meat on it. Otter left-overs unexpectedly provided sure proof there were mussels in that pool,” Schumann said.

After digging around in the river gravel on the river bed, she found a live mussel.

Christy Bragg from EWT’s Cape Critical Rivers Project said there had been only one other sighting of the mussel in the Northern Cape, near the Orange River.

“So this was quite a find. It was because there were still bits of mussel meat on the shells that Bonnie went out and looked for a live one, and it worked.”

The mussels have been in sharp decline in numbers and in distribution for years and are now listed as “near threatened” by the International Union for Conservation of Nature.

Bragg said the find highlighted the importance of the Oorlogskloof Nature Reserve as a sanctuary for threatened fish species, for the Bokkeveld Sandstone Fynbos, and now for the mussels “which were a great indicator of water quality”. – Cape Times