eDNA used to find a Blind cave eel

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Fifteen years ago, a sample from deep in the Pilbara water column turned up an incredible find.

With no eyes, and skin that ranges from translucent white to pink, the Blind cave eel (BCE; Ophisternon candidum) is as other-worldly as it is elusive.

In tens of thousands of samples taken since then, only 11 more have been captured.

The BCE is a listed as vulnerable, and its survival prospects improve if we know where it is, and are able to monitor its presence over the long term.

We knew there were Blind cave eel populations in the Robe Valley, because specimens had been found in eight sites, but the real question was – how do you monitor a mostly uncatchable fish?

Pulling water samples from subterranean aquifers far underground and hoping the sample will include a target species is a bit like looking for a needle in a haystack.

The answer lies with technological breakthroughs in using DNA to identify species present in a region, without having to catch the animal itself.

Environmental DNA uses a DNA ‘hook’ to seek a match in the contents of a water sample. Water contains the DNA of any animals that have lived, died, defecated or urinated in it. When we add an ‘assay’ to this water – a ‘hook’ to which the target DNA will bind – we are looking for a match with that species’ DNA in the sample.

This means we can pick up the presence of a target species through its excrement or remains, rather than having to catch a live specimen. Better for everyone.

What did we find?

Since 2017, the number of sites where we know the BCE is present has increased from 8 to 40, mostly through the use of eDNA methods.

This includes new territories where previous methods were unable to capture evidence of its presence– in the neighbouring Fortescue catchment and further upstream and downstream in the Robe River. Since 2023 we have been using a new qPCR assay, developed in collaboration with eDNA Frontiers and Rio Tinto, to detect the eel in a cost-effective way.

In total, blind cave eels have been detected using eDNA in 93 different samples.

In the end, a better understanding of this elusive creature’s full range means more effective monitoring, and a greater chance of conservation.

We are still discovering the limitless potential of eDNA – including its ability to fill in the gaps where previous sampling methods didn’t give us the full picture.