We’ve all seen those gritty TV dramas that have astonishing science and tech at their fingertips to analyse the DNA from crime scenes. Turns out much of it is not all that far-fetched! We now have the ability to use ‘genetic breadcrumbs’ found in our stream water to identify all manner of different species – from microbes through to mammals.

The Graeme family kindly used an eDNA kit they were given to conduct sampling on the Aongatete and Whatakao rivers early this year. There was no expectation of what might be found, but we were hopeful of something exciting. Do we perhaps have the ancient and elusive Hochstetter’s frog at Aongatete, for example?

Well, sadly there were no frogs, but we were delighted to be told by the director of the laboratory, Shaun Wilkinson, “These must be special sites. It’s rare to see so much species diversity from just two samples!”.

The highlight was the shortjaw kōkopu, our freshwater fish taonga species that is classified as threatened with extinction. This finding has been notified to the Migratory Species Aquatic Unit at DOC, as they are putting in a lot of effort trying to understand the distribution of shortjaw kōkopu around NZ.

Along with the shortjaw kōkopu, the other ‘whitebait’ species (īnanga, koaro, giant kōkopu, banded kōkopu) were detected, along with both the long fin and short fin eel. There were 7 caddis fly species and 5 mayflies – all indicative of healthy waterways. At least two dozen other insects and spiders were found, plus 12 species of worms, including the plentiful ‘sludgeworm’ and the much less common ‘red wriggler’!

What about higher up the food chain?  Perhaps unsurprisingly, red deer, possum and black rat were found, plus human DNA (ewww). Very little sign of our more obvious feathered forest-dwellers though; a little bit of chaffinch and goldfinch DNA in one of the streams, and some ruru/morepork in the other. We’ve surmised that perhaps they don’t leave much evidence in flowing waterways as they spend relatively little time in them bathing or pooping?

We’re very keen to conduct more sampling, as we take relatively small volumes of water per sample, after all. As the science around eDNA evolves, it may be that a bigger number of samples from the same site are needed to find every species present. It comes down to the cost of testing versus the relative benefit.

What we have gained is a fresh appreciation for the huge number of organisms that currently live in our streams, the vast majority of them unseen. And it would appear that what we consider to be lovely clear and ‘clean’ water is, in fact, DNA soup!

What is eDNA?