Understanding what wildlife lives in and around our rivers is key to improving the biodiversity of the catchment through strategic habitat protection, management, and restoration. However, measuring the presence, abundance, and distribution of animal species is harder than it sounds. Most animals tend to move around and many of them would prefer to not be seen and disturbed by us humans. Many of our priority species, which are of particular conservation importance, are so rare or elusive that it becomes extremely difficult to detect their presence.  

But now, due to the incredible advances in genetic technology, we can detect the presence of species using environmental DNA or eDNA. eDNA is genetic material that animals shed and leave behind in the environment, whether that be in the soil, water, or air. In the same way that a researcher might look for things left behind by an elusive species (like tracks, scat, or hair) eDNA is another “clue” left behind by animals when they pass through the environment that we can use to detect their presence.

As part of our developing strategy for protecting and restoring tributaries of the Thame, which arise in the Chilterns chalk escarpment, we have been investigating the presence of the iconic, native brown trout (Salmo trutta). Read more about brown trout here and here.  Initially, we are focusing our investigations on the streams that feed into the Kingsey Cuttle Brook, including the Horsenden Stream, a designated chalk stream.  This river network, close to Princes Risborough, is known to have historically been the home of the wild brown trout.  The project is funded by the EA and is delivered in collaboration with the Chilterns Chalk Streams Project team.  

Surveying streams for fish species is notoriously tricky, netting and electro-fishing methods are expensive and time consuming. And even if you are lucky enough to observe rare fish species in your local streams, it can be difficult to verify the exact species solely from visual observation. That’s why our Project Officers, Andy and Chelsea, completed surveys in the Kingsey Cuttle Brook and its tributaries in March 2022, which included gathering eDNA samples. Our team went out with aquatics expert Peter Kimberg of NatureMetrics, who supported the sampling.  

About 2 litres of sampled river water is passed through an extremely fine filter that captures eDNA. The filters are then filled with preservatives and sealed to prevent the captured DNA from breaking down. It only takes a tiny fragment of DNA to detect a species, so it’s very important to wear PVC gloves and adhere to sanitary sampling methods during the sampling process.  Any contaminants (even DNA fragments from your lunch!) can potentially show up in the sample analysis.  

Our samples, collected from 6 different locations across the network are currently in the lab for analysis. To maximize the amount of biodiversity information we gain from these samples, we have ordered analysis for both fish and mammal species. While our priority is to determine the presence of brown trout and assess how they can be introduced, we are eagerly awaiting what other surprising species might pop up in our samples! Watch this space for updates.