Why eDNA is Revolutionising UK Freshwater Fish Surveys
- chris10809
- Feb 18
- 2 min read
Why is there so much hype around eDNA for freshwater fish monitoring in the UK?
For 50 years, UK regulators like the Environment Agency have relied on electrofishing and net-based methods to assess fish populations . These techniques—while valuable—suffer critical drawbacks:
Electrofishing misses 40-60% of small/elusive species in turbid rivers like the Thames
Nets like gill and seine selectively target larger fish, skewing biomass estimates
Both methods risk harming protected species and require £3k-£5k per survey
The gold standard for modern, ethical monitoring.
Imagine every fish in a river leaves behind invisible "breadcrumbs" of DNA—scales, mucus, or blood (see more on what eDNA is here). Scientists now use this environmental DNA to track how what fish are swimming in English rivers.
eDNA is non-invasive and avoids harming fish or disturbing habitats , while detecting up to 3× more species—especially small, rare, or cryptic fish .
Unlike electrofishing, which requires optimal water conductivity and misses 30–70% of taxa in turbid waters, eDNA works in all conditions and quantifies biodiversity 50% faster at half the cost per survey .
Gill netting’s spatial limitations and size bias toward larger fish further cement eDNA as the gold standard for modern, ethical monitoring.
But there’s a catch: these breadcrumbs disappear fast—sometimes in less than two days!
Why the rush?
⏳ Fast water = short traces: In fast-flowing streams , DNA gets swept away or broken down by tiny microbes.
🧼 Natural cleaning: Some rivers like Chalk streams are naturally alkaline—like a gentle soap—that gradually dissolves DNA.
So how do you "catch" fish DNA before it’s gone?
1️⃣ Time it right: Sample at dawn, when fish are most active making sure to use specialized filters and pumps to filter as much water with DNA in as possible.
2️⃣ Take multiple water samples to reduce the chance of missing fish .
3️⃣ Freeze or fixate the samples immediately to pause the "DNA clock" to prevent the DNA from breaking down.
Why Everyone Is Excited
Recent studies from the Environment Agency show why eDNA is causing such a buzz:
Triple the Detection Rate: Finds 3× more species than traditional methods
Zero-Harm Approach: No need to disturb or stress fish
Budget-Friendly: Can cut survey costs by 50%
Works Everywhere: From crystal-clear chalk streams to murky urban rivers
The UK Leading the Way
The Environment Agency and Natural England now recommend eDNA as part of their official monitoring toolkit.
Why?
Because it works:
Over 30% of UK fish surveys now use eDNA
Scotland is investing £6.2M to map all their lochs using this technology
It's non invasive approach means protected species (like the river lamprey and European Eel) are better monitored than ever
🌿 A Silent River Still Speaks
As Dr. Linda May recently remarked: "eDNA lets us hear what fish communities are saying without disturbing a single scale."
📞 Get Started Today
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