SCIENCE IN ACTION VERSION REPRO OP
MEET THE EEL DETECTIVES Ingenious technology that enables detectives to catch criminals is set to revolutionise our work to protect elusive endangered species. Derek Niemann finds out how it all began with a fish as ‘slippery as an eel’…
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ast summer, volunteer citizen scientists were scouring waterways and ponds to help a special fish that is critically endangered. But they weren’t actually looking for eels – they were testing the water. Nobody is in any doubt that European eels are in deep trouble. WWT’s Principal Research Officer, Laura Weldon, has spent the past five years studying them: “Numbers have plummeted in my lifetime. There are now so few, and yet they are still so understudied because nobody was particularly interested in them before – they were everywhere.” And eels are a valuable guide to the health of a waterbody, since they are both predator and prey.
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PRODUCTION Eel image: Neil Aldridge/WWT
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THE QUEST FOR KNOWLEDGE Laura is grappling with understanding the causes of their decline. “We are keen to start mapping eels to find out exactly where they are. Part of the reason for eel declines is that there is insufficient good-quality habitat in which they can grow and stay healthy. We’re interested in learning where they are and why. Are they making it upstream to mature? Which barriers, such as weirs, can they get past and which are impassable, and what are they doing when they get through? Traditionally, it was only the older females that were found far inland and their numbers have just dropped and dropped. Exactly how far are they getting?” Eels are notoriously tricky to monitor. Despite their silvery bodies, they are often hard to see, slinking between waterweeds,
eDNA registered eels in places where nets had come up empty at the first time of dipping 30
Waterlife
MARCH/JUNE 2022
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or obscured from view by the sun’s reflection on the surface. Given their scarcity over such a huge network of watery possibilities, they are difficult and expensive to catch with conventional fishing nets. Hauling them out of the water is an invasive way to count such a rare species too. Could there be a more benign method of detecting their presence? One answer lies in a branch of science that has expanded exponentially, ever since police detectives discovered that criminals do not simply vanish without We used to have to catch eels in order to confirm their presence in the lakes around our reserves. Now we can just sample the water for their DNA
trace from the scene of their crime. Invisible and irrefutable evidence remains; the unique DNA that every human leaves in their blood, hair and even flakes of skin. Within the past few years, conservationists have begun to apply the same forensic techniques to wildlife, seeking environmental DNA (eDNA). And such techniques appear to work particularly well with creatures that live in water. Simply collect the water and, if an animal is present, strands of its DNA, its genetic signature, will be there.
