UK Researchers Find Flow Manipulations Could Keep Endangered Eels Out Of Dam Turbines

When you think of popular angling targets, a whole suite of species likely comes to mind: large- and smallmouth bass, trout and other salmonids, perhaps perch and walleye. But what about the eel?

It’s true, eel aren’t the most popular recreational target these days — harvest data show that American eel angling has fallen since it peaked in 1985, and the Marine Recreational Information Program stopped its recreational survey for the species in 2009. But in America and Europe, the eel remains a vital commercial fish, with juvenile American eels, or elvers, selling for $2,600 a pound in 2012, in what Scientific American labeled a “gold rush.”

The European eel, however, has been listed as critically endangered since 2010. Recent reports show that 90 percent fewer juveniles are returning to rivers after spawning. Overfishing, pollution and climate change have been cited as explanations for the species’ decline, but hydropower infrastructure offers a significant obstacle to the migrating fish as they head out to spawn at sea.

A new study from the University of Southampton suggests that increasing flow velocity near hydropower turbine intakes makes eels more wary of the spinning blades, and causes them to seek safer routes. A paper detailing the study’s findings is published in the journal Proceedings of the Royal Society B.

The eel is a valuable commercial fish. Juvenile American eels, or elvers, sold for $2,600 a pound in 2012. (Credit: Maryland Fishery Resources Office, USFWS)

Tracking the movements of 40 tagged adult eels near a manipulated hydropower intake, university researchers found that the fish exhibited “search” behavior when flow velocity was low. This curiosity led the eels to explore underwater structures, putting them at a greater risk of becoming entrained by hydroelectric turbines. But where the flow was manipulated to higher velocities, the fish seemed to more actively avoid the turbines, often escaping upstream to seek another passage.

“Despite centuries of efforts to restore and maintain connectivity for fish (typically by providing fish passes), effective solutions remain elusive under many scenarios,” the paper reads.

The study’s findings, the paper says, offer some insight into potential alternative techniques that could improve fish passage and help protect the endangered European eel.

“This interdisciplinary research provides hope that behavioral deterrents may be developed to divert eels away from hazardous routes during their downstream migration,” said lead author Paul Kemp in a university press release.

Although their numbers are faring better, today the American eel faces many of the same threats as its European cousin. But lack of recreational interest has diminished the quality of data regarding the species, making them harder to evaluate overall.

U.S. fishery managers and riverine infrastructure engineers might do well to learn a lesson from researchers across the pond, before this slender keystone species slips away.