Working on behalf of water company, Welsh Water, which owns and operates the dam, APEM designed and installed a frame, camera system and ultraviolet lighting on the exit gate of the fish pass. Scale bars on the frame allow APEM’s fisheries scientists to measure and record the length of each fish passing the camera.

So far the cameras have captured migratory trout of up to 45 cm moving through the fish pass. Footage up to early December has so far been analysed, meaning that more fish are likely to be recorded once the full dataset has been analysed.

Paul Gratton, a principal consultant on APEM’s fisheries team, said: “The design of the camera frame has allowed us to process a proportion of the footage with automated motion detection software, which has helped reduce the need for staff to watch many hours of footage to identify fish moving through the pass.”

The fish pass is of the pool and traverse type and was specially designed for the location with a series of automated penstock gates. The fish pass was modified in 2015 by Welsh Water as the previous structure had proved ineffective. It allows fish to migrate upstream and pass the impoundment at Llyn Cwellyn on the Afon Gwyrfai which is a SAC river, designated for salmon.

The river upstream of the reservoir and its tributaries provide important spawning habitat for both salmon and trout.

If you have any queries, please contact Paul Gratton, principal fisheries scientist.
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