| Summary: | Domaas, S., Orell, P., Kytökorpi, M., Myklebost, M.R., Erkinaro, J., Gjelland, K.Ø. 2024. Evaluation of fish trap and guiding fence efficiency in the River Tana in 2023. NINA Report 2387. Norwegian Institute for Nature Research. Pink salmon (Oncorhynchus gorbuscha) is an anadromous species which spawns in rivers and whose fry migrate to sea shortly after emergence from the gravel. It is native to the Pacific Ocean but was repeatedly translocated to the White Sea during the latter half of the 20th century. Pink salmon has a strict 2-year life cycle, and odd-year populations have in recent years become invasive in the Eastern Atlantic. In the River Tana/Teno, a large Norwegian-Finnish watercourse and one of the world’s most important rivers for Atlantic salmon (Salmo salar), the spawning run was estimated at more than 50 000 pink salmon in 2021.The Norwegian Environmental Agency therefore decided to install a large trap-fence system in the river in 2023 to remove as much pink salmon as possible whilst letting native salmonids through. The Norwegian Institute for Nature Research (NINA) in co-operation with Natural Resources Institute Finland (Luke) was given the task to monitor how the ascending and descending fish responded to the trap and guiding fences. A suite of sonars, camera systems with and without artificial intelligence (AI) capable of recognising fish, snorkelling, and drones were used for the fish monitoring. The results were compared to sonar counts of migrating fish further upstream in the watercourse. A rapid build-up in fish numbers and activity was seen in the area immediately downstream to the trap following the trap installation. However, after a short dip, increasing numbers of fish passing the Polmak fish counting station (about 20 km upstream the trap) indicated that the guiding fences were “leaking” fish. Daily numbers of migrating fish observed in the western channel at Seidaholmen corresponded well to daily numbers observed at Polmak, indicating that this was the main route for fish ...
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