Some fish are radio-tagged, moved above a dam, and tracked to find out if they return to their birthplaces to spawn.

有些在水坝上活动的鱼被安上了无线电标签，可以追踪查看它们是否返回出生地产卵。

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The Environment Agency said while the passage of tagged fish over the barrage had been low, it had found the numbers of young salmon upstream had increased, which underlined the complexity of the issue.

BBC: Fears over Tees Barrage impact on fish

The Angling Trust said it was disappointed after none of 72 fish electronically tagged negotiated the barrage to migrate up river to spawn.

BBC: Fears over Tees Barrage impact on fish