An ex friend used to do it at the weir when the salmon were coming up the river. He would wait for them to jump up the weir and the fish would be in the water flow for a few seconds trying to swim against the flow to get over the weir. He hit a few and recovered them.

He got caught by other fishermen who reported him to the police . He got the rifle taken off him and marched 1/2 a mile to the police station.

I had stopped going fishing with him months before due to his poaching . I bought the relevant permits and he did not. And he tried to use my permit if we were stopped by the water balliffs.
He lost the rifle and got a caution. He had a new rifle days later .he is still a thieving twat to this day. This was 25 years ago.