Been a real problem for years. I remember finding a 40 foot gill net strung across the Pilchuck during Coho season years ago, it was a local that lived on the river. We did get the net (22 Coho in it) out and when he came out of the woods and threatened us we took the risk and charged him, held him down, went into his own house and called the cops. He got fined and lost his license for 5 years,,,,like he cared about that!
Point is, there are just so many losers out there doing [Bleeeeep!] stuff, it is hard to stop them and they know it.