Those M-80's are actually seal bombs, I have used them numerous times and they usually, but not always scare them off, I have caught fish within 5 minutes of throwing 1. I have never seen any smoke from 1 that went off underwater but I do occasionally hear a kind of muffled "whumpf" (thats the best way I can describe it) but you have to be within probably 100 yards to hear it. 1 piece of advice for anyone thinking of using them throw them away from the boat, a friend of mine dropped 1 over the side of his fiberglass boat, put about an 18" crack in the hull.

As for the original question, I'm releasing the fish because I think there is a good chance the fish can escape a seal as long as he's healthy when released. Seals/sealions are looking for an easy meal, fish are alot easier for them to catch when there attached to your line.