I am glad you recycle everyone should. Every product should be made recyclable, and food should be composted. The composting I must admit I need to work on.
I dont like guns they are loud and like you said you are to far away to kill instantly, the seal would just swim away. Also gun powder is probly not good for scavangers to eat, and the bulet hole makes the pelt in some cases worthless. I know some people who own a farm and a possum got into their grain and ate a lot of it. They tipped over the barrel it was in and tried to shoot it. Even at close range it took over 10 shots to the head to kill it. Possums always are in pairs so they went after the other one but instead of shooting it they hit it once with a club and it died instantly. Its sad that they had to die but they kill their chickens and eat their grain, they have also attacked them and their dogs (german shepard mix its huge like a pony). I have used a gun before (wooden targets only) and they are hard to hit percisly in the right spot especially black powder rifles (they smell nice/odd and are fun very Jack Sparrow). In order to kill instintly you would have to hit the brain stem, that would be insainly hard to do on every seal. I saw a deer once that a guy my aunt knows killed the guy hit it in the leg, he could not use the entire leg because it brused so badly. Cross bow could be used at close range except it might fly back at you. Although I can make a bullseye I sometimes horibly miss and it bounces off stuff and lands in the ceilling. That usually sends a few bullet cases showering down on us, we are not the only one who hits the ceilling I guess.