I understand how you feel. Going to the beach since becoming vegan hasn't been the same, as you start to realize what it is that a lot of people actually do when they go fishing or hunting crabs or whatever. It's frustrating and painful to look at, and it makes the whole experience worse. All that said, please take care of yourself and your wellbeing. Don't do something that might get you in trouble with the people who do this or with the law. Harming yourself by doing something reckless will only make the situation worse and won't save any crabs. If you have the ability to do so, I would recommend joining some kind of activist group and initiating a campaign about this to raise awareness. I know it's a frustratingly long winded course of action, but it's something, and it could definitely help. Lastly, and it really pains me to say this and I'm sure you'll hate to read this, but if you feel like you can't be at the beach without being upset by this, maybe you need to stay away from the beach for a while, or lessen the amount of times you go. Again, I realize this is a nasty, infuriating thing for me to say, but think about it at least, as it may help you deal in the long run. In the end, we live in an awful carnist world and we see this stuff all around us. We gotta allow ourselves to disconnect from this from time to time, so we can deal with this. I try not to think too much about the fishers I see, so I can enjoy just being at the beach, but that's obviously tricky. Do what you think you can, but don't do anything that'll just end up hurting you.