Tbh, all you need to do to kill these is lure them as close to shore as you can and attack with a spear. I’d say maybe 1/30 even hit me when I attack like this, so it’s really safe. Just don’t be underwater for long around them. They look like they are moving slowly, but then suddenly you are being attacked by 4 of them.
If you’re in the water without a tame, as long as it’s shallow backpedaling is almost fast enough to outrun these suckers. Although their stun renders you unable to move, you can still stab it, and they’re squishy.