Using a quetzal, kill the ones on the surface for easy bio toxin, then use it to make shocking darts, which are better than tranq darts, or use the bio toxin as a better narcotic for being Dino's torpor up
While they are dangerous they are the greatest source of narcotics in the game. They give what’s called bio toxin and this will make torpor rise faster. If you want to kill them safely lure them to a raft and then crossbow them down. They are fairly weak so you won’t need many shots to slay them. Your greatest worry will be the sharks but if you can kite them into these guys you will find it works to your benefit.