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.
WORST THING IN THE GAME!!!!!! They will stun your tame and kill it, regardless of the level. Only the basilasaurus is safe. If they sneak up on you with your mosasuar, they will kill you and the mosasaur