They may seem calm, and won't be dangerous most of the time, but don't be fooled: They boast descent damage and godlike resistance, think of them as Rock Elementals of the sea, exchanging HP for numbers.
Just like elementals, they have a small aggro range, very slow movement speed and not the highest of the DPS. But if you get cornered, be ready to suffer a slow death by their stone-crushing jaws.
If trying to tame one make like a wyvern trap on the bottom on the ocean and hive someone else shut it. I use a sarco to lead it in the trap. On the center you can make the trap right next to the air bubble to escaped in the Airr away from any attack range and have a keypad to shut it. This will allow you to use any tranq attack
On the center make dunkleosteus quite the pest when trying to gather silica pearls or other deep water resources. If one is provoked by combat or getting too close other dunkleosteus will come to attack you from very far away and it is almost impossible to escape once they swarm you or your tame.