Don't bother searching for black pearls in Ark Mobile! Feed the squid a stack of cooked prime meat after giving it soothing balm!
(This works well on easy servers, check gamepedia for how many stacks it'll need with soothing balm)
Take a raft (make sure there aren’t any Leedsichthys around!) then put a chest on the raft full of black pearls and take 50 at a time. An take a lot of Carbonemys or a basilo and tame. Beware the weight of the pearls!
Swim your tame next to it and wait for the grab, dismount and feed the pearls then swim up, it will do around 2.5k damage before it lets go of your tame so keep that in mind when deciding what to take.
Rinse and repeat
I play on official primitive. And I have tamed 3 of these beasts without loosing a single dino. All you need is a average lvl pleis or Mossi and pump health. Ride the Dino down and stay away from any edges then come to a complete stop and wait until it grabs you. Wait around 2 seconds before jumping off and make sure your dino is set to passive. Swim up to it and feed then swim straight up. Keep going but don't go out of whistle distance. Quick whistle all and watch your dino break free and swim up to you then just jump on and swim up and repeat
Best way I found is to have a good spino with levels pumped into health (preferably at least 20k) and a good saddle if you can. You let the squid grab the spino, you wait a few seconds, then hop off feed it the pearls, make sure the spino is of follow and swim straight up. Just rinse and repeat until taned