Just go to eldrich zone on crystal isles and look for big bubbles that have some black clams/oysters inside of them, put your angler fish inside the bubble, harvest, and enjoy the best black pearls harvester in the entire game, super easy, rank up for people to see this.
On the new map, Lost Island- there is a sunken ship in the very bottom left corner. I mean, tucked almost right in the corner, where the barriers meet. If you go inside the sunken ship, to the bottom of it, you will find clams full of only black pearls. The devs have a sense of humor, I'll give them that!
On Fjordur, the only way to obtain Black Pearls without going underwater is through, one, the Magmasaur den at the volcano in a cave inside the Fire Wyvern den, or two, from taming Gachas found in Asgard. Hope this helps anyone playing on the new map.
On mobile single player, frankly, nothing works better than this: save before accepting your gift, then restore over and over until you are gifted 20 black pearls. Clearly lazy, but faster than the alternatives.
When you want black pearls in great quantity, here are some things I suggest.
1: Ragnarok: Vikings bay. Bring a good crossbow to one shot any water scorpions, they drop TONS of black pearls.
2:Extiction: Gachas. Sometimes when taming gachas, you can get one that produces black pearls. They produce in big quantities, and for me is by far the safest and easiest way to get the black pearls. Like if this helps!😄
"This is for only mobile players. Just tame a otter and turn on his/her victim item collection from the corner side of your device and give his/her agreesion to attack target and whistle it to follow you. Then go to small fishes and punch them and wait for some time. Keep warned that your otter's have to kill and hervest that not you. If the otter kill and hervst the fish then it will give you black Pearl. But it has only 35.78% chance to give you black Pearl.This is the tip to get black Pearl safely without any damage. Jay hind