If your are playing ARK evolved or UME you can gather it in just 5 steps within hour,

Step 1. Tame a basilosaurus. ( U can take Itchy and find it, don't worry plesiosaurs and others are to slow.)

Step 2. Change daino damage to 0.3. ( Basically reduce the dono damage according to youself but don't put it to 0.)

Step 3. Go near the Cavern of Lost last hope and search the ground for sea Eurypterid (Sea Scorpion), ( hint, go inside the cave and search the ground, under the bridge. ) it will give 5 to 7 black pearls.

Step 4 ( Optional ) kill tuso inside the cave, don't worry about damage and grabbing, as your basilo is totally immune to that, it'll give 29 Black pearl at once, ( don't forget to reduce damage in settings, and don't worry about alpha mosa, they don't spawn inside caves,).

Step 5 ( optional ) go find the alpha mosasaur at the upper right corner of the map, behind the carno island, for 100 black pearl instantly. ( And don't look for alpha in caves, they not spawn there at all, all are rumors, Reduce damage to 0 or it will tear u Apart XD ).

Theses are the most effective ways (steps) to gather black pearl, on ASE Island, 100 percent tested,