Pearl Diver
Proc
Chance for a bonus pearl/tertiary on each catch.
Rolls between 3% and 12%, scaling with the gear score of the item carrying it.
Forge mods that grant it
Spending one of these puts the perk on your gear instead of waiting for a roll.
Rolls on
Fishing Rod
A drop or a craft of these types can roll this perk into one of its slots.