Mire-pearlers don't just deal in pearls. They steal, they trap, they take slaves.
Mire-pearlers got mire-pearls from mire-clams. Although this was meant to be their trade, mire-pearlers were also well known for stealing and taking slaves.
Mertin Hoist and his fellow mire-pearlers were employed by Quove Lentis. They attempted to destroy Five Falls but were defeated by the inhabitants of the Farrow Ridges.