That's not just robbery, but silly robbery, I would think: maybe stressed mussels produce more pearls... but still... what could those fellows hope to obtain from 130 mussels? Jail sounds more likely (un-likely such as is) then a single notable pearl.

Any idea how many pearls might still be in the wild in such a small population of relatively young mussels beds? (assuming they are 'young', since the beds only just recovered from near-wipe out)

Someone should inform those bastards to fish where both they, and the local mussels stand a chance