I searched uo.com for this and found no written evidence but I think this is correct as far as white pearls are considered as a special resource by the code/devs.
*edit* I keep thinking of this... If fish or even shoes are the primary resources and the pearls are specials, then it should be this way. But as far as I remember a pearl is fished up solely and doesn't come along with any other successful fishing attemp pulling up a fish, shoe or whatever. So it it not a special resource in the classical sense.
Well, this is the theory, logical and all that. But what the devs do is sometimes another thing rolleyes: