The native shell found in Fiji differs from the shell found in French Polynesia. It's the same shell, and I'm not sure whether it would be considered a sub-species or not, but the Fijian shell will often have more of an orange lip versus the traditional shell in FP. The same shell can be found in FP, but may only be 5%, while the shell in Fiji makes up more than 50% of the native wild stock. What this leads to is a color range that has a lot more of the pastels than found in French Polynesia. Also, overall the size is larger and the nacre averages 1.6 mm, vs the .8 mm in Tahiti (this is what I've been told by Justin in Fiji).
One of the reasons they are so much more valuable on the market is because Justin invited European retailers to his auctions, not just the main Japanese wholesalers. A few years ago, Gellner bought most of the production well above reserve, and has been promoting them as Fijian pearls with proven provenance primarily in Europe. They are promoted and sold not as Tahitian pearls or Pinctada margaritafera pearls, but as Fijian Pearls, specifically.