This is a frequently asked question. The short answer is that there is no difference.
Rarotonga and Tahiti are geographically right next to each other so the sea conditions are identical. Furthermore, the oyster (Pinctada margaritifera) that is used to cultivate the pearls is exactly the same species in both countries and the farming techniques used are alike. Lastly, the ratio of low quality versus high quality pearls is proportionate.Because the pearl industry in Rarotonga (exporting less than USD$1 million per annum) is much smaller than Tahiti (exporting USD$100 milllion) there is a perception that there is a difference in quality. While there is a big production difference, again there is no difference in quality. Moreover, Tahiti spends several million per year marketing their pearls around the world so it’s name recognition is much stronger.