Are sharks a problem in Bora Bora?

Could you elaborate on the potential threat posed by sharks in Bora Bora? Are shark encounters a common occurrence for visitors and locals, or are they a rare sighting? Are there any specific species of sharks that are more prevalent in the area, and what measures are in place to ensure swimmer safety? Additionally, are there any precautions that visitors should take when swimming in the waters surrounding Bora Bora to minimize the risk of encountering sharks?