Scientists say deep coral reefs in the Papahanaumokuakea Marine National Monument may contain the highest percentage of fish species found nowhere else.

A study published in the Bulletin of Marine Science says nearly 50 percent of the fish scientists observed over a two-year period in monument waters 100 to 300 feet deep are unique to Hawaii.

The monument said in a news release Thursday that’s a higher percentage than any other marine ecosystem.

On deeper reefs, the scientists found more than 90 percent of fish were unique to the region. Only specially trained divers using advanced technical diving methods may reach these deeper reefs.

Co-author Randy Kosaki says the richness of unique species in the monument validates the need to protect the area with the highest conservation measures available.