Prognathodes basabei butterflyfish off Pearl and Hermes Atoll, Northwestern Hawaiian Islands © Greg McFall/NOAA
A new species of butterflyfish, the Prognathodes basabei, has been discovered in the coral reefs of the Papahānaumokuākea Marine National Monument, a conservation area in the Northwestern Hawaiian islands. Finding a new butterflyfish is a rare event, as according to Richard Pyle, lead author of the study to classify the species, "butterflyfish are the glamour fish of the coral reefs… they are colourful, beautiful, and have been very well-studied worldwide”.
The find, published in ZooKeys, comes after two decades of waiting. The species was first observed in video footage from manned submersibles in 1998. There was only one problem: the footage was filmed at a depth of 180 metres, and until now the technology simply didn’t exist to send scuba divers deep enough. Now though, advanced electronic closed-circuit rebreathers, special apparatus that reuse the oxygen from every exhale, mean that divers can plumb to new depths of 100 metres below sea level.
In June, technical divers went sufficiently deep to collect specimens that could be preserved well enough for scientific measurements. They even managed to collect live specimens in June, which are now on display at museums around Hawaii. Measurements revealed substantial genetic differences with other known butterflyfish species, as well as differences in the body depth, head size, number of spines in the dorsal fin and colour.
Recently, the new fish has been encountered more regularly, on more exploratory dives in the area. The “coral-reef twilight zone” (or more formally the mesophotic coral ecosystem) between 45 to 150 metres down is an exciting area, because it is still mostly unexplored – it is too deep for traditional scuba divers, but shallower than most submersible-based exploration. Now that technology is catching up, divers can explore more. They have already found a variety of new species of algae, mites and even crustaceans, and many species previously believed to only inhabit shallower waters, where the reefs are sadly declining.