The Hawaiian Rock Damselfish is a dowdy little fish. No bright colors, no interesting morphological features. Just a shy little fish. What it is, though, is uncommon. Enough so that when I tried to enter a sighting of this fish into a citizen-science database the computer flagged my entry.
The nonprofit REEF (Reef Environmental Education Foundation) runs an extensive, worldwide network of volunteer fish surveyors. Volunteers are required to take a range of fish ID tests and are given proficiency ranks based on the difficulty of tests they’re passed and how many surveys they’ve conducted. Having only done five surveys to date, I’m still rated as a novice, so red flags went up when I claimed that I’d seen Hawaiian Rock Damselfish at Mahukona. I got an email from the REEF volunteer coordinator telling me my observation had been flagged. The email asked if I was sure it was really a Rock Damsel or if perhaps it was a similar-looking but much more common Hawaiian Gregory. Apparently the Rock Damsel had never been recorded at Mahukona. Fortunately I was able to provide photos.
I’ve actually gotten pretty good at identifying the Rock Damsels by their behavior. They spend most of their time in dark recesses between rocks, with brief, nervous forays into the open. (This makes them really hard to photograph.) Gregories tend to behave this way too, but less so than the Rock Damsels. The difference is subtle but quite consistent. By the way, both of these species are endemic.