Try trapping it it with a type of bated box. A small plexi container, a flat piece of whatever to cover the top, a small rod to prop the door, and fishing line to pull the prop. I had an issue with a wrasse and had to trap it, took 45minutes and a beer's worth of time. Just bait the trap with some food, and you may have to bait it several times to get the right fish. In the image, the wrasse was checking it out just before going in.
Here's an image, hard to see the fishing line, but the idea is there...
Here's an image, hard to see the fishing line, but the idea is there...