We've caught them from Outer Banks, North Carolina piers and from a bridge and boat both inshore and at the reef in the Florida Keys. As humble by name and size grunts are, they fight very hard on light tackle for fish without pelagic build (but look at the shoulders), and they taste great from the pan. That photo of the open mouth reminds me of a philosoraptor dinosaur. The coloration is for their peculiar kissing behavior, actually a territorial face off. Fish do some weird things; the grunt also is named for the pig-like grunting sound it makes. They don't sound exactly like wild boars the way Floridian pig frogs do (amazing to hear at night in the Everglades), but the mandible features without the mouth opened wide like that in the photo vaguely resemble pig snouts. The blue-gold wavy patterns on the head give a stunning view, and the eyes seem as innocent as a Pollyanna cartoon figure.
Most of them measure about 11 inches long and take shrimp, frozen or live, with a firm whomp. Set the hook pretty quick or suffer it swallowed. Even with 20-foot depths, unless current is strong and/or wind brisk, a good-sized spit shot is sufficient. Since grunts have no disarming teeth, mono is fine, and we go with six to 10-pound test. Ten-pound test relieves the nerves when a big fish opts for a shrimp, which happens in the Keys inshore waters and certainly the reef. I hooked something five years ago I may not have been able to hold had the hook not pulled. But light tackle is light tackle and you can't compromise if you use it. The best you can do is turn the key on the outboard and follow along. Perhaps if the fish does not dip into coral and fray the line hopelessly, you'll gaff it.
If wind turns the boat into a trampoline, go with a half-ounce egg sinker, possibly three-fourths ounce. A size 2 plain shank hook is all you need besides a disgorger on occasion. Drift or anchor. Either way produces, although anchoring can draw fish in that become interested in the action rather than spooked. From piers--again--shrimp is best. And avoid those heavy sinkers. Conventionally named "saltwater," they're just conventionally convenient, the default choice against the extra step of thinking that lighter may be better--and usually is.
Action with grunts can be episodically non-stop and typically alternates with runs of other species like snappers south, and spot and croakers northward. When we fish shrimp, we hope for an unusual, large fish and almost invariably hook up with one. We also take a few grunts or other legal panfish and use them for cut bait, which results in fewer but larger fish. And some more grunts.
I like to take a few for dinner and breakfast. Scaling a grunt is like scaling a bluegill. The large, abrasive plates resist difficultly, and like sunfish, the fins can smart. Just make sure the fish remains moist or take them directly from the live well to the cutting board. No reason to grunt even if you bloody your own skin a little.