Ok, you have to define the term grouper for people on I
Here, because it has different connotations to each reader, based on their location and type of grouper they prefer to target. To the guys in Florida, they are an abundant fish in caught on just about anything in many depths of water. Here in Texas, when you say grouper, there are 3 thoughts that pop to people's minds deep water for yellowedge misty snowy etc, big grouper fishing targeting Warsaw, and what I instantly thought when reading your post: scamp fishing.
To be honest, scamp fishing is one of my favorite past times and a good friend of mine, Capt. Timmy of the dolphin express and I have always had fun side beds with them. He's definitely better than me, and if you really want To learn a lot more, go blinker fishing with him in the cold months.
For what it's worth, the rig is hardly fine, while there's some technical mods we have whittled down to hear perfect over the years, as well as technique tricks that help. However it's never perfect, and with the snapper problems we have, knowing when to continue or quit is important.
For the rig, my version is very similar but has some special changes. To start with, I make sure to use an ultra sensitive pole with straight braid so I can feel a grouper even sniff the bait 180-360ft down. [Describing the setup gets a bit difficult, so after reading the how to, picture the basic layout of your rig in your head, and extrapolate] To this I tie on a small swivel and a 2-3ft section of 50# fluorocarbon. I tie a 4/0 black. Eagle Claw laser 196L circle (a bliner hook) to the end with a home miller knot. 6-8 inches back from the hook, I put a 3-4" loop. The loop is for the bank sinker, and the weight used varies, but is the lightest that is available and will go fairly straight down with the current.
When picking out the bait to use, reverse thinking is in order. The smallest ones are the best, I'm always hunting for 1.5-3" perch only using larger ones when I'm forced to. The larger baits catch some scamp, but also attract more snapper and amberjack. But scamp like the little ones better. A trap is better for acquiring than a pole.
Fishing at a Port A dock before a trip, you may have caught a few piggy perch, but more likely caught longish. It's ok, it's a colloquialism here, in local vernacular the terms are almost interchangeable. Piggy perch have a more streamlined body, slightly longer snout with squiggles on the side, and meatier lips, plus they usually grunt. They are less common but a better bait. Pinfish are a taller fish , that look a lot like a miniature pissed off steelhead, with sometimes vertical striping, pokey fins, and some mean little teeth behind thin lips. If you said, "Ouch"! while baitfishing you almost definitely had pinfish.
You asked about dead perch... One of 2 things happened if your perch was dead after being down only 3-5 minutes" either you killed it, or a fish did. Although perch are typically thought of as inshore fish, they are a member of the porgy family, and are found in many varieties out to 300 feet. They are actually pretty hearty when treated right. When you hook your bait, be fast and efficient, and get him from the live well to the water asap. Picking the smallest lively perch, cradle him in your hand lightly but with enough pressure to keep the fins held back and from losing him. If you can keep his nose sticking out with your hand still covering his eyes, that's best. Your tackle should have been ready to drop before approaching the live well, so grab your hook with the other had and pin him in one cheek and out the other. This hook placement accomplishes 4 things : it keep him hydrodynamically stable for the ride down, allows him to breath freely, offers excellent hook exposure for such a tiny hook, and encourages him to swim in circles. If you need to wash your hands or get a drink or something before fishing this bait, put your rod in the holder with the bait only 4or5 ft down so he can stay alive til you're 100% ready.
Once your ready send it all the way to the bottom at a pace your comfortable with, just be prepared when it hits bottom. Slow drops aren't too important for bait life, if you followed all the above steps 100%. If you have different rig, results will vary, but my rig keeps tangles to a bare minimum. If you hook your bait any other way, results will vary massively. Other than asphyxiation or squishing a bait up on deck, nothing kills them faster than a turbulent ride down through 180+ft of water. Back booked baits also drag water the wrong way over the gills. Cheek hooking keeps them straight and allows flow of water through their mouth. Personally, when working, I usually throw the clicker on and freespool it down in a rod holder, so I can still work while sending them. But you have to be ready right when you hit bottom. Usually there's not long to wait.
As soon as you hit bottom you want to force that perch to swim around right on bottom, but still feel a bite. In seas this can be tricky, as well as on a swinging boat. But the idea is that you move your rod up and down with the sea so that you always have bare tension with the weight remaining flat on bottom. This way the little perch is forced to swim in circles 10" or less from the bottom , staying in the visual range of a scamp peaking out of his scamp-hole but off the radar of aj and snapper. If you get a bite from a grouper, it's not a hard hit bit more of a grab and hold, when this happens don't swing, just slowly crank until you get tension loaded or not. Regardless, reel up after every bite. The bait needs to be alive. [Regardless what that old man told you, how many grouper did you witness him land with that technique?] Also only stay down about 5 minutes max, you'll have more bites than you feel. When you get to the top quickly inspect your bait. If it's still hooked right and frisky , send it back down immediately. If it's bit in half, you've likely got snapper problems. If it was a grouper, most likely it's just going to look dead for no reason on a quick look. A closer inspection will reveal that it was crushed probably most scales missing as well. If you bring up a bait like this, discard, rebait, and get back down immediately, in the same fishing spot.
Grouper don't like to wander much, and are very territorial. If you miss one you should try your hardest to get back down in the same spot fast, before the boat swings off spot. I've literally missed a grouper a half dozen times before finally getting him. If you get him, or go 15 min with no grouper bite, move up or down the rail 10-15 ft and try again. You pretty much have to drop your bait right in front of their hole to get bit. Thank goodness there's a lot of them down there!
Now all this is good and well unless the snapper hoard shows up. I usually wait and see what happens before even dropping, but if you've seen a half dozen red snapper in the first 5 minutes, it's probably a safe bet you are screwed. If you catch 3 reds in a row on your live bait,you're absolutely screwed, definitely wait until the next spot so you're not wasting bait, time, and arm strength dealing with reds. There are certain types of live bottom that typically have less snapper, but every day is different. Don't get mad at your captain if every drop is covered with snapper, I promise he's more frustrated than you about it, and doing his best to avoid it.