I have to assume that when you say "Shiners" you're talking saltwater baitfish (there are shiners in freshwater too but they're a specific species). If you're here in Florida, baitfish can mean that you're talking about whitebait, pinfish, threadfins or other baitfish. As far as finding bait, in Longboat key there as an area around Jewfish key - in approx 3 to 4 feet of water - that is a excellent place to catch scaled sardines, pinfish and more.
Attracing Bait: I would suggest using Purina Tropical Fish Food to chum all your baitfish. It comes in powder form. Most tackle shops and feed stores should have it. If you can not find Purina Tropical Fish Food, you can use Jack Mackerel mixed with instant mashed potatoes or oatmeal.
If you are not familiar with using a castnet (it takes practice but is the move effective way to get a day's worth of bait in a short period of time) you can catch bait with a lure combination called a Sabiki rig.
Finding baits anywhere.
Although the image we showed you is specific to where you're fishing, remember the conditions that result in bait showing up there. And in the deeper water next to where the bait is there are often bigger fish waiting to eat them. From grouper in the deeper channels near the Gulf to shallow(er) areas near almost any pass or opening, there are big fish where there are little fish.
You will find spots like this anywhere on both coasts of Florida - West or East, and onto the Panhandle and down to the keys. Shallow areas hold the "shiners" you are looking for, and the more water flow there is the more likely you will find the bait. This image is from Tarpon Springs, where we fish a lot of the time. You can see very similar passes up and down the outislands to the left.
Let us know how you do.
Captain David M Rieumont
You can check out Captain David himself from his incredible and very popular Patriotic Angler podcasts. They cover every bit of fishing you can imagine, and there are new ones being created constantly. David and his team remain one of best resources any fishing community has anywhere in the country.