You might not want to rely on spotting dolphins to make you safe. Birds and dolphins both can be indicators of risk because they are after the baitfish. Same as the sharks that ply those waters in close (tiger, bull, etc). Also, avoid wearing shiny sparkly things (rings, jewelry, or accents on your swimwear) because they look like fish reflecting light underwater to predators.
Same idea with sharply contrasting colors on a swimsuit. If the water is murky then predators can't see as well what they are attacking. In the surf you might be bitten by complete mistake b/c you aren't seen clearly.
And yes, avoid anywhere where fishing or chum is in the water, and piers (fishing often occurs off of piers, and crabbing, plus the currents can be different around piers, too).
It really isn't rocket science, just google what NOT to do. But it isn't any guarantee, either. You're in their environment in the water. Period. Stay in under 2 feet of water or on the sand if you want to be sure. If you are willing to take on calculated risks, follow the above and don't splash around like a school of fish...