In the summer, when all the shrimp boats are out, i have seen the same exact thing. I was tacking out and noticed a huge area of disturbed water with birds EVERYWHERE. I was kind of curious so i just rode straight through it.Wow, just last week, I was kiting at dusk near a jetty, when about a mile out, I saw a whole mess of birds wheeling around, and decided to check it out. When I arrived, there were schools of baitfish breaking the surface and being snacked on by pelicans and seagulls, and I rode right through that mess.
As i approached, I realized it was kind of like a no turning back situation and i just went for it. I immediately regretted the decision, as i was going through the area, which was about 3 times bigger than it looked, I saw fins and fish just getting blitzed by huge fish and dolphins. I zipped past the bait ball and decided I should probably never do that again.
The water here is much different than S Fla so shark sightings are very rare until they are right on top of you or in the surf zone. Im sure the numbers are similar but what you cant see....
The only shark i have ever seen kiting was a few months ago. I was taking out and saw a 3-4 ft bonnet head just cruising ahead of me. As i approached, the thing just darted and disappeared.