Bottlenose dolphins live in the bays and passes around Naples and Marco Island all year, and they often ride the wake right next to the boat. Most tours last about 2 hours and also pass mangrove islands full of birds. Some add a stop on an island beach for shelling, and some run at sunset.
For the best chance of close sightings, pick a smaller boat. For the cheapest seat, pick a shared tour on a bigger boat.