Charleston Harbor shelters more than 300 Atlantic bottlenose dolphins year-round, the largest resident coastal population between Cape Hatteras and the Florida Keys. The estuary's 450 square miles of tidal marsh and creek networks create a brackish nursery where juvenile dolphins learn cooperative fish-herding techniques from older pod members, behavior documented continuously since the South Carolina Marine Mammal Stranding Program began tagging individuals in 1992. The harbor's shipping channel, dredged to 52 feet in 2004, altered longstanding feeding patterns, and marine biologists now track seasonal movements through a photo-identification catalog numbering more than 840 individual dorsal fins. The Charleston dolphin tour industry emerged in the early 1980s when commercial shrimpers began carrying passengers between Fort Sumter runs. Today's operators follow federal Marine Mammal Protection Act guidelines that mandate 50-yard standoff distances and prohibit chasing or encircling pods. Morning departures align with the incoming tide, when dolphins drive schools of menhaden and mullet into shallow creeks along the marsh edge. Captains communicate sightings by VHF radio, a practice that concentrates vessels near active pods but allows naturalists aboard each boat to observe behaviors like tail-slapping, breaching, and strand feeding — a rare technique in which dolphins beach themselves momentarily to trap fish on mudbanks. The harbor's military history shares the water with its marine ecology. Tour routes pass Fort Sumter, where the Civil War's opening shots were fired in April 1861, and Castle Pinckney, a decommissioned seawall battery on Shutes Folly Island. Tall ship operators combine dolphin spotting with sailing instruction on gaff-rigged schooners modeled after 18th-century coastal traders. Sunset cruises depart at 18:30 from May through September, timing the return leg to coincide with the evening feeding surge as baitfish rise toward the surface. The Cooper River and Wando River confluences create nutrient upwellings that sustain the estuary's biomass, and the dolphins' presence serves as a real-time indicator of water quality and forage fish abundance, metrics monitored by the South Carolina Department of Natural Resources through quarterly acoustic surveys.