Bottlenose Dolphins of the Lagoon — Sebastian, Florida

Common bottlenose dolphins live year round in the Indian River Lagoon off Sebastian, and they are among the most closely documented dolphins in Florida. FAU Harbor Branch Oceanographic Institute, based in Fort Pierce, began marine mammal research in 1996 with a National Marine Fisheries Service-authorized project to photo-identify and catalog every bottlenose dolphin in the Indian River Lagoon. Three decades later, that catalog covers the stretch of lagoon that runs past Sebastian and the Sebastian Inlet.

Researchers tell individual dolphins apart by their dorsal fins. According to FAU in 2024, each fin carries its own set of nicks, notches and scars, and the FAU Harbor Branch database includes more than 400 identified individuals from Sebastian to Jupiter Inlet. That work, together with a large 2016 to 2017 survey led by Hubbs-SeaWorld Research Institute, shows a population that is mostly resident, divided into local communities, and repeatedly affected by die-offs and human activity in the Indian River Lagoon.

Published estimates differ, and the sources give different figures. Hubbs-SeaWorld Research Institute reported in April 2021 that a team running 11 to 13 vessels along a 470 mile zig zag path covered nearly all of the Indian River Lagoon, conducted 135 surveys, analyzed over 150,000 images, and estimated an average of 1,032 dolphins residing in the lagoon. The peer-reviewed PLOS ONE study behind that release gives the range as 981 dolphins in winter to 1,078 in summer for the 2016 to 2017 survey year, and found that most Indian River Lagoon dolphins were resident to the estuary.

FAU Harbor Branch uses a higher round number. In a September 2024 article, FAU stated that about 2,000 dolphins live in the Indian River Lagoon, which it described as a 156-mile waterway along Florida's east coast. The two figures come from different organizations and methods: the 1,032 mean is a mark-recapture estimate for one survey year, while the FAU figure is a general statement, so neither replaces the other for the lagoon near Sebastian.

Most appear to stay close to home. An FAU Harbor Branch site fidelity study published in 2005 reported that between July 1996 and October 2001, 190 boat-based photo-identification surveys were carried out in the lagoon, with relatively high and consistent effort between 1998 and 2001 in a primary study area running from Sebastian Inlet in the north to Fort Pierce Inlet in the south. A total of 336 dolphins were photographically identified, and 149 of them were found in that Sebastian Inlet to Fort Pierce Inlet stretch.

Later FAU work describes neighborhoods. FAU reported in 2024 that Indian River Lagoon dolphins like to stay in certain areas, usually do not travel more than 30 miles from home, and form six dolphin communities across the lagoon. One example is a dolphin FAU calls STKR, which its Marine Mammal Stranding and Population Assessment team sighted frequently between Sebastian Inlet and Round Island Beach Park in Vero Beach, according to an August 2026 profile.

Not every lagoon dolphin belongs to the same group. The 2021 PLOS ONE study notes that genetic research suggests dolphins in the Mosquito Lagoon sub-basin, at the far northern end of the system, may be a disjunct community genetically distinct from the rest of the Indian River Lagoon. The same study defines its northern Indian River sub-basin as the lagoon north of the Eau Gallie Causeway, so the water off Sebastian falls in its southern Indian River sub-basin, which includes three of the lagoon's four inlets and, along with Mosquito Lagoon, has better water quality than the Banana River and northern Indian River.

FAU Harbor Branch runs the longest continuous effort. Its Stranding and Population Assessment team conducts monthly photo-identification surveys of cetaceans in the Indian River Lagoon and the Atlantic, according to a 2022 FAU profile, and works under a NOAA permit and a stranding agreement under the Marine Mammal Protection Act. A 2019 FAU thesis combined those monthly Harbor Branch relocations from 2003 to 2015 with fish and environmental data from the FWC Fisheries-Independent Monitoring program to study where Indian River Lagoon dolphins concentrate by wet and dry season.

Residents can contribute. FAU's Dolphin Spotter program asks shoreline observers to photograph dolphins and upload the images with time and place, which reaches canals and marinas outside the regular survey zones along the Indian River Lagoon. FAU reported in September 2024 that Dolphin Spotter sightings had been matched to 32 dolphins in the Harbor Branch database, out of 443 sightings submitted to that date, and that its rescue team had helped over 300 dolphins and whales.

The lagoon population has gone through several die-offs. NOAA Fisheries lists an Indian River Lagoon bottlenose dolphin unusual mortality event from May 2 to September 4, 2008, with 48 animals and an undetermined cause, and a larger one from January 9 to December 31, 2013, with 79 animals attributed to ecological factors. The 2021 PLOS ONE study counts Indian River Lagoon UMEs in 2001, 2008 and 2013, and states that at least 77 dolphins died in the 2013 event, about 7.5 percent of the population.

Those losses carry management weight. According to the PLOS ONE study, Indian River Lagoon dolphins are listed as a strategic stock because human-caused mortality likely exceeds the Potential Biological Removal level set by managers, the maximum number of non-natural deaths the stock can sustain annually. The study also notes that the northern Indian River and Banana River, with poor tidal flushing, were the common epicenter of earlier mortality events, farther north than Sebastian Inlet.

Bottlenose dolphins are protected under the Marine Mammal Protection Act. NOAA Fisheries asks the public to observe dolphins from at least 50 yards and limit viewing to 30 minutes or less, and lists illegal feeding and harassment, vessel strikes and fishing gear entanglement among the threats the species faces. Those threats are documented locally: FAU's August 2026 profile of STKR, the dolphin seen between Sebastian Inlet and Vero Beach, describes scars from a boat strike, and FAU notes that feeding dolphins is illegal and that dolphins comfortable around boats and fishing activity face higher risk of injury in the Indian River Lagoon.