Sarasota Bay Dolphins May Swallow More Than 10,000 Microplastic Particles a Day Through the Fish They Eat, Study Finds

Bottlenose dolphins that live year-round in Sarasota Bay may be swallowing more than 10,000 microplastic particles a day from just two of the fish they eat, according to a study published this year in the journal Marine Mammal Science. Researchers working with the Sarasota Dolphin Research Program found microplastics in about 83 percent of the dolphins they sampled and in nearly every pinfish and Gulf toadfish, two staples of the dolphins' diet.

Whether those particles are harming the dolphins is still unknown, the researchers said. But the close match between the plastic found in the fish and the plastic found in the dolphins suggests the particles are moving up Sarasota Bay's food web, from small fish to one of the region's best-known predators.

What the study found

The paper, titled "Microplastic Munchies: Exploring Microplastic Trophic Transfer Potential Between Two Key Prey Fish Species and Resident Common Bottlenose Dolphins (Tursiops truncatus) in Sarasota Bay, Florida," was published online May 15 and appeared in the journal's July 2026 issue. Its authors include Randy Wells, who directed the Sarasota Dolphin Research Program at the time, and about a dozen other researchers, WGCU reported on Nov. 9.

The team compared particles found in 23 free-ranging dolphins with those in 35 pinfish and 30 Gulf toadfish caught in the bay. According to the journal listing, it was the first study to use both gastric and fecal samples from free-ranging dolphins to look at microplastics. The share of samples containing particles was high across all three species, according to the paper's abstract:

Fibers were the most common shape in all three species. Pinfish carried more plastic than toadfish, with a median of 1.4 particles per gram of tissue compared with 0.6 particles per gram, a statistically significant difference.

Using estimates of how much a dolphin eats each day and how much of its diet is made up of these two fish, the researchers calculated that Sarasota dolphins may take in more than 10,000 particles a day from pinfish and toadfish alone. Because the figure counts only two prey species, it is not a total for everything a dolphin eats.

Why the researchers think the plastic comes from prey

The microfibers in the dolphins were largely the same shapes, sizes and mix of colors as those in the pinfish and toadfish, WGCU reported. The authors wrote that "the extensive overlap observed in particle shapes, colors, sizes, and polymers across species" points to trophic transfer, the movement of a contaminant from prey to predator.

The researchers stopped short of proving it. Testing the idea directly would have meant feeding dolphins fish known to be loaded with plastic, which would be unethical, WGCU reported. Dolphins could also be taking in particles by breathing them or by swallowing water while they feed.

Earlier work has found similar microplastics in nine other baitfish species common in the dolphins' diet, according to WGCU. A 2024 study in the journal Environments screened muscle and gut tissue from 11 species of dolphin prey fish caught in Sarasota Bay and found suspected microplastics in 82 percent of muscle samples and 97 percent of gut samples. Pinfish had the highest levels in both tissues in that study as well.

From foam to clothing fibers

Earlier research in Sarasota Bay found tiny bits of plastic foam, the material in foam cups and takeout containers, in dolphins. The new study found mostly fibers of the kind shed by clothing, WGCU reported.

The researchers suggested the shift might be linked to the City of Sarasota's restrictions on polystyrene foam. City commissioners voted unanimously on Aug. 19, 2019, to bar foam food containers on city-owned property, including sidewalk cafes, special events and businesses that lease city land. The rules took effect in stages, starting with sidewalk cafes on Jan. 1, 2020, according to local reports at the time.

The likely source of the fibers is wastewater from washing machines, the researchers said, according to WGCU. Many of the fibers are too small for most wastewater treatment plants to filter out, so they can pass through and into coastal waters.

What the particles could do

Microplastics could affect dolphins in several ways, according to WGCU. The particles can make an animal feel full when it still needs food. They can scratch or damage the digestive tract and cause inflammation and cell damage. Some plastics also leach hazardous chemicals.

Sarasota Bay dolphins have already shown exposure to such chemicals. A 2022 study in Frontiers in Marine Science noted earlier findings of widespread exposure to phthalates, chemicals used to make plastics flexible, in the bay's dolphins. That same study, led by researchers at the College of Charleston, found suspected microplastics in gastric fluid from all seven dolphins sampled in 2019, and its authors described it as the first screening for ingested microplastics in free-ranging bottlenose dolphins. A later study found microplastic particles in the exhaled breath of all 11 dolphins tested in Sarasota Bay and Barataria Bay, Louisiana.

The paper's authors wrote that "this study highlights the need for further research on how microplastics travel through marine food webs" and on what the particles mean for the health of the animals that eat them.

Why Sarasota Bay's dolphins matter

The Sarasota Dolphin Research Program, a program of Brookfield Zoo Chicago based at Mote Marine Laboratory and Aquarium, runs what it calls the longest-running study of a wild dolphin population in the world. Its work in Sarasota Bay began in October 1970, and it has documented six generations of the bay's resident dolphins, including the oldest wild dolphin known, which lived to 67.

Because the same dolphins stay in the bay throughout their lives and are examined during regular catch-and-release health assessments, researchers can track how pollution in one Florida estuary shows up in a long-lived predator. The earlier fish study also examined muscle tissue, the part people eat, and its authors framed the results as relevant to seafood consumers as well as to predators like dolphins.

What's next

The authors called for more research on how microplastics move through marine food webs and what they do to the animals that consume them. For now, the researchers can say the dolphins are taking in plastic, and likely through their food, but not yet what it is doing to them.