In a hidden pocket of Tampa Bay mangrove forest, Steve Murawski's team of scientists caught a Centropomus undecimalis, the common snook. At 22 inches and with a jet-black line running horizontally across its body, the snook was the 681st fish caught by the Tampa Bay Surveillance Project, a sweeping research initiative that aims to study contaminants found in the bay's most coveted fish species: spotted seatrout, redfish, sheepshead and snook. Fish No. 682 came minutes later, also a snook.

A handful of the region's top recreational fishing charter captains have partnered with scientists from the University of South Florida's College of Marine Science in St. Petersburg for the five-year study to catch and sample the popular species along the shores of the estuary's 400 square miles.

Researchers are focusing on the inshore fish most commonly caught for food, Murawski said, which is why studying their chemistry is so crucial. After scientists reel in a catch, they bring them ashore to test the fish in the university's lab for a cocktail of contaminants, including pesticides, pharmaceuticals, a durable group of slow-to-break-down "forever chemicals" and more.

"Tampa Bay is one of the fishing hotspots of western Florida and the Gulf, so if there are any threats to consuming these fish, it's important for us to know about them," said Murawski, a professor of oceanography at the College of Marine Science and the project's principal investigator.

"The animals that we're catching are top predators," Murawski said. "But the ultimate top predator is people. Are these chemicals being transferred at higher and higher levels of concentration? We think that's true."

Not only are researchers testing fish for pollutants, they also want to learn whether the people who fish in Tampa Bay for food are more at risk of contamination. A three-year survey of people in the region who fish for food should shed light on seafood-eating habits and help scientists come up with risk assessments for safer consumption, according to the project.

Matt Santiago, 41, has been fishing in the bay since he could walk, and he regularly eats the fish he catches. That's why the professional charter captain of more than 17 years happily agreed to help the university's researchers determine what's fouling fish.

"Our industry is heavily dependent on the sustainability of our natural resources. We need to take good care of our water," Santiago said. "The more information that we can gather about these chemicals, the better. It's a really important thing."

Plus, the project's results could help local governments pinpoint where the bay's pollution is coming from.

For instance, if a redfish caught in northern Tampa Bay has more pharmaceuticals, like opioids, in its system than a redfish caught in the bay's southern end, that could signal there is a wastewater pollution problem in the northern bay. It's difficult for treatment plants to filter out trace amounts of pharmaceuticals, so when humans urinate chemicals from the pills they ingest, that can ultimately end up in the bay.

Or perhaps a sheepshead, with its iconic black-and-white bars, is caught near a part of the estuary with a heavy agriculture footprint. The presence of pesticides in that fish could tell officials that more needs to be done to control rainfall runoff from area farms.

"This is not just a bellwether, it's the largest open-water estuary in Florida," Murawski said. "We ought to understand this pretty well... If we can help identify the source of some of these pollutants, it helps."