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Are fishermen right? Is a cleaner Narragansett Bay killing winter flounder?

One of the few remaining lobstermen who still work the Bay, likened the bottom to Chernobyl — a dead zone. Scientists believe it's climate change.

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PROVIDENCE — Ever since the first Europeans arrived in what would become Rhode Island, its lands and waters have been primed for change. 

The early settlers razed forests to make way for farms. Their descendants dammed rivers to power mills. They filled the Great Salt Cove in Providence and marshes all around Narragansett Bay. And soon, they started pumping sewage and wastewater laced with contaminants into its waters.  

The impacts were felt across ecosystems. Bird and animal life changed as more fields and scrubby edge habitats were carved out of woodlands. Atlantic salmon, blocked from spawning grounds by river barricades, disappeared, while herring and shad numbers plummeted.  

Fueled by nutrients discharged into the Bay by a rapidly industrializing Providence, farmed oyster beds thrived around the turn of the 20th century. But pollution eventually caught up. Beset by disease, the industry crashed. Further south, in Greenwich Bay, something similar would happen to once-rich scallop beds as underwater meadows of eelgrass died out. 

Passage of the federal Clean Water Act in 1972 started a slow process to cut down on pollution and nutrients flowing into the Bay. The work accelerated more recently, largely due to a devastating fish kill in Greenwich Bay in 2003 that was tied to nutrient discharges.

Elements like phosphorus and nitrogen can fuel the excessive growth of phytoplankton. When the tiny marine plants die off in high enough quantities, they sink to the bottom of the water column, decompose, and deplete oxygen levels to the point that fish and other organisms can no longer survive.

In the wake of the incident, wastewater treatment plants were forced to adopt strict controls on the amounts of nitrogen in their effluent. Levels that had been going up steadily since the late 19th century before leveling off in the 1960s were sharply curtailed. From about 2005 to 2015, they plummeted by more than 50%.

Fishermen have complained since then that the Bay has become too clean. They argue that government regulators have essentially cut off the supply of fertilizer to the Bay, that there aren’t enough tiny marine plants anymore to drift down and feed the inhabitants at the very bottom, which means that species like winter flounder or lobster end up suffering.

Their contention picked up enough momentum that the Graduate School of Oceanography at the University of Rhode Island devoted a day-long conference to the issue a few years ago. In one session, Al Eagles, one of the few remaining lobstermen who still work the Bay, likened the bottom to Chernobyl — a dead zone. 

Scientists counter that the declines of winter flounder and lobster in the Bay predate the most recent nutrient reductions and have found convincing evidence that the two species, both adapted to cold waters, are losing out primarily because of temperature increases tied to climate change. A winter-spring bloom of phytoplankton that is critical to bottom-dwelling species has also been declining over decades because of warming waters, they say.

Could fewer nutrients be playing a part?

Could fewer nutrients be playing a part?

Before the Industrial Revolution drove the rapid urbanization around upper Narragansett Bay, nutrients were coming into the Bay through natural processes: erosion, storms and, in large part, ocean currents. 

The late URI oceanographer Scott Nixon determined that amounts were about a fifth of what they were in the late 20th Century, and yet there are records and anecdotal evidence of healthy stocks of winter flounder, lobster and other bottom-dwelling fish and shellfish in the Bay. Even with the recent reductions, nutrient levels are still well above what they used to be.

“We’re still not back to pre-industrial levels of nutrients,” says Candace Oviatt, professor of oceanography at URI. “It’s still high and still dominated by wastewater treatment plants.”

She looked at differences in fish numbers in the Bay over a period from the 2000s to the 2010s and determined that total biomass may have dropped by about 10%, but she said the results are not definitive and the driver is unclear. 

A more comprehensive study of nutrient impacts over a longer period of time is underway by other scientists at URI.

Before the stricter rules were enacted, Nixon described the effort to wean the Bay off nitrogen as an “ecological adventure” that may have unintended consequences. It may still be too early to draw conclusions about the full impacts on the ecosystem.

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