Natural Mortality Event For Fish In Rhode Island Draws Attention To Source Water Hypoxia

Despite alarm over numerous reports of dead fish in Rhode Island rivers, experts have assured consumers that they are not the result of water contamination.

“The DEM [Department of Environmental Management] told 12 News they received several reports of dead fish in the Providence and Seekonk rivers and have confirmed they were ‘natural mortality events’ of Atlantic menhaden,” WPRI 12 News reported. “DEM spokesperson Mike Healey said the phenomenon is known as ‘school-induced hypoxia’ — which means the concentration of oxygen within a school of fish changes.”

Hypoxia has been studied by marine scientists for decades and has caused hundreds of “dead zones” around the world. In Rhode Island, Healey attributed the recent surge in fish deaths to predators that were chasing the fish into shallow waters that don’t hold enough dissolved oxygen for them all. 

“It’s a phenomenon whereby oxygen concentration can vary with the structure and dynamics of a school of fish,” Healey told WJAR. “The dissolved oxygen (DO) of these waters is typically high this time of year, and with hundreds of thousands of fish in a small, localized section of shallow water, they can deplete DO in the immediate vicinity, which leads to some death.”

Unfortunately for local residents, this meant an influx of hungry visitors as well.

“It was like a scene from a movie,” according to a subsequent report from WPRI 12 News. “People stopped in their tracks to watch swarms of seagulls circling above Providence’s pedestrian bridge and diving into the river … It’s an all-you-can-eat buffet for black-backed and herring gulls as they go after a species of fish called menhaden.”

While mounting reports of dead fish and swarms of seagulls are far from pleasant, local consumers are likely relieved that there is a natural explanation for the phenomena, and they don’t seem to be the result of source water quality issues or contamination that might reach drinking water.

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