Gulf of Mexico
Bonnet Carré Spillway - Wikipedia

Did opening the Bonnet Carré kill dolphins, turtles in Gulf? Mississippi, Louisiana officials disagree

Mississippi authorities are blaming the Bonnet Carré spillway for the dead dolphins and turtles washing up on their shore, though Louisiana officials are contesting those claims, and federal scientists are withholding judgment until they know more.

The U.S. Army Corps of Engineers is increasingly reliant on opening the spillway to divert high water from the Mississippi River toward Lake Pontchartrain to prevent flooding around New Orleans. The Corps has opened the gates in three of the last four years, including a 43-day stint that concluded earlier this month.

The Corps did not respond Tuesday to requests seeking comment. Louisiana Wildlife and Fisheries staff said they haven't heard of any efforts to change how the Bonnet Carré is managed; the decision to open its bays is based on Mississippi River water levels.
But allowing so much fresh water to drain into the Mississippi Sound is hurting wildlife, said Moby Solangi, director of the Institute for Marine Mammal Studies in Gulfport, Mississippi. He estimates that so far this month his group has encountered 25 dead Kemp's ridley sea turtles, an endangered species.

The IMMS will also perform necropsies on dead dolphins that have washed ashore; 45 have been found in Mississippi so far this year, said Erin Fougeres, administrator of the marine mammal stranding program for the National Oceanic and Atmospheric Administration's regional office.

Mississippi averages 32 strandings — including dead animals — between January and April, and while the number this year is up, it hasn't risen high enough to prompt an official federal investigation, Fougeres said. Her office is keeping an eye on the situation but Fougeres is reserving judgment until all the veterinary results are in, which could take weeks or months.

Corps of Engineers completes closure of Bonnet Carre Spillway, 43 days after it opened

Corps of Engineers completes closure of Bonnet Carre Spillway, 43 days after it opened

Louisiana officials, meanwhile, have said that opening the spillway can hurt oysters and slow growth of shrimp, but that larger, more mobile animals can simply swim away.

In a way, allowing Mississippi River water to spill over toward Lake Pontchartrain mimics how the river would have behaved before the levees were built, said Martin O'Connell, director of the Nekton Research Laboratory at the University of New Orleans.

Fougeres explained how freshwater intrusion could potentially hurt animals like the bottlenose dolphins that live off the Mississippi coast: When salinity drops, it affects the animals at a cellular level. Skin cells can't regulate the amount of fluid inside them. They balloon up and deteriorate, allowing bacteria and fungi in, where they can cause infections and lesions. Dolphins stick to their home territory and are reluctant to move, even when faced with destruction, as evidenced last year off the Gulf coast of Florida where many died during a red tide outbreak.

Too much fresh water can also damage the animals' eyes and alter their blood chemistry, but the lesions are a clue that fresh water is affecting them. Several of the dolphin carcasses that have been examined showed lesions, and others were too decomposed to tell one way or the other, Fougeres said.

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Corps of Engineers completes closure of Bonnet Carre Spillway, 43 days after it opened