Freshwater intrusion from the Bonnet Carre spillway is damaging aquatic life in the Mississippi Sound, with 13 dead dolphins and 23 dead sea turtles found along the Mississippi Coast in the last two weeks.
The carcasses are being necropsied by Mississippi State University veterinarians at the Institute for Marine Mammal Studies in Gulfport. Executive Director Moby Solangi said the verdict is still out on the causes of death, but both the turtles and dolphins have skin and eye lesions consistent with freshwater damage.
Solangi said 22 of the dead sea turtles are endangered Kemp’s ridleys, while two baby dolphins are among the most recent dolphin carcasses retrieved. Carcasses are being found in all three coastal counties, he said.
Solangi said a total of 40 dolphins have been found dead so far in 2019.
The Mississippi Department of Marine Resources also confirms the fresh water is damaging oyster reefs, particularly in the western Mississippi Sound.
‘You have a hurricane’
The U.S. Army Corps of Engineers opened the spillway for 44 days to protect New Orleans and other communities from Mississippi River flooding. Up to 210 cubic feet per second of fresh water poured through the spillway gates.
“When you get a big slug of wind and water, you have a hurricane,” Solangi said. “When you get a big slug of fresh water, it changes the habitat and it’s going to take a long time to recover.”
“ . . . It’s a flood, like it or not, it’s a flood of freshwater coming in. It’s been coming in for two months continuously. All the living organisms, even the plant materials, are affected.”
The Mississippi Sound’s oyster fishery suffered “severe economic hardship” from the opening of the Bonnet Carre spillway for 48 days in 2011, according to a report from Mississippi State University.
After the 2011 freshwater intrusion, the DMR oversaw replenishment of about 1,000 acres of oyster reefs in the Mississippi Sound, said Joe Jewell, DMR’s director of marine fisheries.
A $10 million grant replenished those beds and helped sea turtles recover. Funding included pay for fishermen who helped with the project and otherwise would have been out of work because of the decimated oyster beds.
Jewell said the impact of the fresh water did not end with closing of the gates on April 9. This year marked the 13th time in 90 years the spillway has been opened, The New Orleans Advocate reported.
Although the spillway has closed, “the event,” as Jewell refers to it, is not over.
“It takes two to three weeks, sometimes more, for all that freshwater to flush out,” he said.
“We are seeing some significant mortality — upwards of 50 percent — with the smaller oysters. The larger oysters appear to do a lot better.”