How the Bonnet Carré opening is affecting our fish, crabs and oysters
For the first time in history, high water levels in the Mississippi River have forced the opening of the Bonnet Carre’ Spillway in consecutive years. More than half the gates on the St. Charles Parish spillway were opened on Feb. 27 to relieve pressure on the river levees. This was the third time in four years the gates have been opened, also a first since construction was completed in 1931.
These actions are necessary to try and prevent flooding of populated areas, but they do come at a cost to fisheries resources.
“It takes about two weeks for the water in Lake Pontchartrain to be replaced by water from the Mississippi River during a Bonnet Carre’ Spillway opening,” Louisiana Department of Wildlife and Fisheries biologist Carl Britt told us. “Saltwater gamefish species like spotted seatrout, red drum and black drum will be dislocated from Lake Pontchartrain in response to the introduction of such a large amount of fresh river water in a short period of time. These fish will move towards areas with higher salinity and where water is less turbid.”
Britt also said as for blue crabs, we should expect an initial dislocation, as well. However as they become acclimated to the lower salinity they tend to move back into the Lake to take advantage of nutrients and new food sources.
“A prolonged opening of the Spillway could cause mortality to oyster resources in Lake Borgne and the Mississippi Sound due to overexposure to fresh water and the potential for hypoxic conditions,” he said. “The continuation of fresh conditions could negatively impact the recruitment of juvenile brown shrimp into the estuary. A longer duration event also increases the possibility of algae blooms in Lake Pontchartrain.”
If water continues to rise?
Would there be more significant impacts if waters continue to rise and the Morganza Spillway has to be opened? How would that affect fisheries resources? We wouldn’t expect any additional impacts in the Pontchartrain Basin from an opening of the Morganza Spillway. You would likely have similar impacts in the Atchafalaya Basin that we are now experiencing in the Pontchartrain Basin.
River levels have raised concerns about whether the Corps of Engineers will have to open the Morganza Spillway in Pointe Coupee Parish as well. Any decision involving the Morganza will be made depending on how high and how fast the river is flowing. If that happened, it would have a negative impact on fisheries.
“You would likely have similar impacts in the Atchafalaya Basin that we are now experiencing in the Pontchartrain Basin,” Britt said. The Morganza Spillway was last used in May, 2011, when 17 gates were opened there in addition to the full capacity of the Bonnet Carre’ Spillway to try and control flooding.
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