Mississippi Department of Marine Resources says redfish, black drum and flounder could be displaced.
The Bonnet Carre Spillway and the Mississippi Sound.
This year’s spring rains and thaws from a hard winter have created the largest flood to come down the Mississippi and Ohio River valleys in a century. That led to the opening of the 5.7-mile long Bonnet Carre Spillway, which is located 32.8 river miles north of New Orleans.
The spillway has 350 20-foot wide bays, and was built after the Great Flood of 1927 to divert water from the Mississippi River into Lake Pontchartrain.
According to the U.S. Army Corps of Engineers New Orleans District Web site, the Bonnet Carre Spillway was partially opened on May 9, 2011, to keep the volume of the Mississippi River at New Orleans from exceeding 1.25 million cubic feet per second.
By the end of the day on Monday (May 17), a total of 330 bays were open and approximately 316,000 cfs of water was moving through the structure. The most bays that had been opened in recent history were in March of 1997 when 298 were opened briefly following the floods that year.
That is a lot of water.
In an extensive interview with the Mississippi Department of Marine Resources’ Deputy Director of the Office of Marine Fisheries Joel Jewell, Mississippi Sportsman asked the questions on the minds of Magnolia State outdoorsmen.
The bad news
The huge amount of freshwater coming through Lake Pontchartrain via the Rigolets and Chef Menteur Pass into Lake Borgne and the Mississippi Sound will form a wedge that will inundate the western part of the sound for several weeks.
“At a minimum, this will be devastating to the 12,000 to 14,000 acres of oyster reefs in the area,” Jewell said. “These oysters can take a few days of freshwater, but much more than that and we will see top-to-bottom destruction. The mortality can reach 100 percent.”
It is estimated that it will take two to four weeks after the Bonnet Carre is closed for the salinity to start reaching healing levels in the western sound.
Not only oysters will be at risk: This is a historic flood where warm rainwater runoff full of pesticides is replacing the normal cool melted snow water typical of spring river flooding.
Jewell said this “flushing effect” will displace juvenile gamefish populations of redfish and black drum, flounder and other fish that bed down in the reeds and estuaries of Hancock County. This will force these small fish out to sea or to the barrier islands, where they will be hard pressed to find suitable habitat to thrive.
“This will impact the food web of the sound for a long time, as these fish will be removed from the food chain and reproductive streams,” Jewell explained.
The absence of these small gamefish and the low salinity of the water during the inundation also will force all large finfish such as tuna, ling, snapper and tarpon well out to. Jewell advised that, most likely, the only large saltwater fish in the affected waters might be bull sharks, which traditionally tolerate brackish water.
The good news
The freshwater inundation will be isolated primarily to the western part of the Mississippi Sound, with the dividing line approximately at the Gulfport Shipping Channel, Jewell said.
In the Eastern Sound from Ship Island to Alabama, the effect will be minimal and fishing may actually be better than normal due to the flushing of species from Hancock County waters. Indeed, Round and Horn islands could house some of the best saltwater fishing this summer due to this event.
Jewell cautions Mississippi anglers not to write the coastal waters off altogether this summer. He admits oystermen, crabbers and inshore anglers, especially in Hancock County, will be hard pressed, but charter boats, deep-water fishermen and residents along the eastern Mississippi Sound should do well.
In addition, many freshwater fish will make a brief appearance along the sand beaches and inside barrier islands.
“In 1983 during a smaller flood, we have reports of bass being caught on the front beach in Bay St Louis, and we fully expect a repeat of this,” Jewell said.
A severe spring drought left salinities high in the sound for the crucial April to May growing season for larval shrimp, and the DMR is still confident of having a good to above average shrimp harvest, even in light of the flooding.
DMR officials have delayed the spring shell plant along Mississippi’s oyster beds, but will be ready when salinity increases enough to seed and transplant healthy oyster stocks into any habitat that has been compromised.
The lasting dangers
When asked about the long-term fears that the Office of Marine Fisheries has for south Mississippi from this event, Jewell said the main concern is the potential introduction of invasive species. Jewell said his office is actively monitoring “a half dozen to a dozen non-native invasive species that may now have a new avenue of approach to the Jourdan and Wolf River systems that has never been there before.”
These species include destructive Asian carp and zebra mussels that have infested Great Lakes and Mississippi River lakes for a generation. In recent years, these carp (known to some as “silver fin”) have proliferated and are found as far south as Louisiana. Jewell worries that Mississippi may be next on the list.
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