News & Resolutions

Fish Kills Reported in Isaac's Wake

September 14, 2012 12:00 AM

Reports of fish kills in the wake of Hurricane Isaac have been pouring in from across southeast and central Louisiana since the storm brought its high winds, torrential rains and flooding storm surges throughout the last week of August. The most devastating kills have been observed in the Lake Verret Basin, a broad area of shallow swamps, bayous and lakes near the towns of Morgan City and Pierre Part, about an hour southwest of Baton Rouge. Also impacted is the upper Barataria Basin, just minutes west of New Orleans and site of record-setting bass catches during the 2011 Bassmaster Classic tournament.

Smaller fish kills have been reported along the north shore of Lake Pontchartrain and around Lake Maurepas between Baton Rouge and New Orleans.

Forage fish like shad and small sunfish are generally hardest hit. However, that doesn’t mean popular gamefish like largemouth bass and crappie (known locally as sac-a-lait) and commercial and sportfish species like channel catfish are spared.

The obvious culprit for the kills is the saltwater storm surge brought in by nearly a week of relentless, powerful southeast winds that inundated freshwater and brackish swamps both east and west of the Mississippi River. Freshwater fish like bass and bluegill simply cannot get away from the surge fast enough and succumb to the high salinity.

But increased salinity level isn’t the only culprit. The primary cause of the die-offs is same reason Louisiana’s vast array of shallow lakes, swamps and bayous are so tremendously productive in the first place.

These swamps contain an incredible amount of decaying materials like fallen leaves, trees, dead aquatic vegetation and dead animals. This provides an enormous amount of nutrients and feeds the food chain during stable weather. Microorganisms eat the nutrients. Small fish, crawfish, grass shrimp and other invertebrates eat the microorganisms. Then the bigger fish like bass, catfish and bluegill eat the small fish and crawfish.

That rich organic mixture can turn deadly when a hurricane makes landfall. High wave action caused by hurricane winds, rain runoff from interior swamps and currents from increased tidal flows stir up the decaying materials, dramatically increasing the amount of nutrients suspended in the water. After the hurricane passes and the waters heat up, a tremendous amount of decay takes place at once and can spawn algae blooms that suck the dissolved oxygen out of the water and increase bacteria levels.

The fish trapped in the oxygen depleted water are forced to the surface to try to breathe air and generally begin dying quickly.

It’s a process south Louisiana has seen many times in the last 20 years in the wake of Hurricanes Andrew, Katrina, Gustav and now Isaac.

The most devastating die-offs came after Andrew in 1992 and Gustav in 2008, both strong storms that took direct paths across the Atchafalaya Basin. Surveys conducted in the weeks after both storms found miles-long stretches of bayous and canals in the Atchafalaya and Lake Verret where nearly every fish had died.

Fortunately, floods in the Mississippi River basin the following winters and springs brought oxygen-rich water into the Atchafalaya, flushing the dead water out and rejuvenating the area. And local anglers worked with state fisheries biologists to help restock fish and bring incredible fishing back within two years of the massive fish kills.

This connection to the Mississippi River gives the Atchafalaya Basin new blood each spring and will also help fish populations in the upper Barataria Basin and the Delacroix area affected by Isaac. Both areas’ freshwater and brackish marshes were inundated with storm surge. But because of the Davis Pond and Caernarvon freshwater diversion projects, which carry water from the river through levees and into wetlands, freshwater fish populations could rebound in these areas in as little as a year.

Isaac’s impacts don’t appear to be nearly as widespread as Andrew’s and Gustav’s, but unfortunately come just two years after tremendous fishing returned to the Atchafalaya and Lake Verret area in Gustav’s wake.

Anglers and wildlife agents stand ready to help this time around as well and anxiously await a slug of fresh, oxygen-rich water that will hopefully come from the Mississippi this upcoming winter and early spring.


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