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Climate change hurts Louisiana’s oysters and shrimp

By; Susan Buchanan

Greater New Orleans is expected to be even hotter ten years from now. And the impacts of climate change on local seafood production will grow. Scientists in Louisiana say these changes could reduce supplies of fresh oysters and shrimp.

Julie Lively, associate professor and fisheries specialist at Louisiana State University AgCenter and Louisiana Sea Grant, said in the short term, more severe weather could negatively impact shrimp and oysters because of their dependence on temperatures and water salinity.

Louisiana accounts for over a third of the nation’s oyster output and well over a third of its shrimp landings. The state’s oysters have partly recovered from a hit they took after the BP spill in 2010. Shrimp landings are down, however, Climate change has already affected south Louisiana’s seafood, Earl Melancon, emeritus professor of biological sciences at Nicholls State University in Thibodaux, said. Sea level rise, higher atmospheric temperatures and sudden changes in the thermometer, along with hurricane intensity, increased bouts of heavy rain – and the opposite, greater droughts – will become more pronounced.

Environmental parameters work in combination with one another and have real consequences for seafood production, Melancon said. As changes in weather become more extreme and less predictable, they may one day create a tipping point, or an unstoppable situation, for commercial seafood, he said. Plaquemines Parish, with its fleet of vessels and fishers, is ground zero for the ways that climate impacts the biology, ecology and economics of shrimp and oyster production, he said. That’s of interest in New Orleans, where plates brim with Plaquemines seafood.

Oysters are immobile after a two-week, swimming larval stage, Melancon said. Once they settle on the bottom, they’re dependent on water currents to bring them food for filtering and waste removal and to disperse their larvae during spawning. Wetlands loss changes water currents and dramatically alters the ability of reefs to sustain oysters. Soil no longer binds, and sediment can bury and suffocate a reef.

Lively at LSU said continued subsidence with sea level rise can cause additional land loss. “Shrimp thrive with our marsh edge, but as more of it sinks, there’s less habitat,” she said “This can lead to salinity changes, which oysters can only tolerate in small changes. Shrimp populations may move based on salinity and temperature changes, but oysters can’t just move.”

So, what about rising and changeable temperatures? Water temperatures are a driving force for shrimp movement out of marshes and shallow waters into deeper bays and the Gulf, Melancon said. As water temperatures rise, shrimp growth rates may increase. But with an earlier warming, the spring brown shrimp will be forced into deeper, cooler bays and Gulf waters before they reach commercial sizes.

Cold fronts will be less predictable in the future, he said. Cooler, earlier low-water temperatures will force juvenile, fall white shrimp into deeper, warmer bays and Gulf waters before they reach commercial sizes.

Oysters have two spawning peaks in Louisiana and other Gulf states. Oysters mature and spawn based on rising water temperatures in the late spring and early summer, and spawn again in declining water temperatures in the fall and early winter. “As weather and temperatures become more random and unpredictable, we’re seeing changes in spawning patterns of oysters, with one or both spawning peaks often lost or severely diminished,” Melancon said.

Morgan Kelly, assistant professor of biological sciences at Louisiana State University, said, “From our research on oysters, I can tell you that warming temperatures from climate change are likely to exaggerate the negative effects of fresh water.” Oysters have a “sweet spot” at about 15 parts per thousand salinity, which translates to about one-half freshwater and one-half seawater. Too much freshwater and oysters will close up and stop feeding, she said. On the other hand, too much saltwater, and they’re more susceptible to diseases and predators.

As local seafood supplies shrink, consumers will look for alternatives. “Farmed is replacing wild caught, and the majority of it’s from Asia—Indonesia, China, India, Vietnam and other countries,” Julie Lively said. As it is, over 90 percent of shrimp consumed in the United States is imported now, with most of it produced by farming.

Susan Buchanan is a Contributing Writer for The Louisiana Weekly.