Posted: 20 Jun 2011 06:01 AM PDT
By Veronica Del Bianco and Alice Bumgarner
This spring the Mississippi River made headlines as the river reached historic crest levels. By way of natural and manmade channels, freshwater gushed into Louisiana estuaries, threatening the lives of productive Louisiana oyster beds.
But does the freshwater threaten oysters' long-term survival as a species? Despite a bad prognosis for some oysters, seafood industry leaders explain that harvesting grounds are vast and oysters continue to be sustainably harvested, which bodes well for the long term.
"We could see 100 percent mortality in some of these areas," biologist Patrick Banks told the Times-Picayune, referring to the estuaries and coastal waters of Louisiana.
Banks is in charge of the oyster program for the Louisiana Department of Wildlife and Fisheries (LDWF). He tells the Times-Picayune that every time freshwater has been pushed into the estuaries, the impact is different, depending on the quantity of freshwater and at what stage of the oysters' life cycle it arrives.
In this case, the quantity is significant. At the height of the Mississippi River flooding, the Morganza Spillway discharged 114,000 cubic feet per second for five days. That's in addition to the Bonnet Carre Spillway, which since May 18 has had 330 of its 350 bays open.
Freshwater: Friend or Foe?
To understand why the extra freshwater threatens to have such a negative impact on the humble oyster, one must take a brief lesson in the biology of the mollusk.
Oyster blood needs to stay in "osmotic equilibrium," explains Dr. Bryan P. Piazza of The Nature Conservancy. When the water trying to enter an oyster has a lower salinity than what's inside, the mollusk literally tries to "clam up" in order to maintain its delicate balance, constricting its valve or even shutting its shell tight.
If this occurs, the oyster can't filter water or feed effectively, and gas exchange is compromised. Basically, the oyster starves.
Making survival more difficult is the fact that, in this case, the arrival of freshwater coincided with the higher temperatures of summer. When temperatures are high, oysters need to feed more than usual. If they've clammed up to maintain equilibrium, they can starve at an even faster rate.
Piazza underscores that oysters do need some freshwater. "Freshwater is not the enemy," he says.
Floods from the freshwater rivers are what helped Louisiana's rich oyster beds develop in the first place, says Banks. Floods are a natural part of the cycle.
Unlike other species with mobility, however, oysters can't move when their environment becomes too extreme for survival.
2 Million Acres of Reefs to Work With
Banks's and Piazza's prognosis may sound doomsday-ish, until you remember that Louisiana has around two million acres of oyster-harvesting grounds to work with.
"Our harvest will be reduced some because of the floods, but two million acres of oyster-harvesting grounds in Louisiana will be able to provide oysters for buyers, without any risk of overfishing," says Greg Voisin, director of marketing and sales for oyster-processing company Motivatit Seafoods.
Tasked with ensuring that oysters aren't overfished, the Louisiana Department of Wildlife and Fisheries and the state's Department of Natural Resources regularly sample and monitor the 1.5 acres of oyster reefs owned by the state.
"They've closed areas when they've felt like they needed to be closed for spawning," says Voisin.
The other half-million acres of oyster reefs are privately owned and are neither monitored nor certified by the state. Even so, says Voisin, the economics of oyster harvesting practically ensure that the reefs are sustainably harvested.
Harvesting With Sustainability in Mind
Oysters are typically left in the water until they're at least three inches long, he explains, because there's no market for them. That means the younger oysters are left intact. That gives them time to reach the age of spawning, which occurs twice a year, when the water drops to 70 degrees.
"If you brought two-inch oysters into a shucking house, they'd tell you to turn your truck around," says Voisin. Oysters that small are "almost humanly impossible" to open. Besides, he says, shuckers get paid by the sack. Why shuck 600 small oysters when you could shuck 280 big ones for the same pay?
People may have the impression that, after the natural and manmade disasters of the past few years, oyster beds are being perilously overfished. But that isn't the case, he says.
Each oyster of spawning age can lay up to one million eggs a year. "We obviously don't get 100 percent of that yield," he says. "If they spawn even three percent of that, we have more oysters than we know what to do with."
As the seventh generation of Voisins to work in Louisiana's seafood industry, Greg puts a premium on managing the coast's natural resources wisely. After Hurricane Katrina, he and other seafood industry workers spent countless hours pulling away trash from the reefs that the turbulent ocean had washed up.
"If we don't have healthy reefs, we go out of business," he says. "We're the biggest environmentalists out there."