Low seafood catches remain a mystery
Seafood catch numbers and conventional wisdom among shrimpers, crabbers, oystermen and fishermen suggests that the poor haul of seafood coincided with the BP oil spill of 2010, which leaked an estimated 4.9 million barrels of oil into the Gulf of Mexico.
But scientists say it isn’t so simple to establish a cause-and-effect connection, since for nearly every species of seafood affected, there is an alternate narrative that explains the landings.
“As scientists, it’s hard for us to speculate because there’s such a high standard. We hold out on what claims we make,” said Scott Porter, a scientist at the Louisiana Universities Marine Consortium research center in Cocodrie. Porter also works as a researcher and diver at the nonprofit EcoRigs, which converts retired oil platforms for sustainable seafood fisheries.
“My studies of oysters since the spill have been trying to find a direct link,” he said. “That hasn’t been extremely easy. Oysters are pretty tough organisms; that’s why they live in the environment they do. It takes a lot to kill them.”
The low oyster harvest can be attributed to several causes other than the oil spill itself, such as the state’s freshwater-diversion program, which opened Mississippi River floodgates in an effort to prevent the leaking oil from invading sensitive inland marshes.
In 2011, the opening of the Morganza Spillway to keep the Mississippi River from flooding into urban areas again exposed oysters, which rely on high salt content in the water, to fresh water.
Porter said he collected oysters from Breton Sound in September 2011, shucked them and put them under a UV light that was set to pick up on certain hydrocarbons.
“The discussion was how come there’s mortality in the oysters,” he said. “They fluoresced the same color a fresh tar ball did.”
Porter then sent the samples to a laboratory. The results indicated the oysters’ tissue contained 200 parts per million of total petroleum hydrocarbons and 31 parts per million of diesel.
“That is significant in the oysters,” said Porter, “so the question is anyone looking at the crabs and the shrimp this way?”
Scott Killian, who works with Porter at EcoRigs, cited another unpublished study they have conducted, analyzing 250 data points over nine months starting in May 2010.
“We did some sampling of shrimp and other types of seafood with trawler nets in Barataria Bay and found high levels of total petroleum hydrocarbons in marine organisms,” said Killian, who began working in the Gulf of Mexico as a commercial fisherman in 1981 and then became a research scientist studying the area in 1997. “I have never seen anything like what I’ve seen since the BP oil spill. This is not par for the course.”
Julie Anderson, an assistant professor at the LSU Agcenter and Louisiana Sea Grant, has done research on the effect of oil and dispersants on local crabs.
For one study, she exposed larval blue crabs to chemical dispersants used to clean up the oil spill. But she exposed the crabs to a much higher concentration of dispersants than what was used in the Gulf oil spill.
Anderson said she found it did not make much of a difference in the crabs’ death rate.
But when she exposed mud crabs to a combination of both oil and dispersant, the oil broke down more easily and was absorbed by the crabs. More of them died as a result.
“From my experiments, I would say it’s not the dispersant alone,” she said. “We did find that the dispersant made the oil more toxic because it brought it into the water instead of just keeping to the surface of the water.”
But, Anderson said, a disease found in local crabs last year may have been due to overpopulation the year before, when waters were closed to crabbers during the oil spill. That sickness may be contributing to the low harvest numbers crabbers have reported this year, she said.
Disproving the suggestion that the spill or its cleanup had an effect on seafood population is proving equally difficult.
Caz Taylor, a seafood researcher at Tulane, took samples of blue crab larvae in the Gulf in 2010 and again in 2011, hoping to determine if the spill had any effect on their population. The results, she said, were inconclusive.
“The idea was to see if there was any obvious drop in the numbers. It doesn’t seem like 2010 was a particularly bad year, but it’s hard to tell because we don’t have any baseline data. And it doesn’t seem like the number of adult crabs is related that the larval supply,” she said.
She also tested the crabs for certain chemicals that would suggest they’d been contaminated by oil from the Deepwater Horizon site.
“We hadn’t detected that oil has gotten into the crabs, but we don’t have any evidence that there isn’t oil in them, either,” she said. “It’s difficult to be positive about the absence of something.”
Staff Writer Cara Bayles can be reached at 857-2204 or at [email protected].
Fish & Seafood with Bill & Sheila
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