Causes of Fish Skin Lesions Ruled Out, Except for BP Oil Spill, New Study Says

Percentage of fish within a species or species group with skin lesions examined at 26 stations in 2011 (red) and 2012 (gray) in theGulf of Mexico. Abbreviations: O/R is the odds ratio of the differences between 2011 and 2012, and n.s. means not significant. (Transactions of the American Fisheries Society)

(Click to enlarge) Percentage of fish within a species or species group with skin lesions examined at 26 stations in 2011 (red) and 2012 (gray) in theGulf of Mexico. Abbreviations: O/R is the odds ratio of the differences between 2011 and 2012, and n.s. means not significant. (Transactions of the American Fisheries Society)

A team of scientists studying the cause of skin lesions found on fish in the Gulf of Mexico in 2011 and 2012 have been unable to rule out toxic chemicals contained in oil released during the BP Deepwater Horizon oil spill as their cause, according to a peer reviewed study released Monday (Aug. 4).

(From Mark Schleifstein, | The Times-Picayune ) —  “We can’t say with 100 percent certainty that it was the Deepwater Horizon oil spill, but we can say what it wasn’t,” said University of South Florida marine science professor Steven Murawski, principal investigator with the university’s Center for Integrated Modeling and Analysis of Gulf Ecosystems, and who served as the senior science adviser at the National Oceanic and Atmospheric Administration during and immediately after the spill.

And what it wasn’t was basically everything else, Murawski said.

“We’ve analyzed the other potential sources and the one that correlates the best is the Deepwater Horizon,” he said.

The study was published in the Aug. 4 edition of Transactions of the American Fisheries Society, and was authored by Murawski and another USF scientist and two scientists from state research institutes. A copy of the study is available at Murawski’s web page.

The paper was co-authored by William Hogarth, who serves as director of the Florida Institute of Oceanography and was formerly the assistant administrator of the National Marine Fisheries Service.

The scientists’ findings were immediately disputed by Geoff Morrell, a senior vice president with BP, who said such lesions “have long been observed in the Gulf and have little effect on a species’ health or population.”

Morrell said such lesions in the past have been linked to agricultural and industrial activities along the gulf and the Mississippi River, and a variety of other factors.

He said the scientists also ignored earlier studies on the prevalence of fish lesions in the Gulf that were conducted before the spill, and also ignored information about the age, range and habitat of the fish that might have pointed to more likely causes of the lesions.

In addition, the study ignores and runs counter to data from thousands of water samples that show that the PAH exposure levels were too low to have significantly increased the incidence of fish lesions,” said Geoff Morrell, a senior vice president with BP. “Despite these and other shortfalls, the researchers themselves still admit ‘we cannot definitively link cause and effect using only 2 years of post-event data.’ “

According to the paper, however, the study eliminated many of the causes cited by BP, including stress from low salinity water or high temperatures. Also eliminated were illnesses caused by bacteria or diseases, Murawski said.

“We did pathology work, and this was not like an outbreak of an ebola equivalent for fish,” he said.

What is known is that similar outbreaks of lesions have been linked to toxic chemicals, especially polycyclic aromatic hydrocarbons like those found in the oil released for 87 days from BP’s Macondo well.

The greatest number of lesions were found in 2011 in bottom-dwelling species along the continental shelf just north of the BP Macondo well, according to the paper.

The good news is that the lesions were being found less frequently in 2012, the second year of the study, than in 2011, and continued to be seen less frequently in 2013, beyond the time frame of this study, Murawski said.

The scientists evaluated the disease status of 7,433 fin fish, representing 103 species caught at 150 sampling stations, in 2011 and 2012, examining them for skin lesions. The rates of lesions varied widely with species, area and depth.

The researchers found relatively high concentrations of PAH metabolites -– the chemical compounds left behind when PAHs are broken down inside a fish’s body -– in fish bile in 2011, the paper said.

But significant declines in the amount of two metabolites –- naphthalene and phenanthrene -– were found in red snapper between 2011 and 2012, which the paper said seemed to indicate that the exposure of the fish was episodic, rather than continuous or chronic.

While that’s good news for the fish, Murawski said it also lends more credence to the exposure being caused by the BP spill, rather than by spills from other wells or oil from seeps throughout the Gulf. The study said the chemical makeup of the PAH compounds found in the fish was very similar to that of the BP Macondo oil.

“The Gulf is full of oil wells and seeps, and if these were due to continuous exposure (from those other sources), we wouldn’t see a 50 percent statistically significant drop in these fish,” he said. Adding to the evidence that it was caused by the spill is that the amount of oil released in the spill in the relatively small area of the northern Gulf of Mexico was eight times greater than the amount of oil released by other wells and seeps in the entire Gulf.

Additional research still underway by Murawski and his team includes a study of a related long-term issue: whether the spill may be linked to a recent drop-off in the number of juvenile red snapper in the northern Gulf of Mexico.

“We don’t know if this is the result of some cyclical pattern or it’s caused by the Deepwater Horizon, but the stock of red snapper was going up at a significant rate until the spill,” he said.

Fishing for red snapper has been managed carefully for years because of concerns about overfishing, largely the result of the capture of juvenile fish in shrimp nets as “bycatch.” But federal and state officials have required shrimpers to install “bycatch reduction devices” on their nets to reduce the loss of younger fish.

“It’s going to take a couple more years of monitoring to see whether there’s a real trend,” he said, pointing to the collapse of at least one fish species in Alaskan waters in the aftermath of the 1989 spill of oil from the Exxon Valdez tanker in Prudhoe Bay.

“Whether or not the exposure to oil in such high concentrations had a genetic impact on them is unclear,” he said. “It’s not only the contamination of the animals that are there, but modification of their genomes that’s the concern. It’s more problematic than the loss of a single generation.”

Murawski said one of the problems he and other researchers investigating the effects of the BP spill are facing is the lack of basic information about fisheries and the environment of the Gulf before the spill.

“One of the problems that all of us as analysts have is the very small number of baseline samples prior to the spill,” he said. “If the oil industry is going to engage in this kind of large-scale, diffuse extractive activity, then we should have much more in terms of baseline samples of sediment and fish, so you know what the Gulf was like the day before the accident and the day after.

“That would make our interpretation of the cause and effect to be much more straightforward,” he said.

Murawski said the cost of such sampling should be considered a cost of doing business in the offshore drilling industry.

The study was paid for by grants from the National Marine Fisheries Service and NOAA, The Louisiana Oil Spill Coordinator’s Office, and by the BP-Gulf of Mexico Research Initiative, an independent research program financed by a $500 million grant from BP.

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