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Gulf oil spill jitters: a false fish kill alarm

August 24, 2010 |  6:59 pm

Louisiana officials backed off alarms they had sounded Monday about a Gulf of Mexico fish kill, saying that the kill was far smaller than they had reported and was the result of low oxygen levels unrelated to the BP oil spill.

A news release issued Monday by St. Bernard Parish had quoted Parish President Craig Taffaro saying, "By our estimates, there were thousands, and I'm talking about 5,000 to 15,000 dead fish." It also noted that a half-mile-long swirl of thick substance with several tar balls and a strong smell of diesel was discovered around Louisiana's Grassy Island.

However, Taffaro was also quoted as acknowledging that "we don't want to jump to any conclusions because we've had some oxygen issues by the Bayou La Loutre Dam from time to time."

In a follow-up news release Tuesday, the Parish announced: "Biologists from the Louisiana Department of Wildlife and Fisheries conducted a thorough investigation of a fish kill found in the Mississippi River Gulf Outlet (MRGO) over the weekend. They found low oxygen levels to blame and have confirmed the kill is a result of natural events and is not associated with the Deepwater Horizon oil spill. 

"High nutrient content from the Mississippi River in combination with seasonal occurrences have been the cause of hypoxic conditions for years. Although essential in fertilizing the estuaries, in some cases the nutrient load is too great and hypoxic conditions arise. 

"Hypoxic events typically occur in late summer to fall and are also associated with processes that bring deep low-oxygen water to the surface. Fish need an oxygen level of at least three parts per million to survive.

Measurements taken by LDWF staff at various samples sites showed less than one part per million of oxygen at the bottom of the water. A "borderline" oxygen level of perhaps three parts per million was found at the top.

"The only large concentration of dead fish was noted in a bayou immediately adjacent to the MRGO. An estimated 500 fish were found in the area. The dead fish found appeared to be roughly five days old. Species observed included large red drum, sheepshead, hardhead catfish, spotted sea trout, croakers and stingray.

"Seasonal fish kills are normally found in much of southern Louisiana associated with low oxygen events.  LDWF biologists expect these to be common in areas such as marinas, dead-end canals, and other areas with poor circulation."

Ralph Portier, a Louisiana State University biologist, had expressed skepticism Monday that the kill could be spill-related, but added in an interview, "It goes to show how sensitive the [oil spill] issue is. You can imagine the angst of a lot of people in the seafood industry when they hear about a fish kill now."

-- Margot Roosevelt