More than 13 million fish died in "fish kill events" in North Carolina in 2009—the most in the 13 years that data has been collected. Eighty percent perished in one event last fall when too many fish and not enough oxygen killed 10.2 million Atlantic menhaden fish in the Neuse River, according to a presentation before the Environmental Review Commission last week. (Download the report, PDF 2.1 MB)
The fish kill event lasted 50 days from mid-September through October near the New Bern portion of the river and Broad Creek. Scrumptious algae attracted the fish, which range in size from 3 to 5 inches. Soon, an eight-mile long, 100-yard wide school of fish packed the river like sardines, but warm weather meant the water couldn't hold enough oxygen for them to breathe.
Tests showed no significant lesions on the fish, toxic algae or chemical compounds that could account for the die-off.
"The take-home message for why we saw so many dead and dying fish is low oxygen in the river at that given time at that given location," said Jason Green, a senior environmental specialist and division leader for the Neuse River Rapid Response Team. "These fish were in the wrong place at the wrong time."
There are economic consequences of such a large die-off. Menhadens are fished commercially and processed for their oil and bone meal, which is used in poultry and livestock feed, cosmetics and paint.
And environmentally, the fish kill is a harbinger of troubled waters, according to a Neuse Riverkeepers' report. Excessive algae is often a sign of high amounts of nutrients, such as phosphorus and nitrates, in the water. Nutrients are a byproduct of runoff from industrial livestock farms, stormwater runoff and fertilizer-rich discharges from home lawns.
As for the figure of 13.8 million, investigators used conservative estimates and say the actual total could be double that number.
Fish kill events, defined as 25 or more fish dying together, occurred in five of the state's 17 major river basins. There were 33 events total, a drop from 61 in 2008. But the events were far more deadly. There were 7.5 million fish deaths in 2008 compared with less than 1 million annually for four straight years.
Two thirds of the 2009 deaths happened in the Neuse (213) and Tar/Pamlico (113) estuaries, the report states. Estuaries, which mix fresh and saltwater, are particularly dangerous because they can't hold as much oxygen.
The Neuse, and mainly the Atlantic menhaden, accounted for 97 percent of all fish mortality in 2009.
"These are small, sensitive fish. They swim in large, dense schools," Green said. "They are clearly susceptible to low oxygen."
The last similar fish kill occurred in 2001, Green said, but that only claimed 200,000 fish. It's difficult to predict when the next one could occur, he said, because these events are often connected to the weather.
The Triangle region experienced only two fish kills. About 100 died in August at MacGregor Lake in Cary. Dead fish were discovered at the bottom of a spillway on the third consecutive day of 99-degree temperatures.
At Pine Lake near Roxboro, 100 fish died in May because of a lack of water in the pond combined with runoff from a leaking septic system upstream. (According to the fish kill report, "the system was recently dug up and repaired but is not permitted by the state and is still leaking based on fecal results obtained at the site.")
Sen. Floyd McKissisck Jr. (D-Durham), one of only a half-dozen committee members still in attendance when Green presented, asked how one disposes of 10.2 million dead fish.
Green said they disintegrate quickly, sometimes in only three days.
"And seagulls have a blast," said commission co-chairman Rep. Pryor Gibson (D-Anson).