Lake Norman Number of dead stripers surges

[Striperjim]

Number of dead stripers surges

High temperature, low oxygen may be behind worst kill since '85
BRUCE HENDERSON

Staff Writer Charlotte observer


Nearly 300 striped bass have died on Lake Norman this week in the reservoir's worst kill of the species in nearly 20 years.

Biologists believe a combination of rising water temperatures and plummeting oxygen levels killed the fish. Stripers, an ocean-going fish stocked in Norman for anglers, sometimes can't survive such conditions in Southern reservoirs.
Between Monday and Thursday, Duke Power biologists counted 124 dead stripers floating between Cowans Ford Dam, on the lake's southern end, and Davidson Creek midway up the eastern side. On Friday, they found another 162.
Most were mature fish 20 to 22 inches long.
That's the largest striper kill on Norman since about 1985, said Duane Harrell, Duke's manager of scientific services. Duke normally finds five to 15 dead stripers a year.
Water readings this week remained within the limits of temperature (78 degrees) and dissolved oxygen (2 parts per million) that stripers require, Harrell said. Those factors are still suspects, however, because pollution would have killed other species.
"That's why this is obviously some environmental-type stressor that would be specific to stripers," said Christian Waters, a freshwater fish expert for the N.C. Wildlife Resources Commission.
Under natural conditions, striped bass would search out cool, deep waters in the ocean or sounds this time of year. But when they're captive in reservoirs, summers can be hard.
Water near the lake surface is warmer than stripers like, but it's rich in oxygen. Lower depths offer cooler water but less oxygen.
As summer wears on, the layer of cool water at the bottom doesn't mix with the surface, driving oxygen levels near zero. If those conditions develop quickly, trapped fish can die.
Over the July 4 weekend, about 1,000 stripers died on Badin Lake about 50 miles northeast of Charlotte, Waters said.
Parasites called gill maggots, common in stripers, might have added enough stress to send some fish over the edge. Dead fish have been sent to N.C. State University for necropsies.
"It's just one of those things that we may never know," Harrell said.
Striped bass don't reproduce in Norman. In nature, the fish swim up freshwater rivers to spawn. The reservoir doesn't offer the distance or the moving water their eggs need.
Even the hundreds of dead fish found so far aren't likely to hurt the lake's total population, Harrell said. But it's unknown whether the kill is just beginning or nearing its end.

[Striperjim]

August 6th 2010

HUNTERSVILLE, N.C. -- Since the middle of July, more than 6,000 striped bass have died in Lake Norman. Environmentalists are monitoring the water and focusing their search efforts around Duke Energy's power plant.
Each year, the lake is stocked with hundreds of thousands of striped bass.
Some die as part of a natural process – on average, 200 a year -- but it's much worse this year because the lake is severely oxygen deprived.
Wildlife experts say Duke Energy's McGuire Power Plant made the inevitable come much sooner. The company uses the water from Lake Norman as part of its cooling system and now crews are surveying the lake to monitor the damage.
“Part of that collection not only means collecting the fish but recording the length, the characteristics and any condition the fish are in,” said Duke Energy spokesperson Valerie Patterson.
While a significant number of fish have died, wildlife officials say most of the people who come out to fish probably won't even notice. They say the real problem will come if the same thing happens next year.
“If this type of event happens frequently, every year or every other year, that would put a lot of stress on the fishery. It would be difficult to recover,” Brian McRae, of the North Carolina Wildlife Resources Commission, said.
Officials from the Wildlife Resources Commission say this problem is not unusual and they expect everything to be back to normal soon. The commission plans to partner with Duke Energy and N.C. State University to further study why this is happening in lakes across the state.
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