Change in conditions or predators probably behind fish kill

By on March 18, 2015

dead fish

Dead menhaden near the  Duck research pier. . (NCDENR)

Hundreds of dead menhaden have washed up along the beach from Carova to Avalon Pier, causing wide speculation about the cause of the kill, including whether it was related to unexplained rumblings this week.

But fish kills are not uncommon and are usually from natural causes.

Jill Paxson, an environmental specialist with the North Carolina Division of Water Resources, said Wednesday that state experts are sorting through reports of the kill.

Generally, she said, such die-offs can be attributable to environmental factors such as an algae bloom causing oxygen levels to drop or sharp changes in water temperature.

It is doubtful that the fish are by-catch from trawlers, which discard species that they are not pursuing.

“Usually if it’s bycatch, it’s multiple species,” Paxson said.


Menhaden cover the shore break at Corolla. (N.C. Department of Environmental and Natural Resources)

The Virginian-Pilot quoted a state Division of Marine Fisheries biologist as saying that the fish were driven ashore by predators such as bluefish or striped bass.

A report by the National Marine Fisheries Service on a menhaden die-off on the North Carolina Coast in 1999 said that the schools of fish can become so dense that they use up their own oxygen and die. In that case, it was probable that predators exacerbated the situation.

A dolphin was reported to be among the dead fish in Corolla, but no information was available on whether the stranding was coincidental or related to the menhaden kill.

By fish-kill standards, this one was not particularly big. Paxson said one die-off covered the Neuse River for 30 miles.

Menhaden, which are caught by the millions for their oil and for use as animal feed, are extremely sensitive to environmental changes, Paxson said. Their skin is very thin, and scales fall off easily, exposing them to the elements and pathogens.




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