A fungus called Aphanomyces invadans paired with abruptly cooler temperatures over the past two weeks are the likely sources behind fish kills erupting in the region’s rivers.
According to Heather Jacobs Deck, Pamlico-Tar River Foundation river keeper, reports of fish kills have come in from the Pungo River region and its creeks, as well as the South Creek area, Camp Leach, Crystal Beach, Broad Creek and Blounts Bay. The only fish that have been affected are juvenile menhaden less than 5 inches in length.
While such events are somewhat atypical this time of year — usually major fish kills come with summer’s heat and low oxygen counts — Deck said what is unusual are the numbers and the geographic extent of the fish kills. Dead baitfish, as menhaden is known, have turned up in large numbers in the Neuse, Pamlico and Pungo rivers almost simultaneously.
Thursday, Deck collected water and fish samples from Blounts Bay to send to the laboratory of the North Carolina Department of Environmental and Natural Resources for study. By her estimate, 175,000 fish had been killed in Blounts Bay alone.
“We could be looking in the several hundred thousand into the millions range,” Deck said.
A. invadans outbreaks affect many species of fish inhabiting fresh and brackish waters worldwide. According to a study done by the U.S. Geological Survey, low salinities appear to be crucial to the fungus, so its spread in brackish water is
associated with rainfall. Fish infected with the fungus, also called slime mold, develop ulcerous lesions which lead to necrosis of surrounding tissues and, ultimately, death.
“A lot of times you’ll see a mix of species, but this is just (affecting) menhaden,” Deck explained. “About half of them have lesions. That’s just the slime mold. It looks like something took a bite out of them.”
Whether the fungus is the only culprit responsible for the fish kills is harder to determine, said Deck. Fish in the region deal with many stressors in the summer — low oxygen, nutrient pollution which can cause harmful algal blooms, high temperatures — all of which can make fish more susceptible to diseases this time of year, she explained. The samples pending will be able to better pinpoint the exact causes.
Whether the fact that a large number of juvenile baitfish are being removed from the food chain has any impact on the rivers’ larger species of fish is unclear at this time.
If what has happened on the Neuse River over the past month is any indication, Deck said the fish kills on the Pamlico and Pungo rivers could continue for several weeks. In the meantime, she advises that people, and their pets, avoid contact with waters where there is a visible fish kill.