November 14, 2018 — Warmer winters, rather than overharvesting, caused the steep decline of oysters and other commercially valuable shellfish in the Chesapeake Bay and elsewhere along the Atlantic coast, according to a controversial new study that’s getting pushback from some scientists.
The study, which appeared in Marine Fisheries Review, a quarterly journal of the National Oceanic and Atmospheric Administration, says that multi-year stretches of mild temperatures in normally weather months altered the food web in coastal waters. That impaired the growth and reproduction of oysters, quahogs, soft-shell clams and scallops, scientists said. It also led to increased predation on shellfish larvae and outbreaks of diseases.
“The temperatures got warm and that changed the whole environment, so [the oyster diseases] MSX and Dermo could flourish,” said Clyde MacKenzie, Jr., the study’s lead author and a longtime researcher at NOAA’s Northeast Fisheries Science Center at Sandy Hook, NJ. Mitchell Tarnowski, who runs the annual fall oyster survey for Maryland’s Department of Natural Resources, is the co-author.
The paper’s conclusions, especially its dismissal of overfishing as a factor in Chesapeake oyster declines, came under fire from scientists with the University of Maryland Center for Environmental Science and Chesapeake Bay Foundation. Its publication comes as the DNR prepares to release a first-ever stock assessment of the oyster population in the Upper Chesapeake, including an evaluation of whether current harvest levels are sustainable.
The scientific consensus has long been that overharvesting, disease and habitat loss over the decades devastated the Bay’s oyster population, with some estimates putting it in recent years at 1 percent or less of historic levels of abundance. From an annual commercial harvest of nearly 17 million bushels in 1880, landings have trended downward, hitting historic lows in 2003-04 of just 50,000 bushels. The harvest has rebounded some since then, though much of the gain has come via private oyster farming, especially in Virginia.
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