Saving Seafood

New study: Chesapeake oyster decline not due to overfishing

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.

Read the full story at the Bay Journal

 

Study says ocean oscillation changes reduced shellfish landings

November 6, 2018 — For years, Maine shellfish harvesters have been complaining that there are fewer softshell clams while arguing that the diggers who go out on the mud flats aren’t the cause of the problem.

A recent study by researchers from NOAA’s Northeast Fisheries Science Center and the Maryland Department of Natural Resources backs them up on both counts.

According to Clyde L. MacKenzie Jr. of NOAA and Mitchell Tarnowski from the Maryland Department of Natural Resources, between 1980 and 2010, documented landings of the four most commercially important inshore bivalve mollusks along the Northeast coast — eastern oysters, northern quahogs, softshell clams and northern bay scallops — dropped by 85 percent.

The principal cause, they say, was warming ocean temperatures associated with a shift in the North Atlantic Oscillation which resulted in damaged shellfish habitat and increased predation from Maine to North Carolina.

“My first response is that the article confirms what I have been seeing with soft-shell clams over at least the last decade or so,” Brian Beal, a professor of marine ecology at the University of Maine Machias and director of research at the Downeast Institute on Great Wass Island, said last week.

The North Atlantic Oscillation is a fluctuation of atmospheric pressure over the North Atlantic that affects both the weather and the climate along the East Coast, especially in winter and early spring.

According to NOAA, shifts in the oscillation can affect the timing of a species’ reproduction and growth, the availability of microscopic organisms for food and predator-prey relationships.

Over a period of several years, MacKenzie and Tarnowski interviewed shellfish wardens and harvesters along the New England coast, as well as examining landings records and other research in an effort to determine the “true causes” of the precipitous drop in shellfish landings.

Read the full story at The Ellsworth American