Scientists Say More Than One Factor Likely Responsible For Bay Scallop Die-Off This Year

Dr. Christopher Gobler. DANA SHAW

A month after early hopes for a robust scallop harvest on the East End were dashed when baymen found next to no living specimens in their dredges on opening day, scientists gathered at the Stony Brook Southampton college campus on Friday night, December 6, to deliver a post-mortem.

Rather than offering a single cause, such as the brown tide that has in the past been responsible for similar widespread die-offs but was absent this year, the participants in a symposium presented by Stony Brook University’s School of Marine and Atmospheric Sciences offered a number of explanations — including higher water temperatures brought on by climate change, which put the bivalves under increased stress to opportunistic diseases, and predation from cownose rays, a species that has been newly found in New York waters in recent years.

Dr. Christopher Gobler, the host of the event, did offer a sliver of hope for baymen who saw a major portion of their income vanish along with bay scallops this season. He announced that Governor Andrew Cuomo had asked the federal government to issue a disaster declaration for the Peconic Bay scallop fishery and to provide federal aid to baymen, and funds to help remedy the problem.

Although the scientists could not pinpoint a single reason for the scallop population crash, Dr. Gobler did dismiss two reasons that he said have been erroneously bandied about. One suggests that there wasn’t enough nitrogen in the bays to support the growth of enough of the microscopic plant matter scallops feed on, while the other lays the blame on competition for food from the growing number of oyster farms in East End waters.

But scientists have long pointed to high levels of nitrogen oozing from septic systems or coming in the form of fertilizer runoff as a major cause of the brown tide and other algal blooms that choke off shellfish, and Dr. Gobler said studies showed the level of nutrients in the bays remained fairly constant from 2014 to 2019.

Dr. Gobler said that if each of the 4 million oysters harvested in 2018 filtered 200 liters of water a day, it would take them nearly three years to filter all the nutrients from the bay, making it impossible for them to have had an impact on scallops.

“We live in an era when people are privy to their own facts, and alternative facts,” he said of the debunked theories.

If competition for a limited supply of food isn’t to blame, what is?

Dr. Stephen Tettelbach of Cornell Cooperative Extension, whom Dr. Gobler described as the top expert on Peconic Bay scallops, acknowledged that the abrupt die-off, eliminating what last year was thought to be a promising set of scallops for this season, remains something of a mystery.

“Historically, the scallop fishery is notorious for booms and busts,” he said, noting that the most recent busts were those associated with five outbreaks of the brown tide, beginning in 1987, when annual landings were reduced from an average of 300,000 pounds to virtually nothing.

After years of little to no scallops to be had, their numbers were restored by large-scale plantings of hatchery-raised populations, Dr. Tettelbach said, resulting in several years of reasonably large harvests.

Although early surveys this summer showed a large number of healthy scallops this year, Dr. Tettelbach said later surveys showed few, if any, adult survivors.

“Everything was looking great, up until the end of 2018,” he said. “The harvest was really good. There was a great set of scallops in 2018, so expectations were really high for a good harvest season this year.”

He said 2019 was a warm year, with water temperatures reaching bathtub levels of 85 degrees this summer. Scallops can survive in water up to 88 degrees — but warmth causes stress.

“One of the things that is a possible explanation for some of the die-off is there is a certain level of physiological stress to scallops at the time of spawning, or after spawning, and in conjunction with high water temperatures, and/or low dissolved oxygen levels,” he said.

Dr. Gobler also touched on environmental causes, noting that oxygen levels go down as water temperatures go up, putting stress on shellfish and other sea life.

He added that carbon dioxide from the atmosphere is absorbed by the ocean, making the water more acidic, which also causes stress to shellfish. The less oxygen, the higher the acid levels, he added. “The bottom line is, this population is very sensitive to acidification,” he said.

Dr. Gobler also pointed out that scallops’ heart rates tend to rise with rising water temperatures, putting even more stress on the animals.

Debbie Barnes, director of shellfisheries for the New York State Department of Environmental Conservation. DANA SHAW

Dr. Bradley Peterson said loss of habitat, often blamed when scallops die off, was not the cause this year. Nor was there an abundance of whelk, a larger shellfish that feeds on adult scallops, to account for the mortality rate.

But if the animals died because of stress, one would have found their shells — and that was not the case, he said.

Dr. Peterson said cownose rays, which can grow to be 40 pounds, have been seen in New York waters as temperatures rise, and said he had been told of one school of the fish that stretched for a quarter mile and was at least 800 feet wide in Center Moriches last summer.
The rays have been responsible for similar scallop die-offs in the Chesapeake Bay.

Furthermore, they crush scallop shells when they eat them, leaving little evidence behind, he said.

Fishermen who set pound traps east of Jessups Neck reported finding rays in their nets this summer, he said, leading him to believe they played some role in the loss of this year’s crop of scallops.

Although there was no outbreak of any single disease this summer, Dr. Bassem Allam, a Stony Brook scientist who studies disease in shellfish, said many of the diseases that do affect shellfish can be more lethal when they are under increased stress from environmental conditions such as high temperatures.

Dr. Joyce Novak, the director of the Peconic Estuary Program, said her group’s technical committee had already met to discuss the fate of the scallops and would continue to do so over the coming months, and Debbie Barnes, the director of shellfisheries for the State Department of Environmental Conservation, said the DEC stood ready to lend its expertise to finding a solution.

“It could take several months — it could take a year,” she said of the governor’s request for federal disaster aid. “The process has been initiated, and that’s the first step.”