Another Bay Scallop Die-Off In Bays Looms, But Giant New Generation Leaves Room For Hope

Sawyer Clark shows off some of the baby scallop "bugs" that are abundant in the Peconic Estuary this summer. But their adult progenitors appear to have died in huge numbers over the summer, for the third summer in a row, leaving few hopes for the fall harvest.

The good news, marine biologist Dr. Stephen Tettlebach said this week, is that the bay scallops in Peconic Bay and its tributaries had perhaps the most successful spawning year this year that he has ever seen, in 30 years of monitoring the delicate and valuable shellfish species.

The bad news, unfortunately, is that for the third year in a row the adult scallops appear to have died, or are dying, en masse, after having spawned earlier in the summer and that there is once again little hope for a November harvest bounty.

Researchers from the Cornell Cooperative Extension Marine Program in Southold have been conducting monthly underwater examinations of the scallop stocks in seven locations around the Peconic Estuary — from Flanders Bay to Napeague Harbor — to track the health of the stock in the wake of the massive die-offs in 2019 and 2020.

The results from their dives on designated areas last week showed that high numbers of the scallops — perhaps as much as 90 percent — had died in the weeks since they last surveyed.

“Up until a few weeks ago, we thought the adult populations were doing all right, but last week the numbers of adults had declined really sharply in almost all the areas we looked at,” Dr. Tettlebach, who led Long Island University’s efforts to rebuild the bay scallop stocks after the devastating “brown tide” algae blooms of the 1980s and 1990s, said. “So it’s not looking good for the harvest again.”

The devastation on the bay bottoms stands in stark contrast to what the scientists and those who are on the water are seeing in other parts of the bay, where the new generation of scallops are swarming in astounding numbers.

“When we were pulling out … our trap Friday before the storm, they were running off of it like gravel,” Jon Semlear, a Noyac bayman said. “The most I’ve ever seen on a net. They’re the size of a dime or a nickel. Normally, we would be worried, did they spawn, instead we’re seeing this but are they just all going to die again?”

“Monster numbers,” Dr. Tettlebach said of the young-of-the-year. “I think the biggest scallop set I’ve ever seen.”

Scallops generally have a life span of only about 12 to 18 months. So they would typically only live through one full spawning cycle — though many are believed to spawn twice in a given season, in the summer and again in early fall, if they survive that long. The annual November-March harvest season has long been scheduled as such to take advantage of that lifespan, reaping the bounty of the stock without interrupting the spawning that replaces it for the following year.

That the scallops have managed to persevere at all through successive years of such massive mortality is a miracle of their life cycle — but also a tenuous pattern that would seem to have the iconic shellfish teetering on the brink of annihilation if there were to be a year when the adults did not spawn successfully, as has been common in the long term.

The causes of the die-off this year follows the story from the last two years nearly to the letter: the adult scallops that emerged from the previous year’s spawn appear healthy and abundant in the spring and early summer; the scallops spawn in June and early July as they always have and millions of their tiny offspring start to grow on fronds of sea grasses, dock pilings, fishing nets and anything else they can attach to; then suddenly in late July or early August, the adults die in massive numbers.

A wholesale disease has been ruled out because the young-of-the-year “bugs,” as baby shellfish are known, survive and seem to thrive. Predators do not seem to be the main issue, since most of the dead scallops’ shells remain behind, untouched.

Scientists have identified a previously unknown parasite in the adult scallops but have said the infestation could not alone be responsible.

Instead, water temperatures in the Peconic Estuary, which have trended steadily upward over the last two decades and in the last three summers have reached levels that scientists know can be fatal to bay scallops, appear to be the foundational problem.

The generally accepted understanding of what is happening is that the environmental stress of the high water temperatures and the parasite, combined with the natural weakening of the scallops that comes with the exertion of the annual spawn is simply pushing the scallops past their tolerance level.

Dr. Tettlebach said that water temperatures in the bays are similar to what have been seen the last two summers at this point, in the high 70s in the eastern portions of the bay and low 80s in western corners, like Flanders Bay.

“That’s toasty for scallops,” he said.

The lone bright spot for adult scallops, the surveys have revealed, is in Napeague Harbor, where the mortality of adults has been much lower and a substantial number of adult scallops remained alive as of last week. But this week’s high temperatures could still pose a threat to the stocks there as well.

Also concerning has been the arrival of cownose rays, a species of voracious stingrays that swarm in schools of dozens or hundreds and consume shellfish, especially scallops. The species had previously been rare in local waters, but has swarmed in huge numbers the last three summers.

The surveyors say they will return to their test sites in mid-September to tally the extent of the devastation, though hope for improvements is, or course, nil.

“Its a very frustrating situation,” Dr. Tettelbach said on Monday. “The adults are getting the chance to spawn once and we’re seeing these very high levels of recruitment, which happens periodically in any species. But then the adults are all lost.”