By the turn of the century, though, winters will decrease from an average of 117 days to about 90, based on the study’s conservative estimate of temperature changes. A liberal estimate cut the season by half, to fewer than 60 days. The study’s analysis relied on 100 years of reported temperatures from gauges close to the University of Maryland Center for Environmental Studies near Cambridge.
As a result, Maryland’s waters are expected to become as warm as those in Newport News and possibly Morehead City, N.C., where blue crabs don’t need to burrow during winter. About 75 percent of juvenile crabs survive the bay’s winter waters. If the study’s findings are accurate, that number will approach 100 percent, said Hillary L. Glandon, a researcher at the University of North Carolina at Wilmington, one of the three authors.
The study published Thursday in the journal PLOS One has major implications for management of the bay’s wavering blue crab population, which supports a fishery worth hundreds of millions of dollars each year. Fishery managers in Maryland and Virginia have each placed limits on commercial crabbing to protect the animal in the hopes of boosting their struggling population.
In this year’s annual baywide winter survey, the overall population nearly hit 600 million, a positive step for the crustacean, whose numbers fell to a critical low of 251 million about 12 years ago. But historical numbers were significantly higher before water quality, disease and relentless fishing imperiled the stock.
A quarter-century has passed since the survey estimate last reached 800 million. In one brief shining moment early this decade, the juvenile population alone nearly matched this year’s overall population. It fell below a paltry 200 million last year before bouncing back to about 300 million this year.
Blue crabs will be “a climate change winner,” said study co-author Tom Miller, a professor at the U-Md. center, “because they are a more tropical species.” Blue crabs range along the coastal Atlantic from Argentina, across the Caribbean Sea, all the way to New England up to Cape Cod.
According to Miller, it was one of the rare positive effects from climate change. “We always hear about those species that are going to struggle or move. Blue crabs are going to do better.”
Except there’s a “but,” and it’s a big one, said Anson Hines, director of the Smithsonian Environmental Research Center in Edgewater, Md., along the bay.
Hines said the study does a good job tracking the changing climate and showing the unsurprising finding that a tropical species would flourish in warmer waters. But he emphasized another finding of the research, which shows that “things are not so simple.”
A warming climate could lure more southern predators that enjoy snacking on blue crabs to the Chesapeake. On top of that, “warmer temperatures may have negative impacts on resources that are good for crabs,” Hines said. That includes underwater grasses in which they hide from predators, along with their own major food source, Baltic clams, that might not survive the warmth.
“An added interesting aspect of this paper is that warming may also prolong the fishing season, which could add more difficulty in managing a fishery that has a history of … intense pressure,” Hines said. And humans are the crabs’ top predator.
It’s not the first time researchers peered into the future and saw good news for crabs. In a 2013 study, a marine geologist at the University of North Carolina’s Aquarium Research Center said crabs will bulk up on carbon pollution and supersize their growth in the next 75 to 100 years. That was great news for crabs and bad news for the oysters they bang open with their huge claws to eat.
Glandon said researchers embarked on the new study to provide useful information to fishery managers about the future of the crab business. “We know what will probably happen in five years, but not much beyond that,” she said.
Managers can expect to start seeing a significant shortening of winters and a blue crab population spike in 20 years, Glandon said. She was reluctant to make predictions because weather analysis isn’t always precise. “This is the tricky thing about modeling; it’s only as good as the data you put in it.”
Glandon was thankful to have data from bay gauges dating back more than 90 years. “Can you believe, in 1938, someone said let’s measure water temperature every day?” she said.
The most eye-opening findings were that winter would grow shorter and more crabs would live. “There will be a wintertime, but not long enough to cause mortality in crabs. I found that surprising,” Glandon said.