Friday, February 20, 2015

Female Blue Crabs Go the Extra Mile

The Washington Post recently ran an article on the status of blue crabs in Chesapeake Bay. The first few paragraphs and a link to the full article are posted below. The Post site has a nice graphic of the blue crab life cycle.



 February 12  
Deep under the cold, dark waters of the Chesapeake Bay, the answer to whether the decimated blue crab population can survive lies buried in mud.
Tens of millions of female crabs are scattered across the floor of the lower bay in southern Virginia, where the estuary pours into the Atlantic Ocean, waiting out winter for one of the most important events in their short lives. When spring comes, they will inch closer to the ocean with billions of eggs.
It’s a critical time because the blue crab population is reeling, facing some of the lowest numbers in history. Officials are desperately hoping that steps taken to protect females last year will allow the fishery to rebound from the edge of disaster. But those efforts are also mired in a debate over the best way to protect the crabs.
As females go, so go blue crabs. Last year, scientists estimated that there were only 68.5 million females old enough to spawn, far below the 215 million that officials say are needed to overcome natural threats such as predators and cold — and human threats such as commercial overfishing — without depleting the population. This year’s count is underway by Maryland and Virginia scientists at 1,500 locations.
The blue crab, Maryland’s state crustacean and a symbol of pride for the region as much as a resource, is more threatened now than at any time since biologists started to record numbers in the late 1940s. Both watermen and state officials are deeply worried about blue crabs’ future. Sixty years ago, the Chesapeake Bay yielded 75 percent of the crabs harvested in the United States; now the withered stock yields about 35 percent, according to a report by the Maryland’s natural resources department.
Some watermen say the steps taken by Virginia, Maryland and the Potomac River Fisheries Commission to rescue crabs after the population’s free fall in 2008 haven’t worked. The states cut the number of females that can be fished by about 30 percent. When the stock rose only to fall hard again last year, Virginia cut the number of females that could be fished by an additional 10 percent during the spawning run.
Smithsonian scientists worry that efforts to save females might produce a serious side effect: overfishing males. When male crabs decline, those remaining mate more often, and sometimes can’t regenerate their sperm supply quickly enough, according to a study by the Smithsonian Environmental Research Center.
Read the rest of the article at the Washington Post by clicking here.

Monday, February 2, 2015

American Indians, Colonists had an Appetite for Crabs

Flickr photo by Rhea C

SmithsonianScience.org has an article about my lab's recent paper on blue crab remains found in Chesapeake Bay archaeological sites.

By John Barrat

Native Americans and America’s early colonists ate many more blue crabs than modern researchers previously thought, according to a team of scientists studying crab remains unearthed at archaeological sites in the Chesapeake Bay area.
Because so very few crab shells have been recovered in archaeological digs in the midAtlantic, anthropologists and others have long assumed that crabs were eaten rarely, if at all, by Native Americans or colonists there.
Now a comprehensive review of 93 archaeological sites across the Chesapeake Bay dating back to 1,200 B.C. has turned up evidence showing quite the opposite.
“I don’t feel confident saying crabs were consistently a dietary staple for Native Americans, but they are found in so many different sites across so many different time periods that we know Native Americans and the colonists were clearly eating them,” says Torben Rick, an anthropologist at the Smithsonian’s National Museum of Natural History. Rick was lead author of a recent paper on the subject in Journal of Archaeological Science.
The researchers found little mention in archaeological studies of the remains of blue crabs in the Chesapeake region, says Matt Ogburn, a crab ecologist at the Smithsonian Environmental Research Center and co-author of the paper. 

“Initially, when we began reviewing Chesapeake sites, we thought we might find 100 or, if lucky, 200 pieces of crab remains and claws to work with. But it turned out there is a lot more out there than we expected,” Ogburn says.

As the paper reveals, by looking into museums and other repositories “we identified and evaluated more than 900 crab remains collected from archaeological sites,” Ogburn adds. The findings ran counter to “the widely held hypothesis that people in the past did not eat crabs,” the scientists say.
“Blue crabs were an important food source for Native Americans, Euro American colonists, and African Americans,” Rick, Ogburn and their co-authors write in their paper. “They are found at a wide variety of site types, including George Washington’s Mount Vernon Estate, a series of plantations and manors in Maryland, a 17th century Native American site, and a 19th-20th century African American domestic site (Sukeek’s Cabin). These crab remains range in age from the early 17th century to the 20th century, suggesting continuous consumption of crabs from prehistoric times and across all major cultural or ethnic groups (Native American, Euro American, African American).”
Why hasn’t previous research found evidence of crabs? The answer is in the shells.  “The blue crab carapace is so fragile and friable that it just doesn’t preserve that well over time,” Rick says.  The shell pieces have often gone unrecognized during archaeological digs.
In this new study, Rick and the other scientists conducted experiments with crab remains showing just how susceptible blue crab shells are to being scattered by scavengers, dissolved and etched by acidic soil, and fragmented into tiny pieces during decomposition and burial. Because the  shells break into such tiny pieces, archaeologists needed special tiny gauge screens to recover the  fragments.
By measuring the excavated the crab parts–primarily pieces of claws and shell parts–the researchers determined that large crabs were more common in the archaeological collections compared to crabs caught in the Chesapeake today.
“Large crabs overall seem to have been quite a bit more common in prehistoric times than they are today,” Rick says. “That’s what we would expect, but it is good to have scientific confirmation that today’s smaller crabs are in part the result of an intensive fishery that removes large crabs from the population.”