Scientists know more about the blue crab than just about any other species in the Chesapeake Bay. So when millions of young crabs vanished in 2012, scientists became detectives, searching for clues.
Every winter since 1990, scientists dredge hibernating crabs from the muds of the Chesapeake Bay to check in on the population. In 2011, they estimated an astounding 800 million crabs, the most in nearly 20 years. Some 600 million were juvenile crabs that would be ready for harvest by the summer of 2012. Then they disappeared.
“We had two general ideas as to what might have happened to them. The first one is that they weren't really there, that somehow the survey was wrong. The second idea is that they were really there but something caused them to die at unexpectedly high rates.”
Tom Miller is a professor at University of Maryland Center for Environmental Science Chesapeake Biological Lab. He built a chronology using data from all around the bay. The main suspect, the winter dredge survey, was cleared, leaving Miller with no smoking gun and no bodies. But he was able to piece together where they might have disappeared.
“In the southern regions it was a perfectly normal year but there was something odd from the middle of the bay north going on that was causing an unusually high mortality or unusually low survival of crabs between the winter of 2012 and late summer.”
Across the bay, Rom Lipcius, Miller's opposite number at the Virginia Institute of Marine Science is looking at what he considers the number one suspect - red drum, a finfish that loves crab as much as people do. In 2012 as the juvenile blue crab population hit historical highs, so did red drum.
“So they can be voracious predators and in some cases large red drum can have upwards of 100 or more juvenile crabs in a single fish.”
On the York River three young VIMS scientists collect samples of juvenile crabs by vacuuming them up. They're small enough to fit in a tablespoon. Mandy Bromilow, one of Lipcius' students, tethers them to a pipe, much like that poor goat in Jurassic Park. She uses a Go-Pro to record what eats them, which is mainly other crabs.
“I'm doing some gut content studies where I go out and collect fish and I found juvenile blue crabs in the stomachs of striped bass and Atlantic croaker as well.”
About an hour from VIMS, Mike Croxton and his wife Tammy are unloading bushel baskets of crabs from pickups that back up to their dock. The 2012 mystery is history. So far this year, crabs have been plentiful. There's stories and teasing. Like blue crabs, watermen are becoming rare.
“I'll tell you what, last time I was down at Mariner's Museum I saw Edward Painter on the wall and a lot of them old fellers I ain't seen in years.”
Croxton's 79-year old father, “Big Mike” has worked the water since he was 12. Like most watermen, he knows nature and its cycles and can usually predict where the crabs will be, but...
'Every time you think you've got them figured out, in my experience, they make a fool out of you every time.”
And Tom Miller:
“And just when you think you understand, nature can throw a curve and remind you you're not quite as smart as you think you are.”
Lipcius makes projections not predictions about blue crabs. His goal is to better understand what's happening out in the bay.
“The mystery continues. We can identify the most likely causes but we'll never really know for sure. It's not unlike will we ever really know whether or not O.J. did it.”
Scientists findings about the missing blue crabs of 2012 are due out at the end of this year.