Why didn’t the boom translate into brimming crab pots? CBF Director of Fisheries
Bill Goldsborough explained that an unusually high proportion of the crabs—about
three quarters—counted in the 2011-2012
winter survey were juveniles, still too small
to catch by early summer.
Algal blooms fed by polluted runoff quickly die and decay, sucking up oxygen and
creating “dead zones.” The dead zones
force crabs to find oxygen in shallow waters
where they are more easily caught,
the Chesapeake Bay in the spring through
fall. Male crabs—called “Jimmies”—wrap
themselves around mature females—
“sooks”—to protect them from cannibals
and predatory fish for several days as the
females shed their shells.
Many of these crabs were
spawned in the late summer or
fall of 2011. Blue crabs normally
need about 12 months of growing time before their shells are
large enough to meet the 5-inch
legal catch limit, Goldsborough
said. The wave of juveniles was
spawned by a large number of female crabs
protected the previous year by Virginia and
Maryland’s catch restrictions. The number
of young crabs may have also been boosted
by tropical storms in the fall of 2011 that
swept more crab larvae into the Bay from
After being fertilized, female
crabs swim in the fall to the
southern Bay in an extraordinary spectacle called the “march
of the sooks” or the “sook run.”
They hibernate at the bottom of
the Bay. And then in the spring,
the females release millions of
larvae, which drift into the
Atlantic Ocean before being swept back
into the Bay by winds and currents.
Blue crab populations in the
Bay have nearly tripled over the last
five years because of restrictions
on catching females.
This year’s spike in young crabs may lead
to higher harvests next summer. But the
fact that the crab population often experiences booms and busts like this points to a
continuing problem, Goldsborough said.
Blue crabs can live for up to about four
years and can grow up to 10 inches across
the shelll from point to point. But until
Virginia and Maryland imposed restrictions
on catching crabs in 2008, two thirds or
more of all crabs in the Bay were caught
annually. This meant that most did not live
much beyond one or two years or grow
much larger than five inches.
“The crab population is truncated, meaning
we catch crabs so quickly, there are very few
crabs bigger than legal size,” Goldsborough
said. “As a result, the fishery is very
dependent on each year class that comes in.
And that creates instability, which is not a
good thing. We want more stability in the
crab population and more older crabs so
that we have ongoing high reproductive
potential. This would be good for both the
crabs and the crabbers.”
“Dead zones” also kill the food that crabs
eat, destroying or preventing the growth of
75,000 metric tons of clams and worms a
year in the estuary, according to a scientific study in the journal Science. That is
enough food to support half the commercial crab harvest.
One way to create stability in the crab population is for Maryland and Virginia to continue the science-based restrictions on
catching female crabs imposed in 2008.
Although some watermen have called for
relaxing the restrictions, lifting the protections now could lead to another collapse.
In an effort to shrink the Bay’s “dead
zones,” the U.S. Environmental Protection
Agency issued pollution targets for the
Chesapeake Bay in December 2010. These
targets have come under attack by industry
lobbying groups, however, and CBF is
fighting to defend them in court and in
Congress. (See Campaigns, page 10.) At the
center of this fight are blue crabs and the
more than 6,000 watermen and other
workers who depend on the crabs for their
“The blue crab was really affected most by
overexploitation by fishing,” said Dr.
Thomas Miller, Director of the Chesapeake
Biological Lab. “A decade ago, they were
experiencing 70 percent removal rates. And
you can’t take 70 percent of the trees and
still have a forest. And if you take 70 percent of the crabs, you no longer have a
healthy crab stock.”
Since 2008, fisheries managers in Maryland
and Virginia have been keeping total annual harvests below 46 percent of all crabs.
Regulators have also now adopted a target
of allowing no more than 25. 5 percent of
all females to be caught in any one year.
Another strategy to improve the long-term
stability and health of the Chesapeake’s crab
populations is to cut significantly the nitrogen and phosphorus pollution into the Bay.
Nitrogen and phosphorus stimulate explosive growth of algae, Goldsborough said.
Algal blooms darken the water, blocking
light and killing underwater grasses that
crabs need for shelter.
Callinectes sapidus—the latin name for
“beautiful savory swimmers”—are strange
and feisty mascots for the Chesapeake Bay.
Blue crabs swim sideways through the
water. They have five sets of legs, and are
propelled by tiny flippers called swimmerets. Blue crabs deploy their claws to
hunt everything from fish to clams, oysters,
worms, insects, and a large number of their
fellow crabs, including their own offspring.
If these limits continue, and the Bay states
are successful in reducing pollution, the
frequent crashes in the blue crab populations should moderate. And this should
allow the Chesapeake’s scrappy fighters to
continue their peculiar sideways march to
Blue crabs range along the Atlantic coast
from Nova Scotia to Argentina. They mate in
Tom Pelton, an award-winning
environmental journalist, is
Senior Writer and Investigative
Reporter for CBF. Read his blog
16 Summer 2012 ; cbf.org