in this episode we ask the question how do scientists track and monitor blue
crab populations in the Chesapeake Bay?
hey Josh Bernstein here i'm in annapolis maryland enjoying a local favorite the
blue crab
what the lobster is to Maine the blue crab is to maryland
they love their crabs here and rightly so
millions of crabs are harvested each season from the Chesapeake Bay watershed
and they bring in a lot of money but there's a problem in recent years
blue crab populations in the Chesapeake have plummeted
I want to know why to learn more about the situation i'm driving to edgewater
maryland to visit SERC the Smithsonian Environmental Research Center
I've arranged to meet dr. tuck hines marine ecologist and search director
tuck and his team study the factors that affect blue crab populations and he's
offered to show me how they track and monitor the blue crabs
Smithsonian Environmental Research Center has been studying the rhode river
system as a part of the larger chesapeake bay for 50 years now
every month we're out trawling to catch crabs which is what we're going to do today
yeah tuck explains that SERC scientists collaborate with other
scientists as well as the fisheries and waterman to help assess what factors are
affecting the crab population
now the environment is extremely variable so one data point isn't
sufficient for a scientist you have to take lots of data points but we have lots of
data yeah we have not only lots of data points this year but over the last 35
years before we started taking our data a long time ago here
we didn't know a lot about blue crabs and what they did in the average day
now we know tremendous more about blue crabs and their biology but there are still
unknowns and how the complexities of climate change of fishing of habitat
degradation of other predators in the system
disease all these different things are interacting SERC focuses its
research on capture and release studies collecting snapshots of data about the
blue crab populations
why don't we get set up and we can see some crabs and we'll see crabs I hope
I hope so too
ok Josh let's launch the net
all right what do I do throw the float chuck it yeah go ahead today we're using a large net
called an otter trawl it has heavy weights which helped keep it open as it
travels along the bottom of the water being pulled by the boat we'll fish for
about ten minutes which is a fixed distance we know how wide the net is open
and how long that is
we can estimate the abundance of crabs per square meter
of trawl ok to get a long-term picture of crab populations scientists trawl 30 times
a year using the exact same trawling technique
the trawl Net spreads out along the bottom just along the sediment so that it
can collect the benthos or community of creatures that live along the sea bed
after a set time the net is brought into the boat where all the fish and
invertebrates are identified measured and counted
because crabs are solitary and not evenly distributed
scientists must take samples at many locations trying to get an accurate
estimate of the population
if you get any crabs or anything shake them down once the net is in the catch is
released into a bucket for sorting we then separate the crabs from the fish we
begin collecting data on each crab
while the others record data on the fish beautiful creatures
it's called beautiful swimmer scientific name is callinectes sapidus so why are they called
swimmers wait beautiful swimmer or beautiful swimmer that tastes good
I've heard it both ways let's tag them ok we're measuring the crab's shell length from
point to point
its sex and maturity and noting its physical condition
140
ok
that's right 140 as part of a capture and release study we attach a
SERC tag to some of the crabs
wrap three times around on the point make them tight
does that seem ok yeah and then do the same thing on the other side
be sure that it pulls it taut across the carapace of the crab
it's tricky I do appreciate that this little guy is being very patient not
saying anything
I think he knows that I've eaten a lot of his brethren each tag is secured to the
crab's shell and has an ID and phone number
there's a monetary reward for catching the crabs between 1 to 50 dollars
perfect
all right be free
there you go
once the tagged crab is released anyone who catches it can call to report when and
where it was caught this helps scientists track the crabs' movement using combined
data from the trawls and capture release study scientists have discovered that
blue crab populations have severely declined what can be done to help the
crabs
there are many factors impinging on blue crabs but one that we have the most
control over is fishing because we're responsible for the fishing is it
possible for the population of blue crab to recover
yes the challenge of monitoring blue crabs and fish is that the bay is very
large and stretches over many states the states must work together to create laws
to protect and monitor their fisheries Waterman must also still be able to make
the living with your Waterman you can't just stop having any
income for a year or two years but if you can back off on the fishing pressure
the population will recover
blue crab have great reproductive potential and so there's good hope with
good management that we can have a sustainable fishery as for our original question
how do scientists track and monitor blue crab populations in the Chesapeake Bay
using capture and release and trawling scientists can assess the population of
blue crabs in the Chesapeake Bay which can provide vital information to states
and fisheries managers studying blue crabs and crab management is complex due
to the size of the bay and the many interests involved