[VIDEO LOGO]
In this episode, we ask the question,
how do scientists use electricity
to study fish populations?
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Hey, Josh Bernstein here.
I'm on the Patuxent River in Eastern Maryland.
I've come here to learn about this guy, the blue catfish.
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Blue catfish are native to the Mississippi, Missouri,
and Ohio River basins.
They can grow to more than five feet in length
and 100 pounds in weight.
Blue catfish are an invasive species because the bay is not
their native home.
They have no natural predators, eat
large amounts of native species of fish and invertebrates,
reproduce rapidly, and have the potential
for economic and environmental harm.
I'm visiting with researchers from the Smithsonian
Environmental Research Center to learn more.
I'm meeting with Rob Aguilar.
He has offered to show me how scientists
solve the challenge of capturing and monitoring blue catfish
populations in the waters of the bay.
Because the catfish live in murky water of varying depths
and they move around the bay, it's
challenging to capture them.
One technique Rob and his team employ is electrofishing.
Electrofishing started when?
It's been around for several decades.
It's a really efficient, safe way
to sample fish in low-salinity environments
where other methods just are impractical.
But electrofishing allows you to get
a good idea of the assemblage of fish
or specific species of fish that you're looking for.
Electrofishing uses an electrical current
measured by frequency to stun the fish so that they
float to the top of the water.
With the catfish, we are using a lower frequency
than you would if you wanted to assess the total fish
community.
The blue catfish are very responsive
to this low frequency.
So when we're fishing today, we should just
see the blue catfish responding really well to the current
that we apply to the water.
The electrical current is run through the water where
the fish live, which can be dangerous
if it's not done properly.
I'm wearing this so I don't get electrocuted.
And you're going to stay far away
so you don't get electrocuted.
Electrocution can pose a serious risk,
which is why I had to complete an electrofishing safety
course in order to join Rob in this endeavor.
I should also point out that electrofishing without a permit
is illegal.
So please do not try this at home.
Having said that, electrofishing is pretty amazing science
in action.
On the boat, a generator connected to a special control
box creates a current.
One side is connected to the boat, which
acts as a large single cathode.
Off the bow, two anodes dangle into the water.
The electrical current travels through the slightly saline
river.
Everything 100 feet around us will
feel this charge, including people in other boats.
So we must be very careful.
Rock and roll?
Indeed.
We're about to turn the generator on.
It's going to get noisy here.
And more importantly, we're about to electrify this region.
So you are going to move away, about 100 feet.
It's for your own safety.
We're live.
We're fishing.
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Within seconds, blue catfish starts
floating up to the surface.
There's one.
My job in the bow is to spot the fish, point them out to Rob,
and net them.
Got one.
In the stern, Rob steers us towards the fish.
What's fascinating to me is how effective electrofishing is.
The frequency of the charge Rob sends into the water
is truly species specific.
Only the blue catfish are floating to the surface.
The other fish can swim away.
It's pretty wild.
The second the current hits the water, boom, the fish come up.
It's crazy.
Despite appearances, these fish are not dead.
They're just stunned, which makes it easy
for me to scoop them up and drop them into a tub of water
on the boat.
This is like cheating when it comes to fishing.
By sending an electric current into the water,
Rob and his team can capture and monitor
a single species of fish and its population.
This is important because the invasive catfish now makes up
over 75% of the total fish biomass
or weight in parts of the bay.
This has consequences for the whole bay's food web,
especially the fish, oysters, clams, and crabs they feed on.
As for our original question, how
do scientists use electricity to study fish populations?
We can see that electrofishing offers
a practical and efficient way to catch invasive species.
Rob says we have enough fish, so it's
time to take them for tagging with an acoustic tag and dart
ID tag.
Onto part 2, catfish surgery.
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