>>NARRATOR:
The Florida Everglades.
Beautiful.
Vast.
Harsh.
Remote.
>>It is a huge wetland
that flows across most
of southern Florida,
and then it runs into the ocean.
>>NARRATOR:
Some of North America's
fiercest predators live here,
including the American alligator
and the bull shark.
>>They're top predators.
They eat a lot
of different types of prey,
which means they could have
a big impact
on a lot of different
prey populations,
which then could have
cascading effects
down to lower levels
of the food chain.
>>NARRATOR:
Despite its wild nature,
the Everglades is an ecosystem
in trouble.
For nearly a century,
man drained the swamp.
Now, a large-scale
restoration project
aims to return the wetland
to its former glory.
>>More and more fresh water
is going to come in,
so it's really important
we get the water right
and we know how animals like
sharks and alligators respond
so we're managing the ecosystem
right for them.
That's why we're doing
these studies--
to get an idea
and make predictions
about how this change
will affect the ecosystem,
so we can protect those animals
and make sure they fill
that critical ecological role.
♪♪
>>Major funding
for this program
was provided
by the Batchelor Foundation,
encouraging people
to preserve and protect
America's underwater resources.
And by Divers Direct,
inspiring the pursuit
of tropical adventure
scuba diving.
>>NARRATOR: On the southern tip
of the Florida peninsula,
the Everglades meet
the Gulf of Mexico.
Here, the river of grass
gives way to a maze
of mangrove-lined rivers that
eventually flow into the sea.
>>The Shark River estuar
is the terminus
of the Shark River Slough,
which is a major part of the
central and southern Everglades.
That is the main conduit
of fresh water
out of the Everglades
and into the Gulf of Mexico.
So the Shark River is
a really important place
where fresh water from the north
and salt water from the Gulf
of Mexico mix together,
and we get this really
interesting mix of organisms.
>>NARRATOR:
Recognized as a wetland
of international importance,
the Everglades ecosystem
is a unique place.
>>There's a huge abundance
of life here.
It's one of those
wilderness places
that are few and far between
on the planet now,
but it's also a place that's
affected a lot by humans.
>>NARRATOR: Over the course
of the 20th century,
humans have greatly changed
the way water flows
across the Everglades.
Canals and dikes were built
to provide flood control
and deliver fresh water
to agricultural operations
and South Florida's
ever-growing human population.
This greatly decreased
the amount of fresh water
flowing across the Everglades.
>>That fresh water that's
the source of life
for this part of the Everglades,
the tap's kind of been
turned off.
>>NARRATOR: The impacts on
the natural system were severe,
and now a multibillion-dollar
restoration project is underwa
to return some of that water
back to the Everglades.
>>As we re-engineer the water,
we need to figure out
how the plants and animals
are going to respond
so we don't muck up
the ecosystem even worse.
So really understanding how
important different species are,
how they respond to the water
and other conditions
is critical for getting
the restoration right.
>>NARRATOR:
To better understand
the various ecological roles
species pla
in the coastal Everglades,
Mike Heithaus and his team study
predator-prey interactions
and how predators respond
to changes in the environment.
>>So a lot of the work we do
is trying to figure out how
humans affect this ecosystem,
and as we try to restore it,
how that's going to affect
the big predators like
alligators and sharks.
>>NARRATOR: To do so,
scientists want to know
where the animals are found
and why.
During the daytime,
they try to catch bull sharks
in different parts
of the Shark River.
>>We have four different areas
within the estuar
that we set lines that typically
have different conditions--
mainly differences in salinity.
And so we set the lines
at a salinity gradient,
starting from the ocean
all the way up to the freshwater
marshes and in between.
>>NARRATOR:
Using the number of sharks
caught in different locations
and at different times
of the year,
the scientists can determine
the types of areas
and conditions the animals need.
>>When we first came out here,
we were told there's no way
you're going to find sharks.
We set our lines and had two
sharks on our very first one.
>>NARRATOR: Bull sharks
are the only species of shark
in North America that can live
in fresh water,
and the juvenile sharks usually
live in rivers and estuaries
until they are big enough
to move to the ocean.
>>To catch bull sharks,
we use long lines
with baited hooks with mullet,
and those sit on the bottom
for about an hour.
So the long lines have about 50
hooks, and we allow them to soak
to attract any sharks
that are in the area.
And we also use drum lines,
which have larger hooks
and larger bait
to catch large predatory sharks
that may feed on the juvenile
bull sharks
to quantify the risk
of predation
that they have
in different areas.
>>Oh, little shark!
This is a little, little guy.
>>After we catch a shark,
we take length measurements...
>>55, 62.5, and 78.
>>...weight measurements.
>>Four kilograms.
>>We put an external
identification tag in them
so that if we recapture them,
we can determine how much
they've grown
and if their body mass
has changed.
>>Identification tag
j-1-0-6-4-1.
>>That's the umbilical scar,
and it takes a couple of months
for that to heal,
so when we see that,
we know that this shark
is relatively newborn,
definitely less than
one year old.
>>NARRATOR: The scientists
are also interested
in studying the diets
of the sharks
using a method called
stable isotope analysis.
>>It's based on the idea
that you are what you eat.
And so carbon and nitrogen are
common elements in our bodies,
and we can look
at different forms
of those carbon
and nitrogen isotopes
and look at their ratios.
And so what happens is that
plants have different values
for their carbon
whether they're plants in the
ocean or plants in fresh water.
>>NARRATOR: When animals
eat plants or other animals,
these carbon values stay roughly
the same.
So by analyzing the carbon
isotopes in a shark,
scientists can tell
whether it has fed in food webs
from the ocean
or from fresh water.
The nitrogen isotopes
in its bod
show how high in the food chain
the animal eats.
Different tissues
in the animal's body reflect
what and where an animal has
eaten over various time periods.
>>Fin tissue
turns over the slowest,
and it takes about
a year-and-a-half to two years
for that tissue to be replaced,
so it's a very long-term
estimate of their diet.
The muscle tissue takes
about a year-and-a-half
to be replaced,
so that's another
long-term tissue that we use
to look at their diet.
And then blood,
we look at whole blood,
which is just the blood
extracted from their veins,
and that turns over in
about a year,
so that's kind of a mid-range
estimate of their diet.
And then we actually separate
the blood
and extract the plasma,
which is replaced relatively
quickly, and that provides us
with a short-term estimate
of their diet.
And that actually allows us
to look at seasonal changes
or actually changes
in their diet based on size.
We have caught sharks all the
way up at the top of the river
about 20 miles from the ocean.
So there are sharks everywhere
within the estuary.
When they're born,
they're typically only eating
estuarine and freshwater fish
and other species,
and as they grow, they're
starting to eat more animals
from marine food webs.
>>NARRATOR:
To expand their data,
the scientists also outfit
the juvenile sharks
with acoustic transmitters.
>>So the long-lining
allows us to determine
which areas have more sharks
in them.
However, it doesn't give us
a fine-scale estimate
of what the sharks are doing
in between the time
when we set these lines,
and so we acoustically tag them
and passively monitor
their movements
so we can know
what they're doing
while they're in the estuary
until they leave.
>>Come here, little cutie.
There we go.
>>For a lot of shark species,
when they're turned
on their backs,
they go into a more
relaxed state.
This allows us to do
the surgeries,
to insert the acoustic
transmitters into them
without the sharks
thrashing around too much.
The transmitters emit
a unique frequenc
that's recorded by the receivers
when they're within
their listening range,
and the battery life is up
to three years.
>>So these acoustic
transmitters,
they send out
an ultrasonic ping randoml
every 60 to 120 seconds,
and the ping is a unique code.
And then those pings
are heard by monitors
that we have stationed
throughout the Everglades,
and those monitors have ranges
of up to 1,000 meters.
The monitor will record
the date and the time
and the individual
that was there.
>>And they're arranged
in a pattern
such that they're paired,
so we can determine not only
the location of the sharks,
but the direction that
they're moving in.
>>NARRATOR:
Since 2006,
the scientists have caught
nearly 300 sharks
and have acoustically tagged
more than 60.
>>This project is ongoing
and a long-term project,
and we are interested
in how the change in abundance
varies annually,
and try to correlate that
with changes in things
like temperature, rainfall,
and the dynamics of the seasons.
So we pulled up our monitor
over here from the water,
and it has picked up
more than 12,000 detections,
so that's really good.
>>NARRATOR: Over time,
the research has revealed
some astonishing information.
The juvenile bull sharks
live away from the ocean
to be safe from larger sharks
that could eat them.
Some individuals, however,
are willing to take risks
for a meal.
>>They might go
from these freshwater areas
down to the ocean
and back again.
There might be more food
down at the ocean,
but you have to run the gauntlet
of big sharks to get there.
So a lot of individuals
are not willing to risk
getting eaten by a bigger shark
to go grab a meal.
Others, for some reason, are.
We're trying to find out why.
If you don't understand
the patterns of specialization
within individuals,
you can't develop particularly
effective conservation
and management plans.
>>Gorgeous.
>>NARRATOR:
Another top predator
at home in the Everglades
is the alligator.
Its behaviors could also provide
clues to the scientists
on how changes
in freshwater levels
might impact the ecosystem.
Currently, freshwater levels
in the Everglades
can vary widely between seasons
and from year to year,
creating a "natural experiment"
that helps experts make
predictions about the future.
>>We're trying to figure out
how they're behaving now,
under the current
water management system,
to predict how those behaviors
are going to change
in the future,
and then predict how
the Everglades as a whole
might change in the future
in response to that, as well.
>>NARRATOR: As with sharks,
the experts want to know
where the alligators go
and what they eat.
But to track
the animals' movements,
scientists first need
to catch the large reptiles.
>>Tell me when we're
on top of him.
>>Okay.
Slow, slow, slow, slow.
>>We go out at night
because it's easier to find them
at night.
And we use spotlights
to find their eye shine,
because their eye lights up
a really bright red.
>>Gator straight ahead.
>>I see it.
>>Oh, it went under.
>>Persistence and patience.
>>Okay, got one here,
And there's another one
up there, too.
Got two of them right here.
>>And then we approach them.
We have these long poles with
snares around the end of them
so we can slip it around
their neck and snare them.
(loud splashing)
>>So what do you say,
the biggest we've caught
by a good few pounds?
>>Possibly.
>>We have an easier time
catching the alligators
the bigger they are,
because they are less wary.
They are used to being
king of the hill,
whereas the smaller alligators
are a bit little more jumpy.
Alligators are cannibals, so the
smaller juvenile alligators,
they need to be scared
of bigger things,
whereas those big alligators,
they've been large for so long,
they don't care.
>>NARRATOR: Before the
alligator is brought on board...
>>Yeah, you don't like me
at all.
Hiss, hiss, hiss.
>>NARRATOR: ...its mouth
is taped shut as a precaution.
>>That's enough.
>>NARRATOR: While an alligator
can chomp down fiercel
on its prey,
the muscles that open its mouth
are rather weak.
>>So you can actually hold
an alligator's mouth shut
just with one finger
just pressing down,
and they don't have the power
to open it.
It's the closing power
you've got to be afraid of.
>>NARRATOR:
To study their diet,
scientists take blood
and skin samples
for stable isotope analysis.
>>So we take the skin sample
from what's called the scutes.
It's kind of the ridges
that you see
as you look
at an alligator's back.
So I clip a small piece
of the scute
off of the back of the tail,
and we do that because
that's the easiest place
to get a skin sample,
and it also doesn't hurt them
because they don't have
any nerve endings
in the tops of those scutes,
so it doesn't bother them.
>>Lift, lift, lift, lift.
>>NARRATOR: Next, a gator
is weighed and measured,
and an external tag
is attached to its toe.
>>It's a little metal tag that
has a five-digit number in it.
And so if anybody
anywhere in the state
catches that alligator again,
they can say, "Okay,
where was it originally tagged?"
And we can learn about
their movements and behaviors
in that way also.
>>NARRATOR: To track
the alligators' movements
within the estuary,
they too are outfitted
with acoustic transmitters.
>>What I do is I attach it
to the external part
of the tail.
So I drill holes
in the scutes,
and again, they don't have
any nerve endings
in that part of their body,
so it doesn't hurt them.
Then we thread some stainless
steel wire through the scutes
and also through
the transmitter.
The wire keeps the transmitter
in place on the tail,
and then we cover it
with a marine-grade epox
that'll set underwater.
And the other half.
So it'll keep that whole thing
in place
and also streamline
the attachment.
Okay, that's looking good.
For my study,
I only track adults,
and adults in the Everglades
are considered
basically six feet or bigger.
The average size
of animals we catch
is between six and eight feet.
The biggest we ever caught
is nine feet.
In other parts
of the alligators' range,
they will grow bigger--
they'll grow to 12, 13, 14 feet.
That's because they have
much better food to eat,
so it enables them to grow
faster and bigger.
One of the first alligators
I ever tagged
I'm still getting
data from today.
So I've been tracking
this alligator
for four-and-a-half years,
roughly.
>>Right there, right there.
>>We've caught
over 100 alligators.
We've attached tracking devices
to 52 of them.
I got him, I got him, I got him.
I got him.
>>NARRATOR:
In addition to taking
blood and skin samples,
Adam has also analyzed
the stomach contents
of about 50 alligators
to learn more about their diet.
>>So right now, we are
immobilizing his arms and legs
so we can transport him
without fear of him climbing
out of the boat.
The duct tape
that we're putting on
will protect them
from hurting themselves and us.
>>One, two, three.
>>NARRATOR: Taking the stomach
contents from an alligator
is similar to a person
having his or her stomach pumped
at the hospital.
It is the least invasive method
for scientists to collect
this critical information.
>>So that's one
of my favorite parts.
We strap it
to a long wooden plank
with duct tape and with straps
to make sure that
it can't move too much,
because it's really not
for our safety,
it's for its own safet
because if it moves during this
process, it can hurt itself.
So we strap it to the board.
Then we angle the board so that
the head is pointing down,
and then we take the tape off
of the mouth
and it instinctually
opens its mouth up.
Oh, hello!
And then we take a PVC pipe
and we place it in the mouth.
Whew!
Hello, sir.
The pipe is strong enough
that it doesn't break
in the alligator's mouth.
So the pipe is basically holding
the alligator's mouth open.
And then we tape the mouth
around the PVC
so that it can't also open
its mouth any more.
We take a hose that's been
coated in mineral oil,
and I stick the hose
through the PVC pipe
that's in the mouth
and down through the esophagus
and into the stomach.
Ooh, that smells lovely.
There we go.
That's disgusting.
And then
once it's in the stomach,
I turn on a pump that fills
the stomach with water,
and then we do sort of a gentle
Heimlich maneuver motion
to massage the water
and the food out of the stomach
and out of the mouth
and into a waiting bucket.
Definitely feathers.
>>More?
>>Yeah, keep going.
Yeah, yeah, I feel some chunks.
Oh, yeah.
Uh-huh.
Oh, that smells so bad.
Oh my god, that's really bad.
>>Well, we don't have
a vegetarian alligator here!
>>It's coming out gangbusters,
now.
Here we go.
Oh, look at that,
there are feathers
all the way up in there.
That is awesome.
We find really exciting things.
The most frequent thing we find
is blue crab parts.
We've also found crayfish,
we've found shrimp,
lots of tiny little fish,
which was surprising.
I was expecting to find them
eating big fish,
like a gar or a snook
or something of that nature.
We've also found turtle parts,
other alligators,
and one of the most
interesting things we found
was pond apple seeds.
So there are these fruits
called pond apples,
and most people don't think that
alligators would eat a fruit.
They think that they're
strict carnivores.
In some alligators, we found
up to four or five pond apples.
And so that was a very
exciting find.
>>These big reptiles
with huge mouths and big teeth,
the fact that you find
little fish, pond apples
and crabs came as a very big
surprise for us.
It's hard to say exactly why
they're doing it.
One thing is that it's probably
what's easy to catch.
You might be really big,
but it's hard
to catch a gar or a snook
or a big fish,
but it's a lot easier
to catch small fish.
Pond apples don't run away
very well,
and the crabs are
pretty abundant here
and are also easy to catch.
Yummy raccoon?
>>May be yummy raccoon.
That's what my money is on.
>>But we also know that
when they get a chance,
they will go after big things,
so you find mammals and birds
in them,
just not as many as we thought.
Ready?
>>I'm going to drop
my end in first.
One, two...
>>The thing about
the alligators is that
they have very limited
food sources here.
It's a very nutrient-poor
environment.
>>There's the tape.
Most estuaries are just
teeming with life
because the nutrients
from the fresh water
hit the nutrients from the ocean
and things go crazy.
But here, as that fresh water
moves slowl
through the Everglades, most
of the nutrients get sucked out.
>>There's just not a lot
of food for them.
>>NARRATOR: The scientists
weren't just surprised
by what the gators were eating,
but where some of them went
to feed.
>>They travel
between the freshwater
and the saltwater environments.
Some individuals will do it
very frequently.
These alligators
would make upwards
of a 30-kilometer roundtrip.
So they would travel
15 kilometers
from fresh water to salt water,
and they would stay in the salt
water for about a day or so,
and then they would turn around
and come back after a day,
so they would be making
these roundtrips
every three or four days,
and they would do it repeatedly.
In one wet season,
which lasts about six months,
there was one alligator
that made about 50 trips.
>>When Adam tracked that first
alligator down to the ocean,
we had some people sa
our equipment must be
malfunctioning.
But by studying these animals
with different technologies
and across many years,
Adam has found that probably
a third of those alligators
are commuters.
>>NARRATOR: This was a very
unusual discovery.
>>Alligators are thought to be
strictly freshwater species
and that they can't survive
in salt water
for very long periods of time.
And we have found
that similar thing,
but we found that they will
choose to go into salt water,
and that was a very
interesting finding.
So why would they choose to go
into a salty environment?
And we think that the answer
is that
there must be more food there.
So they're trading off food
for a little bit of stress,
but then they come back
into fresh water
to sort of even out
their salt load again.
If it drinks the fresh water,
then it can expel
the extra salt from its body.
The stable isotope analysis
of their tissues showed that
the alligators that were
traveling down to the salt water
were traveling there to feed.
The individuals that did not
move down to the salt water,
they had isotope values
indicative of the freshwater
food web.
>>NARRATOR: Now, scientists
are trying to determine
if the sharks and alligators
which feed in the ocean
are excreting those nutrients
upriver.
>>In a system like this,
where you have generally
low nutrients,
a little bit of nutrient
coming in can have a big impact.
The question for us now is,
is it enough nutrient
coming upstream
from alligators and sharks
to have a big impact?
And that's a tough question
to answer,
but it's one that
we're trying to work on.
>>NARRATOR: During their
research, Mike, Adam and Phil
have made some really
surprising observations.
>>One of the neatest is that
we find out that these predators
are really individuals.
You can't just see
an alligator and say,
"Oh, it's an alligator,
it does what all
the other alligators do."
They kind of have their own
behaviors, almost personalities.
This is one of the things
that's really exciting to me is
learning more about why are
animals doing what they do,
and then how does that affect
their role in the ecosystem?
So it's really important that
we learn more
about the behaviors
individuals displa
to really understand
their ecological roles.
So here in the Everglades,
some of these more
stay-at-home animals
probably have a very different
role in the ecosystem
than the ones that commute
down to the ocean.
>>NARRATOR: Figuring out
how to properly redirect
the fresh water
back into the Everglades
is not an easy task.
>>If we put the water in
in too big of a burst,
we might see animals
get pushed out of the system
to areas where they don't
survive very well.
So we have to be sure
that we're mimicking
the natural pulses
of fresh water.
One thing about the Everglades
is that
things are changing
almost constantly.
We have wet seasons,
we have dry seasons,
so the amount of fresh water
coming in varies that way.
But we have wet wet seasons,
we have dry dry seasons.
We have wet dry seasons.
So by looking across many years
and many seasons,
we can get an idea
of how fresh water
affects sharks and alligators.
So it requires long-term studies
to really figure it out,
and that's one of the exciting
things about this project is
we've been at it long enough
that we're starting
to get an idea
of how these animals respond
to changes in their environment.
The challenge for managers isn't
just getting the water right
for alligators and sharks;
it's for all of the other
organisms here, as well.
♪♪
>>Major funding
for this program
was provided
by the Batchelor Foundation,
encouraging people
to preserve and protect
America's underwater resources.
And by Divers Direct,
inspiring the pursuit
of tropical adventure
scuba diving.