We are mapping and determining where critical fish habitat is in a particular area off the
coast of North Carolina in what’s known as a Wind Energy Call Area. It’s an area
that the government agency, the Bureau of Ocean Energy Management (or BOEM), has designated
as a place where future wind energy development may occur. So, it’s a place where they would,
perhaps, put turbines in the offshore environment.
The Wind Energy Area that we’ve been working in is off of Wilmington, North Carolina. It’s
about fifteen miles off of Cape Fear. It’s one of three wind energy areas off North Carolina.
There’s another that is just west of Wilmington-East, called Wilmington-West. And then, there’s
a third area off the northern Outer Banks that is called Kitty Hawk.
We are looking for habitat that’s what we call hardbottom. These are areas that are
either consolidated sediment or exposed outcroppings of rock. Sometimes they are man-made structures,
such as historic shipwrecks, and these areas form important habitat for fish, as well as
critters that you sometimes see on coral reefs, so, invertebrates and macroalgae. Some of
them are these incredible ledge features that are up to 30 feet or 10 meters tall. Other
ones are kindof like a parking lot; they’re flat and don’t have much relief.
Hardbottom sites are critical habitat for fish because they function as places where the fishes can
forage. They can seek refuge from predators in the nooks and crannies in these habitats.
They’re also something that we call nearshore connectivity corridors, where fish can move
from areas in the estuaries to offshore reefs using these as stepping stones.
I think that people would be amazed at the types of habitats we have offshore of North
Carolina. They vary from the tropical reefs, or what seem like tropical reefs, to vast
tracks of sand that don’t appear to host any biological life whatsoever, what we might
call an ocean desert. What impresses us greatly when working offshore of North Carolina are
the diversity of fishes that occupy the hardbottom habitats. Those are the ones that we think
might be some of the more sensitive habitats offshore. And, we have very little understanding
of where those habitats are located. Fishermen know where they are. They fish those areas
all of the time, and we’ve been learning a great deal from the fishermen on where these
habitats are located. That gives us a bit of information on where they are, but we still
have a limited understanding of how these habitats are structured offshore. Are they
clustered in one area, or are they randomly distributed across the entire coastline of North Carolina?
We have a pretty good understanding of how these hardbottom habitats support the fish
that are important to our economy and ecology. If BOEM is interested in reducing the potential
environmental impacts from, say, developing a wind farm off our coast, we wish to conduct
some studies to point them to where these habitats might occur, where these most sensitive
areas might occur, so that those areas can be avoided in terms of development and potential
environmental impact.
What it comes down to is that we would love to get eyes in the water everywhere that we
go offshore of North Caronia, and in 277,000 acres that would just be physically impossible,
so we must use remote sensing tools to give us an image of what the seafloor looks like.
Two of the ways that we did that in the early stages of this project were using sidescan
sonar and multibeam sonar. Sidescan sonar gives us about a 300-meter swath or a thousand-foot
swath of the seafloor that shows us the texture of the seafloor, how hard is the seafloor.
It can show us different types of sediment or give us an indication of the type of sediment
that are on the seafloor. The multibeam sonar, on the other hand, gives us an image of the
topography or the relief of the seafloor. It gives us the elevation like you would see
on a Google Earth map. We put those pieces together, and it gives us both the texture,
the hardness and roughness, and then the elevation of the seafloor, and that gives us an indication
of the types of habitats that might occur. We then use divers to validate and ground-truth
what the sonars are telling us. The imagery that we’re gathering using the sonar and
from our divers are putting together a really interesting picture of what these habitats
look like from a digital sense and then helping us interpret from a biological sense, using
our eyes, what those habitats are really like.
One of the things that we do while underwater on our diving surveys is count the fish. And,
we set out this 30-meter long transect tape. It is basically an underwater measuring tape,
and we swim along that tape and count the fish that we see. We record what species they
are; we estimate their length, and we can use that information to identify which habitats
are the most important fish habitat.
In coral reef systems, it’s well known that when you have a more structurally complex
habitat, the fish diversity, the abundance or the number of fish, will increase. But,
nobody knows if that relationship is the same here off the coast of North Carolina. And,
if we can understand whether these complex habitats may be better fish habitat, we can
use that to identify which areas are most critical to conserve and protect in the long run.
Hardbottoms are really important for the residents of North Carolina because they support so
many fish that we depend on, both for recreational and commercial fisheries. They also support
a vibrant recreational diving community and tourism. And, overall, they are really important
for the health of our ecosystems because they provide nursery habitat, places where fish
can eat or forage, places where they can seek refuge, and also corridors to help them move
from inshore to offshore locations. So because they perform all of these functions, they
are really important for us to conserve and protect.