Studying fishes of the deep waters
of the Gulf of Maine, like ecologists study
animals on land, is an exercise that requires
more than binoculars and a notebook. Using occupied
submersibles and remotely operated vehicles
to go to work, scientists supported by the NOAA's
Undersea Research Program (NURP) venture beneath
the cold and turbid waters of the Gulf to understand
how fish interact with a myriad of other seafloor
species and geological structures which can
enhance their survival.
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...fishing gears such as trawls and dredges
impact seafloor habitats by reducing complexity and altering
communities of animals that live on and in the seafloor.
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The Gulf of Maine and Georges Bank have supported
fishing for over 400 years. From the time that Basque fishermen
ventured far beyond their European shores, the waters of this region
have been known as some of the most productive in the world. To
all who saw the bounty of this part of the ocean, there seemed to
be an endless supply of fish. It was not until the last half of
the 20th century that the limitations of the ocean became obvious.
While there have been extensive efforts to study responses of overexploitation
on fish populations, relatively little work has addressed the role
that habitat plays in enhancing the survival of individual animals
in outer continental shelf environments. Further, while we struggle
to understand how habitat features affect fish populations and communities,
fishing gears such as trawls and dredges impact seafloor habitats
by reducing complexity and altering communities or animals that
live on and in the seafloor.
A haddock uses a boulder for cover from predators and current.
Photo courtesy of Peter Auster and Paul Donaldson, North Atlantic
& Great Lakes Center, NURC/University of Connecticut.
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Fish such as Atlantic cod, haddock, Acadian redfish,
and spiny dogfish are at very low population levels. Species like
redfish have not fully recovered from overexploitation in the 1960s.
Their recovery may, in part, be impeded because their habitats have
been destroyed by fishing gear. Just as some animals take refuge
in the African prairie grass to shelter from lions, some marine
fish take refuge in places like boulder reefs, anenome forests,
worm tube mats, sponge-covered gravel, and complex mud burrows to
hide from bigger fish.
Peter Auster, Science Director for the NURP
Center at the University of Connecticut, has been studying the
ecology of fishes, primarily those of the outer continental shelf
and beyond, for over 15 years.
Launching the Kraken ROV from the RV Connecticut.
Photo courtesy of Peter Auster, North Atlantic & Great Lakes
Center, NURC/University of Connecticut.
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He and his colleagues have used submersibles and ROVs
to collect data on the distribution, abundance, and behavior of
fishes in relation to the underwater landscape. Underwater video
is the primary way data are collected.
Using parallel laser systems to continuously calibrate
the area viewed by the video camera and as a way to measure fishes,
what was once a qualitative way of recording what scientists see
is now a quantitative tool. "Submersibles and ROVs allow us to conduct
the same types of studies on fishes that my colleagues who study
terrestrial animals have been able to do by walking out into meadows,
forests, and deserts," said Auster.
However, the field studies are only part of the picture.
"The field work gives us information on the patterns of habitat
use by the animals of interest," said Auster, "but the story does
not end there." The researchers then take the results of the fieldwork
to design laboratory studies and computer models which apply their
research results at the geographic scales of fish populations and
communities. "Laboratory experiments allow us to study how differences
in habitat features affect rates of survival and escape behaviors",
said James Lindholm, a Post-Doctoral Fellow in Auster's lab. For
example, their studies of juvenile cod link survival of young fish
to patterns in the types of invertebrates that grow on the seafloor.
Cerianthid anenome forests and dense sponges provide complex
habitat for fishes.
Photo courtesy of Peter Auster and Paul Donaldson, North Atlantic
& Great Lakes Center, NURC/University of Connecticut.
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Survival was greatest when "sponge"
habitats were present, in contrast to bare cobble
and sand. The data from both field and laboratory
are then used to construct computer models that
demonstrate how fish populations are affected
by habitat change. The results of studies on
cod showed that when adult populations are high,
habitat changes had little effect on juvenile
survival and overall population dynamics. However,
when adult populations are low, habitat changes
had a large effect on the survival of juveniles
and overall population structure. The results
suggest that managing seafloor habitats, as
well as populations of fishes, may be the path
towards sustainability. Further, the work suggests
a direct link between biological diversity and
the sustained production of species we want
to exploit by fishing. "Everywhere we look",
said Auster, "we see relationships of fishes
with various types of habitats which are composed
in part by other organisms such as sponges and
anenomes." "We need to take lessons from those
managing wildlife on land - we need to be worried
about all of the parts of the environment that
support the species we want to exploit as well
as conserve."
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