Posted
20th August 2001
Over Fishing = Extinction
By
Cat Lazaroff
WASHINGTON, DC, August 14, 2001 (ENS) - A new study identifies
overfishing as the cause, historically and currently, of many
of the problems facing coastal ecosystems today. Researchers
linked the ecological extinctions of marine megafauna - vast
populations of whales, manatees, dugongs, monk seals, sea turtles,
swordfish, sharks, giant codfish and rays - to overfishing at
a global scale never before realized.
Recognition of what has been lost, however, also shows what
could be gained. The scientists claim this revolutionary historical
perspective is essential to wildlife management because historic
data provide a framework for restoration that is otherwise invisible.
"Successful management and restoration of coastal marine ecosystems
has failed in part because of a lack of understanding the deeper
historical causes of collapses in these ecosystems," said Dr.
Jim Estes, a U.S. Geological Survey research ecologist with
the Western Ecological Research Center, one of the authors of
the article. "Every marine ecosystem I have ever studied during
my entire 30 year career looks unrecognizably different from
the way it used to be, and I wanted to know why," added Dr.
Jeremy Jackson of Scripps Institution of Oceanography in San
Diego. Jackson, a renowned marine ecologist, instigated the
two year study of human impacts on oceans over time.
Jackson convened an international team of 19 leading marine
researchers at the National Center for Ecological Analysis and
Synthesis (NCEAS) in Santa Barbara, California. Drawing on paleoecological,
archeological and historical data, the scientists uncovered
past evidence of seas teeming with large animals as well as
abundances of oysters and shellfish so vast they posed hazards
to navigation. The scientists examined records from marine sediments
dating from about 125,000 years ago; archaeological records
from human coastal settlements occupied after about 10,000 years
ago; historical records from documents of the first European
trade based colonial expansion in the Americas and South Pacific
in the 15th century to the present; and ecological studies from
the past century to help calibrate the other records. They found
that the three cultural stages they examined - aboriginal, colonial
and global - occurred at different and distinct times in the
Americas, New Zealand and Australia. This enabled the scientists
to distinguish fishing in these locations by cultural stages.
The scientists also were able to determine whether changes occurred
due to human impacts or changing climate. They compared the
function and structure of kelp forests, coral reefs and estuaries
before and after fishing occurred.
The scientists found that as human disturbance occurred over
time, ecosystem structures and functions changed in response
to overfishing. While few species like the Steller's sea cow
of the North Pacific and the sea mink of the Gulf of Maine were
fished to extinction, many became ecologically extinct like
the sea otter, which did not make a comeback from intense exploitation
until afforded protection in the 20th century. "Ecological extinction
caused by overfishing precedes all other pervasive human disturbance
to coastal ecosystems," begins the study, published in the July
27 issue of the journal "Science." The scientists also found
when multiple species occupied similar niches in an ecosystem's
structure and could fill a similar function of an overfished
species, signs of overfishing could be masked for long periods
of time. "Comparing the magnitude of the mass ecological extinctions
in the ocean to those on land may not be enough," said study
coauthor Dr. Roger Bradbury of the Australian National University
in Canberra Australia. "On the land, as we killed off the giant
mammals and destroyed the ancient forests, we replaced them
with a new suite of farmed species. In the coastal seas, we
took out animals and replaced them with nothing."
The new data also show that historical overkill of this marine
life triggered current ecological collapses - many of which
have been mistakenly attributed to pollution. "We started out
to study everything that people had ever done to oceans historically
and were astounded to discover that in each case we examined,
overfishing was the primary driver of ecosystem collapse," said
Jackson. The data demonstrate that overfishing triggered changes
in ecosystem structure and function as early as the late aboriginal
and early colonial stages. The scientists show that grinding
down marine food webs is responsible for many of the problems
faced by marine fisheries today.
Removal of key predators and entire layers of the food chain
set off sequences of events that are now culminating in toxic
algal blooms, dead zones, outbreaks of diseases and other symptoms
of ecological instability.
LIVING EXAMPLES
One
example of the negative chain reaction brought on by overfishing
is the Chesapeake Bay, which is now an impoverished ecosystem
dominated by bacteria. Historically, oysters filtered the entire
water column of microscopic bacteria and debris every three
days. Records describe a lost cannon, "clearly visible in over
30 feet of water." Increased runoff from farms and urban areas
have been blamed for many of the Cheseapeake Bay's problems.
But the new research blames instead the mechanized extraction
of the vast oyster reefs. Overfishing the oysters removed the
top down control of phytoplankton. Grey whales - now extinct
in the Atlantic - dolphins, manatees, river otters, sea turtles,
alligators, giant sturgeon and hammerhead sharks were all once
abundant inhabitants of Chesapeake Bay, but are now virtually
eliminated. Other examples include the overfishing of large
fish, which has led to overgrowth of algae on coral reefs, smothering
the reefs and jeopardizing the approximately three million species
that they harbor.
The recent die off of turtlegrass beds in Florida Bay can be
attributed to the ecological extinction of green sea turtles.
Overkill of the green sea turtle and other seagrass grazers
such as dugongs and manatees has contributed to outbreaks of
disease and die offs in seagrasses. Scientists have also long
suspected that overfishing has caused the well publicized collapse
of sea lion and sea otter populations in the Bering Sea. New
research suggests that vast depletion of the great whales by
humans has also contributed to this collapse. Whaling and overfishing
forced killer whales to switch prey from the great whales to
sea lions and most recently to sea otters. Without sea otters
to prey on sea urchins, populations of sea urchins have boomed,
destroying kelp forests and other marine habitats.
The researchers warn that responding only to current events
on a case by case basis cannot solve the ocean's problems because
impacts of human disturbance are synergistic and have deep historical
roots. Ecological extinctions make ecosystems more vulnerable
to other natural and human disturbances such as pollution, disease
and climate change. Instead, the scientists say, problems need
to be addressed by a series of bold experiments to test the
success of integrated management on the scale of entire ecosystems.
With few exceptions, such as the Steller's sea cow, and Caribbean
monk seal, most species that are ecologically extinct probably
still survive in sufficient numbers for successful restoration
with proper management.
This optimism is in stark contrast to the situation in many
terrestrial ecosystems, where many or most large animals are
already extinct.
CORRECTING HISTORY
Rod Moore, executive director of the West Coast Seafood Processors
Association, questioned the interpretation of the new data by
some researchers, who blame marine fishing for many modern marine
problems. "Every naysayer and prophet of doom needs a scapegoat,"
Moore said. "The villain du jour seems to be 'overfishing' with
the American fisherman as the star evildoer." "There have to
be some questions raised before we all don our hard hats to
avoid the falling sky," added Moore. "But maybe this latest
study is right, so what we ought to do is stop fishing. Period.
And while we're at it, save the grasslands by stopping ranching,
and save the suckers and the natural flora by stopping farming.
I hear thatinsects are very nutritious. Ant souffle, anyone?"
But the scientists advocate major changes to management practices,
such as calling for massive restoration of the once vast oyster
reefs of Chesapeake Bay. This would result not only in cleaner
water but in an economic mainstay. Current plans for remediation
of eutrophication of estuaries are still based on the belief
that it is caused only by increased nutrients without regard
to overfishing of suspension feeders such as shellfish. "Clearly
we have allowed too much fertilizer to enter bay waters, but
we have also removed the major biological filters in the bay
to only one percent of historical levels in the Chesapeake Bay
and North Carolina's Pamlico Sound system," said Charles Peterson
of the University of North Carolina. "Oysters filter and clarify
bay waters. Oyster reefs provide habitat for blue crabs, rockfish
and many other valued fishery resources."
Other recommendations include the restoration of coral reefs
and seagrass beds by protection of fishes, sharks, turtles and
sirenians in very large reserves on the scale of all of Florida
Bay and the Florida Keys. The potential for reducing diseases
of corals and turtlegrass by restoring natural levels of grazing
is unproven but consistent with historical evidence. Historical
data not only help clarify underlying cause and rates of ecological
change, but they also demonstrate achievable goals for restoration,
management and exploitation of coastal ecosystems. "The many
tens of millions of sea turtles in the Caribbean before Columbus
easily exceeded the abundance and biomass of large animals in
East Africa," said Jackson. "All we do today is micromanage
remnants of once vast populations."
The scientists state that fisheries regulators and marine managers
need to move beyond their fixation on quotas and boundaries
and devise ways to restore the productivity and function of
coastal seas. "We need to change the way we think about our
coastal seas: not pristine, but damaged, and equally not hopeless,
but salvageable," explained Bradbury. "Our research points the
way.".
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