Environment
Historic Overfishing
Led to
Modern Ocean Problems
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.
A fish container
filled with the variety of fish
caught by a trawler during a normal
season
(Photo courtesy U.S. Coast Guard)
"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.
Fish waste is poured back into the sea
by a factory
trawler.
(Photo courtesy Greenpeace)
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."
Fish stored on ice in the hold of a
trawler
(Photo courtesy U.S. Coast Guard)
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. 
A white-tipped shark caught in a
fishers'
net (Photo courtesy Greenpeace)
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."
The Chesapeake Bay has lost
most of its sea grass beds
(Photo courtesy U.S. Fish and Wildlife Service)
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 turtle grass beds in Florida Bay can be attributed
to the ecological extinction of green sea turtles. Overkill of the green sea turtle
and other sea grass grazers such as dugongs and manatees has contributed to outbreaks
of disease and die offs in sea grasses.
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.
Fish nets used to come up full.
Now, too often, they are empty.
(Photo courtesy National Oceanic and
Atmospheric Administration)
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."
Fishing boats crowd a wharf at Cordova,
Southern Alaska (Photo courtesy
National Oceanic and Atmospheric Administration)
"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 that insects are very nutritious. Ant soufflé,
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 sea grass
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 turtle grass 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.
 Healthy
coral reefs provide shelter for many marine species,
including this
spotted scorpion fish camouflaged in the Flower
Garden Banks National
Marine Sanctuary, located off the
coasts of Texas and Louisiana (Photo
by Frank and Joyce Burek,
courtesy National Oceanic and Atmospheric
Administration)
"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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