Cover Story in Science Reveals

Historical Overkill of Marine Megafauna Triggered Current Ocean Crises


Sun, 29 Jul 2001


Leading Marine Scientists Call for Bold Measures to Restore Oceans

           While recent reports suggest Stone Age hunters drove dozens of species of
           huge land creatures to extinction, the cover story of the July 27 edition of
           Science describes the ecological extinctions of marine megafauna-vast
           populations of whales, manatees, dugongs, monk seals, sea turtles,
           swordfish, sharks, giant codfish and rays-from 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 management because historic data provide a framework for
           remediation and restoration that is otherwise invisible.

           "Comparing the magnitude of the mass ecological extinctions in the ocean to those
           on land may not be enough," states study co-author 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."

           "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,"
           says 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
           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," states Jackson.

           The data demonstrate that overfishing triggered changes in ecosystem structure and
           function as early as the late aboriginal and early colonial stages. Even more chilling,
           the scientists show that grinding down marine food webs is responsible for many of
           the problems we face 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.

           Water so clear you can see a cannon 30 feet down

           Examples of the negative chain reaction brought on by overfishing include:

Chesapeake Bay, the ocean birthplace of the U.S.A. is a bacterially
dominated, impoverished ecosystem. Historically oysters filtered the entire
water column every three days. Records describe a lost cannon, "clearly
visible in over 30 feet of water." Eutrophication commonly ascribed to
increased run-off and nutrient loading began instead with 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.

          Overfishing of large fish has led to overgrowth of algae on coral reefs, which
          has smothered the reefs and jeopardized the approximately 3 million species
          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. This has undermined the
          habitat's ability to serve as a food source, breeding and nursery ground,
          erosion protector and more.

          Many scientists have long suspected that overfishing has caused the
          well-publicized collapse of sea lion and sea otter populations in the Bering
          Sea. But new work related to this study by Alan Springer (University of
          Alaska) and co-author James Estes at UC Santa Cruz and several others,
          suggests that vast depletion of the great whales by humans has contributed to
          this collapse in a heretofore unrecognized manner. Whaling and overfishing
          forced killer whales to switch prey from the great whales to sea lions and
          most recently to sea otters - ultimately causing sea urchin barrens and the
          loss of kelp forests.

           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 nutrient loading, eutrophication, anoxia,
           disease, and climate change. Meanwhile various forms of human disturbance have
           increased and accelerated.

           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 with many terrestrial ecosystems where many or most
           large animals are already extinct.

          

           Correcting History - Integrated Ecosystem Management to Restore Oceans

           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 1 percent of historical levels in
           the Chesapeake Bay and North Carolina's Pamlico Sound system," states 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 that far exceed what we contemplate today.
           Scientific expectations for the recovery of marine ecosystems are too low because
           they are based on fisheries data that long postdate the decimation of fisheries.

           "The many tens of millions of seaturtles in the Caribbean before Columbus easily
           exceeded the abundance and biomass of large animals in East Africa," states
           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," states Bradbury. "Our research points the way."

          

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           Other authors of the study include: Wolfgang Berger, Michael Kirby and Carina
           Lange, Scripps Institution of Oceanography; Karen Bjorndal, University of Florida;
           Louis Botsford, University of California, Davis; Bruce Bourque, Bates College,
           Maine; Richard Cooke, Smithsonian Tropical Research Institute, Washington; Jon
           Erlandson, University of Oregon; Terrence Hughes, James Cook University,
           Townsville, Australia; Susan Kidwell, University of Chicago; Hunter Lenihan,
           Hatfield Marine Centre, Newport, Oregon; John Pandolfi, Smithsonian Institution,
           Washington, D.C.; Robert Steneck, Darling Marine Centre, University of Maine;
           and Robert Warner at University of California, Santa Barbara.

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           For more information please contact Dana Topousis at Fenton Communications:
           dtopousis@fenton.com  / 202-822-5200 ext. 238 or Jeremy Jackson at cell #
           858-518-7613. (Direct connect to France.) For a copy of the study please call
           202-326-6440 or contact scipak@aaas.org

Cover Story in Science Reveals Historical
Overkill of Marine Megafauna Triggered
Current Ocean Crises