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 user 2005-05-04 at 10:22:00 am Views: 106
  • #9233

    Tracking the Bluefin Tuna From Ocean to Sushi Platter

    For sushi aficionados, the essence of the Atlantic bluefin
    tuna is its fat-laced, butter-soft belly meat, called toro. For the long-liners,
    purse seiners, harpooners, trappers and fish farmers who seek the bluefin from
    Cape Hatteras to the frigid waters south of Iceland to the balmy Mediterranean,
    the fish are a potential bonanza, with choice specimens fetching $50,000 or more
    in Tokyo.

    But the intensifying trade in bluefin may soon empty the
    waters of this master of the sea.

    In just the last 35 years, exploding markets for
    sushi-grade tuna, combined with intensifying industrial-scale hunts aided by
    satellites and spotters in airplanes, have devastated not only the fish but also
    many fisheries.

    Dozens of Mediterranean towns that maintained coastal net
    traps for half a millennium or more are turning away from now-barren waters.
    Anglers off New England, who once watched great parading schools of bluefin
    migrate north at the end of each summer now scour the seas for scattered fish.
    Most vulnerable, by far, marine biologists say, is the apparently distinct
    population of bluefin tuna that breeds in the Gulf of Mexico.

    The threat to the bluefin was underscored last week by
    researchers who have tracked hundreds of the fish on their ocean-spanning
    journeys using electronic tags. They found that the tuna that spawn in the west,
    which are most severely depleted, are further threatened by an ever-broadening
    gantlet of hooks, seines, harpoons, traps and now farm-style pens, in which
    netted fish are raised and fattened – all to supply the Japanese sushi

    Dr. Barbara A. Block, a marine biologist at Stanford and
    the lead author of a study, published in the April 28 issue of Nature, said she
    found it hard to believe that “a fish of this size and beauty, an animal that
    had captured the hearts of fishermen and scientists alike for millennia, is
    slipping off Earth.”

    The bluefin, known to biologists as Thunnus thynnus, is a
    wonder of metabolic and evolutionary perfection, a Ferrari-like mix of
    refinement and brute power.

    Adult bluefins, some topping half a ton and living 40
    years, slice through icy or tropical waters while maintaining their body
    temperature around 80 degrees.

    Their physiology allows their ruby-red muscles to generate
    a split-second tail flick, rocketing the fish to on-ramp speeds in pursuit of
    prey. But having an oceanic range may also be their undoing, exposing them to
    harvests at every turn.

    Dr. Block has been studying the physiology and behavior of
    tunas for 25 years. Lately, she has spent much of her time at sea, surgically
    implanting tags in thrashing giants hauled briefly onto the decks of sport and
    commercial fishing boats assisting in her research.

    From her base next to the Monterey Bay Aquarium, which
    helps support her work, she leads a research team that focuses on every facet of
    the bluefin, from its evolution, genetics and unique muscle physiology to its
    diet and migrations.

    “We’re trying to see the planet through their lens,” Dr.
    Block said. But increasingly, she added, the bluefin are seeing the end of a
    fishing line, the inside of a net and the hold of a fishing boat.

    The new study is based on the research team’s grueling,
    decade-long effort to implant hundreds of increasingly sophisticated electronic
    tags in the giant fish, an enterprise that is beginning to reveal in new detail
    their ocean paths, from feeding grounds along the East Coast and in frigid
    waters south of Iceland to spawning areas in the balmy Gulf of Mexico and

    Most tagging studies provide only two data points – the
    place and time of release and the place and time of capture. In this study, 772
    fish were tagged with sophisticated devices that continually record body and
    water temperature, depth and daylight. Some tags stayed in the fish until they
    were caught, often for years. Others were intended to break a tether, pop to the
    surface and relay stored data to satellites after a programmed number of

    In all, 330 tags provided unparalleled records of fish as
    they repeatedly dove thousands of feet, traversed the ocean in a few weeks, and
    routinely crossed imaginary lines drawn nearly 25 years ago by tuna-fishing
    nations to divvy up what were thought to be separate eastern and western

    In the study, Dr. Block’s team showed that there indeed
    appear to be distinct populations of bluefin that spawn either in the gulf to
    the west or the Mediterranean to the east.

    But when the fish disperse across the Atlantic to feed,
    they mingle, rendering the management boundary, which runs along the 45th
    meridian, relatively meaningless.

    That means that big quotas, granted for two decades to
    countries fishing east of the line, probably added pressure to the ailing
    western bluefin population, said Dr. John J. Magnuson, an emeritus professor of
    zoology at the University of Wisconsin. He was chairman of a National Academy of
    Sciences panel that included Dr. Block and that assessed the tuna’s problems in

    “Fishing the mixed fishery as though it is a strong stock
    depletes and can eliminate the weak stock,” he said.

    The tuna spawning in the gulf are even more endangered, Dr.
    Block and her team said, because spawning “hot spots” overlap with areas where
    boats, using long lines of baited hooks, pursue another tuna species, the

    When big adult bluefin get caught on the lines, the
    researchers said, the warm water and their high-revving metabolism can push them
    beyond their physiological limits. Many die before they can be released. The
    toll is significant because it includes fish at the peak of their reproductive
    potential, the researchers said.

    In the paper, Dr. Block and her colleagues recommended
    seasonal bans on long-line fishing in spawning hot spots in the gulf. They also
    urged tighter controls on fishing in the Central Atlantic, where a feeding area
    straddles the existing boundary line and fish from both coasts congregate. Right
    now, that area is intensively fished by a host of countries with almost no

    Without action, Dr. Block said, the western population has
    little hope. “If such megafauna can disappear, imagine what else is occurring?”
    she said. “And it’s all because we do not have a system that manages the oceans

    American boat owners say that existing restrictions on
    long-line fishing in the Gulf are sufficient, and add that the spawning zones
    identified by Dr. Block are likely to shift each year, making specific
    “time-area closures” impossible. Long-liners in the area also use lightweight
    hooks that hold smaller yellowfin but are designed to uncoil under the powerful
    tug of a bluefin, they say.

    Dr. Block said that when she worked on long-line vessels in
    the region, the same smaller hooks caught and killed a substantial number of
    bluefin. She added that only a few percent of longliners in the area carry
    observers who independently tally bluefin deaths.

    Perhaps the biggest unresolved question is whether the new
    information can change an international regulatory regime that almost everyone,
    from anglers and commercial fishers to biologists and tuna diplomats, agrees is

    There are signs that the accumulated scientific evidence is
    starting to sway some members of the International Commission for the
    Conservation of Atlantic Tunas, the body created under a treaty in 1969 to
    oversee the fishery.

    For two decades, many marine biologists have criticized the
    organization for setting quotas too high and for favoring data and analyses
    provided by the industry.

    In an interview last week, Masanori Miyahara, the chairman
    of the commission and a senior fisheries official from Japan, acknowledged that
    the existing system had failed.

    “We’ve spent too much time under the wrong assumption –
    two-stock management,” he said. “After 25 years of those measures we don’t see
    any improvement in western spawners. We believe something is definitely

    He said that eastern catch limits needed to be better
    enforced, and he noted that a particular problem was the greatly increased
    penning of Mediterranean tuna, which disrupts spawning.

    A meeting of scientific advisers to the commission will
    take place next month to consider new ways to manage the fish stocks. Mr.
    Miyahara added that Japan was particularly committed to restoring the

    “We feel some responsibility for this mess,” he said.
    “Japanese buyers are running all around the world and buying as many fish as
    possible, particularly bluefin.

    “We’re seriously working with our buyers now to contain
    their eagerness,” Mr. Miyahara said.

    Even with such statements, and the new research, many
    scientists and scholars who study tuna and tuna fishing said they doubted much
    would change.

    Glenn Delaney, an American who formerly served on the
    international commission and represents American fishing companies at meetings
    of the group, said Dr. Block’s findings, while possibly correct, were at best
    preliminary and spotty – and thus unlikely to move the commission to act.

    Mr. Delaney is one of many people in the tuna debate,
    including a host of biologists and environmental campaigners, who view Europe as
    a bigger impediment to better protections than Japan or the United States. Under
    the longstanding division of the Atlantic bluefin population, Europe has long
    had the advantage, with recent quotas of more than 30,000 metric tons of bluefin
    a year; less than a tenth that is allocated for western waters.

    In an e-mail message, John Spencer, the chief European
    negotiator in international commission meetings, said that Europe had an “open
    mind” about management options after 2006. But, he added, “If we are going to
    change the current system, which has brought stability to the management, then
    we need to be demonstrated the added value of any new system.”

    William T. Hogarth, the assistant administrator for
    fisheries of the National Oceanic and Atmospheric Administration, said that
    trade sanctions or other economic measures may be required to push some
    countries to end routine violations of size and catch limits by their

    As long as the issue is hashed out only in the invisible
    realm of fisheries bureaucracies, there will be little progress, environmental
    experts and industry representative agreed.

    They also agreed that while the international commission
    has been a problem, the organization and the underlying treaty are the only
    source of a solution, as well.

    For the moment, however, there are few signs of change.
    Last month, a group of fisheries experts from the international commission met
    in Fukuoka, Japan, to ponder alternative systems for managing the shared
    resource. The main camps – the United States, Europe and Japan – staked out
    starkly different positions.

    Several tuna experts who were not involved with the new
    study said that Dr. Block’s pointillist maps, showing the movements of some tuna
    for more than four years, were sufficiently concrete that they could force an
    end to the prolonged stalemate.

    “Without her, we’d be in exactly the same place we were 15
    years ago: a bunch of theoreticians waving their hands and a bunch of European
    fisheries politicians arguing the case based on no data,” said Dr. E. Don
    Stevens, an emeritus professor of zoology at the University of Guelph in Ontario
    and an author of the 1994 National Academy of Sciences tuna study.

    “If the managers do not accept this evidence,” Dr. Stevens
    said, “then it seems to me that they will never accept any evidence and that
    their argument is not based on logic but rather is based on shortsighted
    political grounds.”