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 user 2006-05-25 at 11:01:00 am Views: 112
  • #15543

    Fishing ‘major threat’ to turtles

    The endangered loggerhead turtle may face a greater threat than previously realised from longline fishing.

    Researchers found that many turtles spend considerably longer in the
    open ocean, where longline boats operate, than earlier studies had

    The boats aim to catch big predatory fish such as tuna
    and marlin, but accidentally snare other species including turtles and

    The new research is published in the journal Current Biology.

    Now you’ve got adults exposed to longline fisheries, which is very worrying

    Brendan Godley

    Until now scientists have believed that young turtles live in the open
    ocean, but change to a coastal habitat when they reach a certain size.

    But researchers working in Cape Verde found that most
    adults nesting there retain their open water behaviour, with the
    attendant risk posed by longline boats.

    “The bottom line is that we thought juveniles
    experienced this risk out in the open ocean with longline fisheries,”
    said Brendan Godley from the University of Exeter.

    “We thought that if you got them past that, then unless
    they’re being taken by inshore fisheries, you’re OK,” he told the BBC
    News website.

    “But now you’ve got adults exposed to longline fisheries, which is very worrying.”

    Twin lives

    Longline boats trail fishing lines tens of kilometres long, with baited
    hooks at regular intervals to catch some of the biggest and most
    powerful fish in the oceans.

    Sea birds and turtles are among the other creatures caught accidentally.

    With several thousand longline boats in operation, US scientist Larry
    Crowder has calculated that 1.8m hooks are set each night, and that a
    loggerhead turtle has about a 50% chance of encountering one each year.


    (Caretta caretta)

    are categorised as Endangered on the internationally-recognised Red List of Threatened Species.

    In theory, the turtles should be safe from longline vessels once they
    reach maturity, with research indicating that at an age of about 15 and
    a length of about 50cm they swap open water for a coastal environment.

    “[The young ones] venture out into the open ocean, and that’s thought
    to be because they hide in the open – the shore environment is the
    worst place to be for predatory fish,” said Dr Godley.

    “Then, we thought, they would grow to a size where if they
    come near to the shore they can deal with it, diving to 20 or 30 feet
    (six to 10 metres) [to hide from predators]. We always thought they
    moved into the inshore environment because the food supply is more

    Using satellite transmitters placed on the turtles to
    follow their movements – a technique pioneered by the conservation
    group, which co-funded the research – the team found that
    most of the adults did not make this switch.

    Most of the adult loggerheads swam in open water

    A minority journeyed to more fertile inshore feeding grounds

    Bigger individuals did, while smaller ones stayed away from the shore.

    This means, the researchers say, that attempts to conserve them will have to focus even more closely on longline boats.

    Bird conservation groups have developed a set of simple measures which
    they say can substantially reduce the annual bycatch of albatross,
    thought to number about 100,000.

    These include trailing streamers behind the boats to
    scare birds away, weighting hooks so they stay below the surface, and
    fishing at night.

    A similar set of measures to discourage loggerheads may
    not be so easy to develop, though keeping hooks deeper than the turtles
    usually dive may be one option, as may using blue-coloured bait, which
    they do not see as easily.