MAJOR THREAT FROM LONGLINE FISHING
MAJOR THREAT FROM LONGLINE FISHING
2006-05-25 at 11:01:00 am #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
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
“But now you’ve got adults exposed to longline fisheries, which is very worrying.”
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.
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 seaturtle.org, 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.