The Guardian (London) July
29, 2005
http://www.guardian.co.uk/fish/story/0,7369,1538548,00.html
By Tim Radford, science
editor
The great predators of the
seas - tuna, swordfish, marlin and others
- could be on the way out.
Canadian researchers who surveyed the
catches from ocean fishery
"hotspots" warn that not only are numbers
in decline, but also the
variety of species in any region.
The research, published in
Science today provides fresh ammunition
for conservationists who want
to see the creation of large,
internationally protected
marine parks where fish populations can
breed and recover.
Boris Worm and Ransom Myers
of Dalhousie University, who showed in
2003 that shark populations
in the north Atlantic had fallen by 90%
in 15 years, combed fisheries
data for the past 50 years to discover
that catches were becoming
less diverse.
Where fishermen might once
have caught 10 different species, they now
haul in only five. "It's not
yet extinction - it's local fishing out
of species," Dr Myers said.
"Where you once had a range of species in
dense numbers, now you might
catch one or two of a certain species."
Oceans cover 70% of the
planet: they are also exploration's last
frontier. The research
highlights a pattern of hotspots in the open
ocean where tuna, swordfish
and other predators congregate,
presumably to hunt smaller
fish attracted by local surges of
zooplankton in the high
seas.
For the first time, marine
scientists have begun to understand why
sea surface temperatures and
other conditions make some fishing
grounds richer than
others.
But for some species of
commercial fish, it may already be too late.
Cod catches are in sharp
decline, the Atlantic halibut has all but
disappeared, and bluefin tuna
catches are now controlled.
"This is the great joy of
science," Dr Worm said. "It is like solving
a giant puzzle and seeing the
night sky in constellations for the
first time, even as the stars
are blinking out. Beautiful and tragic
at the same time."
The two started with catches
logged by Japanese long liners. Pelagic
long liners pay out baited
hooks on lines up to 60 miles long. Though
the fishermen may be after
bluefin tuna, or swordfish, they also
catch other kinds of tuna and
billfish as well as sharks, sea turtles
and even
albatrosses.
They matched this evidence
against data collected independently by
Australian and US
researchers, who counted more than 140 species in
the same regions in the past
15 years. They concluded that the
diversity of big predators
had fallen by up to 50% in the last five
decades.
"In every ocean basin, our
hotspots today are only relics of what was
once there," Dr Worm
said.
"While some hotspots have
already disappeared, there are still some
very special places where
species concentrate. We have the chance and
the political measures to
protect some of these areas."
He added: "To me, it's the
most important thing in the world: to keep
as many pieces of the puzzle
as we can before we destroy it."
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