Vital marine species under threat

The Guardian (London) July 29, 2005,7369,1538548,00.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



"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."