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Last Updated: Thursday, 22 February 2007, 14:11 GMT
Threat to ocean sharks increases

Blue shark. Image: J.Stafford-Deitsch/Shark Trust
The blue shark is declining but not yet considered threatened
The threat to ocean-going sharks is more severe than previously thought, according to conservation experts.

Scientists with the World Conservation Union, which publishes the Red Lists of Threatened Species, have upgraded the "threat" category of several sharks.

Those now considered "vulnerable to extinction" include the shortfin mako, a favourite of recreational fishermen, and the long-tailed thresher shark.

Scientists say over-fishing is a principal reason for the decline.

The World Conservation Union's (IUCN) shark specialist group announced its re-assessments at a workshop in Oxford, UK.

Several species are now threatened with extinction on a global scale
Sarah Fowler
"Despite mounting threats and evidence of decline, there are no international catch limits for pelagic (ocean-going) sharks," said Sonja Fordham, deputy chair of the shark specialist group and policy director for the Shark Alliance.

"The workshop results underscore the urgent need for international fishery commissions to limit fishing for these vulnerable species and strengthen regulations on the wasteful practice of finning."

Cutting off shark fins, which are prized for soup in some east Asian cultures, is banned in many fisheries. But IUCN says enforcement is often weak.

Mature problem

Sharks are more vulnerable than many other types of fish to environmental threats because they generally mature slowly and reproduce relatively late in life.

Whale shark, Image: Rachel T Graham

"The qualities of pelagic sharks - fast, powerful, wide-ranging - too often lead to a misperception that they are resilient to fishing pressure," commented Sarah Fowler, shark specialist group co-chair.

"But several species are now threatened with extinction on a global scale."

The world's biggest fish, the whale shark, is one of them. Researchers found evidence last year that so many large specimens are being caught that the average length of the fish is falling.

However, many of the most threatened species are found in rivers and coastal waters, with the Ganges shark, the striped dogfish of South America and the European angel shark among those considered "critically endangered".

The new assessment sees the status of the scalloped hammerhead, another coastal species, worsen from "near threatened" to "endangered".

Hammerheads are among the most commonly caught sharks for finning.

RED LIST DEFINITIONS
Extinct - Surveys suggest last known individual has died
Critically Endangered - Extreme high risk of extinction
Endangered - Species at very high risk of extinction
Vulnerable - Species at high risk of extinction
Near Threatened - May soon move into above categories
Least Concern - Species is widespread and abundant
Data Deficient - not enough data to assess
Accidental catching by fishermen is as much a threat as targeted fishing.

There is a complex set of criteria for deciding which species go in which category of risk.

"Vulnerable" can mean that species numbers have declined by 50% in 10 years if the main threat is removed, or by 30% if the threat is still present; "critically endangered" can mean a 90% decline over 10 years.

The Oxford workshop is one of a series in which IUCN scientists are aiming to generate a more accurate picture of the threats to sharks and their close cousins, the rays.

Many of these species have not been studied sufficiently for scientists to assess their status, yet threats in the form of fishing and habitat disruption are clearly present.




SEE ALSO
Sharks 'should be shown compassion'
26 Jan 07 |  Science/Nature
Shark-finning measures 'too weak'
31 Aug 06 |  Science/Nature
Protection for threatened sharks
08 Jul 06 |  England
More species slide to extinction
01 May 06 |  Science/Nature
Study warns of threat to sharks
22 Feb 06 |  Scotland
World's biggest fish 'shrinking'
17 Jan 06 |  Science/Nature

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