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Is 80-year-old mistake leading to first species to be fished to extinction?

19.11.2009
Species of common skate driven into 'irreversible decline'

A species of common skate is to become the first marine fish species to be driven to extinction by commercial fishing, due to an error of species classification 80 years ago, reveals research published today in the journal Aquatic Conservation.

The European common skate, Dipturus batis, has been on the World Conservation Union's Red List of Threatened Species since 2006, with France currently being responsible for 60.2% of reported landings. These catches are predominantly registered under the name 'D.batis,' however researchers, led by Dr Samuel Iglésias, show that 'D. batis' is in fact two clearly distinct species which have been incorrectly categorised as one since the 1920s.

From the mid-19th century the common skate was described as two distinct species, the flapper skate, D. intermedia, and the blue skate, D. flossada. However, in an influential work in 1926 R.S Clark recognised only 'D. batis' as a valid species and this classification has largely gone unchallenged since.

This classification confusion has resulted in the depletion of the flapper skate, the more endangered species of the two, being masked in the catch record. This means the risk of extinction is far higher than previously assessed and without immediate and incisive action the species may be in an irreversible decline towards extinction.

When conducting sampling in fish markets during the start of this study Dr Iglésias observed noticeable morphological differences in the 'Dipturus batis' specimens he sampled. In order to understand these differences the researchers not only analysed the systematic molecular data but also reviewed the species' life history and analysed fishery statistics.

"As the species was listed as 'Critically endangered' I wanted to understand who's who? I estimated at the beginning that it would take some weeks to resolve this question, but in the end it took me about two years," said Iglésias. "Our research clearly shows that D. cf. flossada and D. cf. intermedia are distinct and should be resurrected as two valid species."

Common Skates, which were once abundant in British and European waters, have been in sharp decline for decades. In 2008 the International Council for the Exploration of the Sea (ICES) noted that the species is depleted in the Celtic and North Seas, the Skagerrak and the English Channel. The ICES advised no target fishing and that by-catch should be minimised.

"The threat of extinction for European Dipturus together with mislabelling in fishery statistics highlight the need for a huge reassessment of population for the different Dipturus species in European waters," concluded Iglésias. "Without revision and recognition of its distinct status the world's largest skate, D. cf. intermedia, could soon be rendered extinct."

Ben Norman | EurekAlert!
Further information:
http://www.wiley.com

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