Taxonomic confusion and market mislabelling of threatened skates: important consequences for their conservation status

1. The iconic European common skate (Dipturus batis) has been described as the first clear case of a fish species brought to the brink of extinction by commercial fishing. Its listing was upgraded to Critically Endangered on the 2006 IUCN Red List of Threatened Species. According to FAO fishery statistics, France is responsible for 60.2% of the 502 tonnes reported as D. batis in the 2005 world landings.

2. Noticeable phenotypic differences within the species and inconsistencies in published data on its sexual maturation required careful re-examination of its taxonomy. Morphology, genetics, and life history reveal that two distinct species have been erroneously confused since the 1920s under the single scientific name D. batis. Here it is argued that they should be resurrected as two valid species. The common skate D. batis species-complex is split into two nominal species, the blue skate (provisionally called D. cf. flossada) and the flapper skate (D. cf. intermedia) with maximum lengths of 143.2 cm and 228.8 cm respectively.

3. This taxonomic confusion puts into question all previously accumulated data based on D. batis. Its endangered status highlights the need for an extensive reassessment of population collapses with accurately identified species. In 2006/2007 an extensive survey (4110 skates, 14.081 tonnes by weight) was conducted in the main French ports of the D. batis species-complex and relatives (D. oxyrinchus, D. nidarosiensis and Rostroraja alba) that are mixed together in landings under the names D. batis and D. oxyrinchus.

4. The survey reveals that official fishery statistics mask species-specific declines, due to the mislabelling of five species under only two landing names. Trends in landings since the 1960s and the life history of these species suggest a dramatic decline and collapse of the spawning stock, preventing the recovery of relict populations.

5. The risk of extinction of these depleted species may be higher than previously assessed and might be unavoidable without immediate and incisive conservation action.