"Small delphinids" identification: from scientific confusion to conservation issues

Résumé En

Taxonomic confusion can lead to misestimation of population and to lack of accurate data guaranteeing a reliable conservation status assessment. Small delphinids have been confused since ancient times, and unfortunately it is still the case for other reasons. Ancient scientists as Aristoteles only distinguished ‘dolphins’ from fishes or from whales. Renaissance scholars already stated differences between several vernacular names for the presumed same animals, whereas several similar species could be confused under the same name, as ‘dolphin’ and ‘porpoise’. For example, the striped dolphin (Stenella coeruleoalba) presumably inhabits the Mediterranean Sea since centuries without being specifically described, as a proper name (and precise associated identification criteria) was missing until the middle of the 19th century (before Gray and Gervais). This situation led to misidentifications and confusion with the so called “common dolphin”, Delphinus delphis, considered as the only common dolphin in the area or used as a generic name. Finally, the name “delphinus coeruleoalbus” was retroactively given after Meyen, who described and sketched this animal off Brazil (1833), during a German expedition on the Prinzess Louise. Consequently, the striped dolphin Mediterranean presence was certainly underestimated. But, whereas the difference seems now clearly established, the status of the common dolphin remains uncertain in the Mediterranean Sea: geographical repartition, abundance trends remain in question. This taxonomic confusion is still observed and can lead to an incorrect assessment of present species conservation status. Moreover, the latest method for abundance estimation, by aerial survey, is likely to reduce knowledge instead of increasing, because both dolphins are often processed under one single appellation, “small delphinids”. In case of fisheries bycatch issues, such as in the Bay of Biscay, the conservation status of each species is regrettably again unsure, because ‘safe’ bycatch thresholds are expressed as a fraction of population estimates (for example 1%).