Omura's whale off West Africa: autochthonous population or inter-oceanic vagrant in the Atlantic Ocean?

ABSTRACT

The surveillance of marine mammal strandings within the framework of a biomonitoring scheme for the Mauritanian coast led to the discovery in 2013 of a 3.98 m long, juvenile rorqual Balaenoptera sp. in an advanced state of decomposition near Chott Boul (16°32.488′N, 016°27.0317′W). Photographs and skin samples were taken, but the specimen could not be collected. Based on limited morphological evidence, only Balaenoptera edeni and B. omurai were plausible. Sequences of three mtDNA regions, i.e. parts of the cox1 and the cytb genes as well as the D-loop, for a total of 2636 bp (> 16% of the mitogenome) identified the specimen as an Omura's whale, B. omurai, the first record in the Atlantic Ocean and at least 11,400 km away from its closest known range in the SW Indian Ocean (Madagascar). The question of whether the specimen is a vagrant or belongs to an unrecognized Atlantic population is discussed. Advection by currents or transport on a ship's bow bulb following collision are discarded. Circumstances (juvenile status, great distance from Indo-Pacific, necessary inter-oceanic passage through cold temperate waters) may slightly favour the hypothesis that B. omurai, if rare, could be autochthonous in the Atlantic. Beach surveys remain a useful tool to assess trends in cetacean species composition, to detect unusual mortality events and to help assess the impacts of anthropogenic activities. This is particularly applicable to remote areas where the marine mammal fauna is poorly known and where fisheries effort is high, such as the Mauritanian coast.

KEYWORDS:

• Balaenoptera omurai
• biodiversity monitoring
• DNA barcoding
• Mauritanian coast
• Progamme ‘Biodiversité, Gaz, Pétrole’
• rorqual

Acknowledgements

We thank Jean-Philippe Gauthier-Placet-Nicolet for the preparation of Figure 1. WCM thanks Cherif Ahmed Ahmed Elmamy (ONISPA, Nouadhibou), Fatimatou Mint Yahya (ONISPA, Nouakchott), Oumar Ba (Nouakchott), Lematt Mint Hama (University of Tétouan, Morocco) Florence Dovillez and Younouss Kane (Programme BGP, Nouakchott) for their participation in the trimestrial monitoring missions. JLJ thanks Marie-Dominique Jezequel for technical assistance in the laboratory, Sami Hassani and the marine mammal team of Océanopolis (Brest) for numerous discussions about cetaceans. Special thanks go to Chantal Hily-Mazé. We thank the Mauritanian government, and particularly the Ministry of Environment (Ministère de L'Environnement et du Développement Durable), the Ministry of Oil (Ministère du Pétrole de l'Energie et des Mines) and the Ministry of Fisheries (Ministère des Pêches et de l'Economie Maritime) for their joint initiative to promote sustainable development in the frame of the innovative Programme ‘Biodiversité, Gaz, Pétrole’. Their efforts have been supported from the beginning by the German Cooperation GIZ (Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH), UNDP, IUCN and WWF, who also deserve our most sincere thanks. A special acknowledgement also goes to IMROP and ONISPA who, as national scientific institutions, are strongly committed to promoting biodiversity assessment and protection.

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

The field costs were supported by the Mauritanian government using funds from GIZ and UNDP through the Programme ‘Biodiversité, Gaz, Pétrole’ (BGP) (www.programmebgp.mr) (Project GIZ reference number 10.2044.5-005.00). Laboratory analyses were financed by the Université de Bretagne Occidentale (France) in the frame of ‘ERCS’ (Equipe reconnue par le Conseil Scientifique) programme for the BioGEMME laboratory.