True's beaked whale (Mesoplodon mirus) in Macaronesia

The True's beaked whale (Mesoplodon mirus, True 1913) is a poorly known member of the Ziphiidae family. Its distribution in the northern hemisphere is thought to be restricted to the temperate or warm temperate waters of the North Atlantic, while a few stranding records from the southern hemisphere suggest a wider and antitropical distribution, extending to waters from the Atlantic coast of Brazil to South Africa, Mozambique, Australia and the Tasman Sea coast of New Zealand. This paper (i) reports the first molecular confirmation of the occurrence of the True's beaked whale at the southern limit of its distribution recorded in the northeast Atlantic: the Azores and Canary Islands (macaronesian ecoregion); (ii) describes a new colouration for this species using evidence from a whale with molecular species confirmation; and (iii) contributes to the sparse worldwide database of live sightings, including the first underwater video recording of this species and close images of a calf. Species identification was confirmed in two cases using mitochondrial DNA control region and cytochrome b gene markers: a subadult male True's beaked whale that stranded in El Hierro, Canary Islands, in November 2012, and a subadult male found floating dead near Faial, the Azores, in July 2004. The whale that stranded in the Canary Islands had a clearly delimited white area on its head, extending posteriorly from the tip of the beak to cover the blowhole dorsally and the gular grooves ventrally. This colouration contrasts with previous descriptions for the species and it may be rare, but it exemplifies the variability of the colouration of True's beaked whales in the North Atlantic, further confirmed here by live sightings data. The recording of several observations of this species in deep but relatively coastal waters off the Azores and the Canary Islands suggests that these archipelagos may be unique locations to study the behaviour of the enigmatic True's beaked whale.

Stranding data collection in the Canary Islands is performed by the Canary Islands Cetacean Stranding Network, funded by the Canary Islands Government and the Spanish Ministry MAPAMA. Long-term monitoring of beaked whales in El Hierro was funded by Fundación Biodiversidad-MAPAMA (2015) and ONR (2010–2014 and 2016). The Cetacean and Seabird Sighting Network of te Canary Islands (CETAVIST) was supported to University of La Laguna and GIC by Fundación Biodiversidad-MAPAMA within the project Canarias con la Mar. Strandings data collection in Azores was funded by FCT and FRCT, through TRACE-PTDC/MAR/74071/2006 and MAPCET-M2.1.2/F/012/2011 (FEDER, COMPETE, QREN European Social Fund, and Proconvergencia Açores/EU Program). MAS is supported by an FCT-Investigator contract (funded by POPH, QREN European Social Fund and the Portuguese Ministry for Science and Education). ELC was supported for the analysis by a Newton International Fellowship from the Royal Society of London and during writting by the EU-FP7 Marie Curie project “Behaviour-Connect”. NAS was funded during data collection of this work by the EU-FP7 Marie Curie project SOUNDMAR and during writting by project ECOSOUND within the Horizon 2020 EU Marie Slodowska Curie program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Peer reviewed