Abstract
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.
Highlights
Studies on animal distribution rely on the correct identification of the focal species during surveys
This paper reports the first occurrence of True’s beaked whales in the Canary Islands and the Azores confirmed with molecular markers
Genetic sex identification confirmed that both the whale that stranded on El Hierro (Canary Islands) and the whale found drifting in the Faial-Pico channel (Azores) were males
Summary
Studies on animal distribution rely on the correct identification of the focal species during surveys This can be challenging for marine mammals that are present at the sea surface for short time periods, when they share colouration patterns and morphology with closely related species. Ziphiids dive to depth for long periods of time, with only short breathing intervals at the sea surface (Tyack et al, 2006; Aguilar de Soto et al, 2012) They show large intraspecific variability in colouration and interspecific similarities in general morphology, including colouration patterns (Mead, 2009; Jefferson, Pitman & Webber, 2015). This results in a loss of precision in our knowledge about the distribution of individual species
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