True’s whales breaching, showing different colouration. Dylan Walker

A comprehensive review of material gathered by scientists, tourism operators and sightseers has thrown a little extra light onto the True’s beaked whale, one of the least understood species in the world.

The mysterious mammal (Mesoplodon mirus) is very rarely seen, but no one knows whether that indicates it is endangered, or simply difficult to find.

There are 22 species of beaked whale, all belonging to the family Ziphiidae, three of which were discovered just in the past two decades. All are deep diving, deep ocean residents, making identification and study extremely challenging.

The True’s beaked whale has been recorded in the North Atlantic and the waters off Australia, but nowhere in between. Whether this represents a gap in distribution or simply the absence of sightings is unknown.

So elusive is the species that there have until now only been three live sightings in the North Atlantic – and at least one of those is uncertain, and might have been the similarly coloured Gervais’ beaked whale.

Now, however, a team of scientists led by Natacha Aguilar de Soto from the University of St Andrews in Scotland has collated a treasure trove of True’s beaked whale data from sources including other researchers, whale watch crews and tourist guides, all based around the Azores and Canary Islands.

A True’s whale family group, comprising two adults and a calf. Roland Elder

The islands are thought to comprise the southernmost limit of the whales’ northern hemisphere range, but may also be a hotspot for feeding, mating and calving. The data collected includes photographs, unique video of the whales underwater, and even genetic details from several beached dead animals.

The results, published in the journal PeerJ, provide fascinating clues about the species, but also raise more questions than they answer. de Soto’s team, for instance, discovered that True’s beaked whales vary widely in colour, potentially confounding live identification. The team hopes to use the genetic data to study gene flow through the species in the northern hemisphere and then, ultimately, compare the results to the so far scant data available for southern hemisphere.