What is a Cuvier's beaked whale?

Inconspicuous, elegant and the holder of extraordinary physiological records, the Cuvier’s beaked whale (Ziphius cavirostris), also known as the goose-beaked whale, is one of the most fascinating cetaceans in the world. Present in almost every ocean, it remains largely little known. For decades it was even thought to be extinct. Its scientific history, its physiological feats and its vulnerability to human activity make it a textbook case of modern marine biology.

A singular discovery

The story of Ziphius begins in 1823. The great French anatomist Georges Cuvier found a stranded skull at Fos-sur-Mer, on the French Mediterranean coast. Unable to match it to any known species, he described it scientifically in the belief that it belonged to an extinct species. The skull became the type specimen of a new species, named after him.

It took nearly 30 years, until 1850, for Paul Gervais to confirm that the species was in fact alive and widely distributed in the world’s oceans. It is one of the rare cases in the history of marine biology in which a species was described from a single fossil bone, then “brought back to life” by later sightings.

Its scientific name Ziphius cavirostris is itself telling. Ziphius is thought to derive from the Greek xiphos, “sword”, possibly in reference to the pointed teeth of the males. Cavirostris means “hollow beak”, in reference to the characteristic depression visible on the skull, a prenasal basin present in adult males whose exact function (probably linked to echolocation or to recognition between individuals) remains debated.

A plain, streamlined appearance

Physically, Ziphius is a medium-sized cetacean, between 5.5 and 7.5 metres long and 2 to 3 tonnes. Its body is slender, streamlined and hydrodynamic, typical of beaked whales. Its short conical rostrum, small lower jaw, small eyes and modest dorsal fin give it an unobtrusive profile. Its coloration ranges from chocolate brown to ash grey, often marked with linear scars caused by the teeth of rival males.

One remarkable anatomical detail: only adult males have functional teeth, in the form of two tusks visible at the front of the lower jaw. Females and juveniles have teeth buried in the gums, which never erupt. This feature suggests that the teeth serve less for hunting than for fights between males, in the manner of deer antlers.

The outright diving record holder

But it is in the depths that Ziphius shows what it can do. It is the outright record holder for diving among mammals. In 2014, a team of researchers using satellite tags documented a dive to 2,992 metres by a Cuvier’s beaked whale. In 2020, another study documented a breath-hold of 222 minutes, that is 3 hours and 42 minutes without breathing.

These performances far exceed those of sperm whales, which were long considered the best divers. They require a set of extreme physiological specialisations: ultra-concentrated muscle myoglobin, high respiratory capacity, deep bradycardia, a highly developed rete mirabile, and exceptional tolerance of CO₂ and lactate. It is one of the summits of marine mammal evolution.

A deep-sea diet

Ziphius hunts mainly deep-sea cephalopods, squid of various sizes and bathypelagic octopus, which it catches between 500 and 2,500 metres down. It rounds out its menu with a few deep-sea fish and crustaceans. This specialisation explains how rarely it is seen at the surface: it spends most of its time at depth, coming up only for brief breathing cycles.

It is therefore extremely difficult to observe at sea. Its blow is barely visible, its time at the surface is short (5 to 15 minutes between dives of 30 to 90 minutes), and its behaviour is generally unobtrusive. The biologists who study it often spend weeks at sea to gather no more than a handful of sightings.

A worldwide distribution

Ziphius is present in almost every ocean except polar waters. It is regularly recorded in the Mediterranean (in particular in the Ligurian Sea, the Alboran Sea and around the Balearic Islands), in the Bay of Biscay, around the Azores, Madeira and the Canary Islands, as well as in the Pacific, the tropical Atlantic and the Indian Ocean. Such ubiquity is exceptional for a deep-sea specialist cetacean.

An emblematic victim of military sonar

Unfortunately, it is also one of the cetaceans most affected by human activity, particularly mid-frequency military sonar. Its extreme diving physiology makes it exceptionally sensitive to acoustic disturbance. Several episodes of mass stranding have been correlated with naval exercises: the Bahamas in 2000 (17 Cuvier’s beaked whales), the Canary Islands in 2002 (14 individuals), the Alboran Sea in 2006.

The necropsies carried out by Antonio Fernández and his team revealed a decompression syndrome equivalent to the “bends” of human divers. A panicked flight to the surface compromises the normal gradual decompression, and nitrogen forms bubbles in the blood. Since those events, NATO navies have applied avoidance protocols in areas where Ziphius is present, and Spain has banned MFAS exercises around the Canary Islands outright. These are concrete steps forward for an extraordinary cetacean that would deserve a good deal more.

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