Strap-toothed whale

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Strap-toothed beaked whale, Mesoplodon layardii, also known as Layard's beaked whale, is one of the largest species in its genus. Adults reach about 6.2 meters (20 feet) long and weigh roughly 1,000–1,300 kilograms. Newborn calves can be up to 2.8 meters long.

Appearance: Adults have a distinctive white beak and a pale white cape that extends halfway between the head and dorsal fin. The dorsal fin sits far back on the body and is white-tipped, and the flukes have white tips. A pale neck band separates the darker head and melon from the rest of the body. Juveniles are more uniformly gray.

Teeth and sex: Only males have usable teeth. Males grow a large flat tusk from the lower jaw that curves back toward the head, up to about 34 cm long. The teeth can overlap at the tips and limit how wide the mouth can open. In some stranded adults, males could only open their mouths about 3–4 cm, while females and juveniles could open about 6.5 cm. The teeth likely help males compete for mates, but only a small denticle on the tooth is used in fighting.

Range and habitat: They live across the Southern Ocean and nearby temperate waters, possibly in a circumpolar distribution. Records exist from Argentina, the Falkland Islands, Australia, New Zealand, and more. A live stranding in Myanmar in 2011 showed the range can extend far north. The species may migrate with the seasons.

Behavior: They usually travel in small groups of 2–10. They are hard to study at sea and often do not show their flukes when diving. Dives typically last 10–15 minutes. They may travel fast and show porpoising at the surface.

Predators and diet: Killer whales have been observed chasing and killing strap-toothed beaked whales. Their main prey is oceanic squid; stomach analyses show most prey are cephalopods, with some fish and crustaceans. Both males and females hunt similar-sized squid, though males’ shorter mouth opening may influence feeding.

Conservation: The IUCN lists this species as Least Concern. They are not hunted commercially but face threats from entanglement, disturbance from human noise such as sonar, and potential impacts from climate change. The population size is not known, but they are among the more common beaked whales in the southern oceans.