True’s beaked whale, scientifically known as Mesoplodon mirus, is a rarely observed species of toothed whale belonging to the family Ziphiidae. This deep-diving marine mammal is one of the least understood whales in the ocean, with only a limited number of confirmed sightings since its discovery in 1913. It was named after Frederick W. True, a curator at the Smithsonian Institution, who first described the species from a stranded specimen in North Carolina.
Physical Characteristics and Identification
True’s beaked whales possess a small to medium-sized body, reaching lengths of 15.5 to 17.5 feet and weighing between 2,200 and over 3,000 pounds. Their body is robust, rounded in the middle, and tapers towards both ends. Females may be slightly larger than males.
Their coloration ranges from gray to brown on the dorsal side, with a paler ventral coloration. Northern Hemisphere individuals have a pale coloration across their melon and lack a dark, defined dorsal stripe, which helps distinguish them from similar species like Gervais’ beaked whales. Southern Hemisphere True’s beaked whales may display more white on their back, tailstock, and underside. They also feature dark patches around their eyes.
They have a moderately short, cone-shaped beak and a sloping forehead. A small, wide-based, and slightly hooked dorsal fin is positioned far down their back, typically two-thirds of the way along the body. Adult males exhibit a pair of teeth visible at the tip of their lower jaw, angled forward even when their jaws are closed. While females also possess these teeth, they are generally not visible, remaining below the gum line.
Habitat and Behavior
True’s beaked whales are found in temperate and tropical waters across the Atlantic Ocean, with known occurrences in the North Atlantic and at least two other regions in the Southern Hemisphere, including parts of the Indian Ocean. Their distribution is primarily known from strandings, with records off Nova Scotia, Canada, the Bay of Biscay, Ireland, Florida, and the Bahamas in the Atlantic, as well as off the coasts of Brazil, Madagascar, South Africa, New Zealand, and southern Australia. They prefer deep, offshore environments, diving to depths of 200 to 1,000 meters, and have been recorded as deep as 3,000 meters in pursuit of food.
These whales utilize suction feeding to consume small fish and cephalopods, such as squid. They employ echolocation to navigate and locate prey in the ocean depths. While their social structure is not fully understood, they are often observed alone or in small groups, averaging around five to six individuals.
True’s beaked whales have been known to breach and occasionally display other surface active behaviors. Their infrequent surface appearances and quick dives when disturbed contribute to the difficulty in observing them at sea. It remains unknown whether this species undertakes seasonal migrations or shifts in habitat use.
Conservation and Elusive Nature
The elusive nature of True’s beaked whale, stemming from its preference for deep, offshore habitats and deep-diving habits, makes direct observation and study challenging. Most information about this species comes from stranded individuals, making population assessment difficult.
The International Union for Conservation of Nature (IUCN) lists True’s beaked whale as “Least Concern,” but notes data deficiencies due to a lack of comprehensive information on their global population size and trends. The species is protected under various agreements, including the Marine Mammal Protection Act.
True’s beaked whales face threats primarily from human-caused ocean noise pollution, particularly from naval sonar and seismic surveys. These loud underwater sounds can disrupt their communication, navigation, and foraging behaviors.
While there is no current evidence of them being hunted, entanglement in fishing nets remains a general threat to cetaceans. Climate change also poses a potential risk by altering ocean temperatures and the distribution of their prey, possibly forcing these whales to expend more energy in search of food. Ongoing research and monitoring efforts, often utilizing passive acoustic methods, are important for expanding knowledge about this species and informing future conservation strategies.