The strap-toothed beaked whale (Mesoplodon layardii), also known as Layard's beaked whale, is one of the largest members of the Mesoplodon genus, growing to in length and reaching up to .
The common and scientific name was given in honor of Edgar Leopold Layard, the curator of the South African Museum, who prepared drawings of a skull and sent them to the British taxonomist John Edward Gray, who described the species in 1865. This species is known for its unique coloration pattern and long, curved teeth that arch over the upper jaw, ultimately restructuring gape. This species inhabits deep subantarctic waters of the southern hemisphere. Strap-toothed whales rely on echolocation clicks, surface at step angles, and tend to travel in small groups. Their diet consists mainly of aquatic squid and males and females hunt the same sized prey. Although not a target for whaling, threats like plastic ingestion, noise pollution, and climate change can be threatening to Mesoplodon layardii.
Description
thumb|left|Skull of a male strap-toothed beaked whale
thumb|left|Small denticles on the upper surface of the male's tusks
Adult strap-toothed beaked whales show a distinctive colouration that perhaps makes them one of the most readily-distinguishable beaked whale species. Adults have a white beak, with a pale white 'cape' that extends to halfway between the dorsal fin and head. The dorsal fin is set far back down the body and is white-tipped. The flukes also have white tips. When observed closely, either at sea or when stranded, these whales show a pale neckband that separates the darker grey colouration found upon the head and melon from the rest of the body. While adult whales show striking colouration, juvenile animals are harder to distinguish from other beaked whale species, having a uniform grey colouration. Researchers have compiled a database of mitochondrial DNA sequences for all 21 recognized species of beaked whales. This allows for easier identification of whale species that may closely resemble each other the teeth may overlap at the tips, restricting the gape size of the animal. Two stranded adult male strap-toothed beaked whales were recorded as only being able to open their mouths 3.2 cm and 4 cm wide, compared to females and juveniles that had a gape size of 6.5 cm. It is thought male beaked whales use their teeth to compete for mating access to females, as evidenced by scars and scratches on the bodies of males. However it is unlikely the whale uses the whole tusk for such aggressive interactions, instead, it is probable that only a small denticle found upon the upper surface of the tooth is utilised. Late Pleistocene fossil remains attributed to this species have been reported from the Southern Ocean.
The northernmost extent of the range is continually changing; strandings were noted at 31–32° south of the equator along Brazil's southern coast until an emaciated carcass was found at 13° S on Maré Island off the north-east coast of Brazil in 2002. However, in 2011 an adult male strap-toothed beaked whale stranded alive in Myanmar at 16° north of the equator; more than 5000 km further north than the previously accepted range of the species. The whale died and a necropsy revealed that there was no prey within the stomach, but the overall body condition was good.
It is possible that this species migrates due to the seasonality of observed strandings. Research and sightings suggest that strap-toothed whales may approach coastal waters in the summer months to give birth. Coastal waters are inshore and shallower than preferred deep offshore habitats, which can allude to the few number of sightings with dive duration lasting between 10 and 15 minutes. The species can travel at speed, and may show 'porpoising' behavior. Although not known for their acrobatics, breeching has been seen among some individuals
Food and foraging
thumb|An adult observed in the Drake Passage.
The main prey of the strap-tooth beaked whale is thought to be oceanic squid species. One of these species being vampyroteuthis Infernalis, or the vampire squid, which is known to live 600 to 900 meters below sea level
Population status
The size of the population is unknown, however it has been noted that the species is one of the more common beaked whale species found in the southern ocean.
As the species has a largely circumpolar distribution, it is likely to be at risk from the impacts of anthropogenic climate change. Although the cause is unknown beaked whales being washed ashore or stuck in shallow waters are found to have developed gas pockets in the body causing tissue injury