User:Earn A Pistach/Deraniyagala's beaked whale

Deraniyagala's beaked whale (Mesoplodon Hotaula) is a species of mesoplodont whale.

Taxonomy
''Mesoplodon. Hotaula'', commonly known as Deraniyagala's beaked whale, was initially known from seven stranded individuals. The first citing was recorded by Paules Edward Pieris Deraniyagala in 1963 and the newly discovered species was named after him. Two years later, controversy ensued over whether these stranded specimens were actually Ginkgo-toothed beaked whales.[2] The debate was resolved in the early 2000s after M. Ginkgodens and M. Hotaula were differentiated maternally by mitochondrial DNA, biparentally by autosomal, and paternally through Y chromosome inherited DNA sequences, as well as by morphological features. Their control region, cytochrome b, cytochrome oxidase, and various introns taken for genetic analysis demostrated thatgenetic variance (Dα) of the cytochrome b between Deraniyagala's whale and the Ginkgo-toothed beaked whale was 8.2% ± 1.79%, whereas genetic variance range between 5.5% to 16.6% in other Mesoplodon species (the smaller the percentage, the lesser the genetic differences between the two species).

Distribution
Deraniyagala's beaked whale is known from only seven individuals that have stranded themselves on beaches of various islands in the Indian and South Pacific Oceans: Seychelles, Maldives, Sri Lanka, Gilbert Islands, Kiribati and Line Islands. Observed distributions of Mesoplodon Hotaula strandings suggest that they prefer tropical habitats, as opposed to their closest known relative, the Ginko-Toothed Beaked Whale. It is thought that, like Cuvier's beaked whale, they live in insular populations.

A potential sighting occurred in the South China Sea in May 2019, although it was possible the sighted whales were ginkgo-toothed beaked whales.

Anatomy
Deraniyagala's Beaked Whales are on the smaller side for Mesplodonts. Although values for mean and maximum size are uncertain due to small sample size, from the 2019 sighting and stranded specimens, it appears that adult Deraniyagala's Beaked Whales are between 4-5 meters in length. It does not appear that adult males are larger than adult females. This is in line with other beaked whale species, which exhibit either reverse sexual dimorphism or sexual monomorphism

Like many other marine organisms, Deraniyagala's Beaked Whales exhibit countershading. Blue-black and brown black dorsal coloration have both been observed with, lighter shading on the underbelly. A pale, mottled cheek and white lower lip has been identified as a key indicator of the species. The eyes are situated about half a beak's length from the back end of the mouth, and a small, curved dorsal fin is situated two-thirds of the way along the body.

Other indicative anatomical features of Mesoplodon Hotaula include


 * Tooth alveoli are situated behind the point of fusion between the two halves of the mandible (mandibular symphysis).
 * A short mandibular symphysis.
 * The gingival margin of the pair of teeth is flat towards the front and becomes convex towards the back. Teeth are taller than they are wide and grow vertically.
 * The premaxillary bones are at least 60 mm wide at their greatest width and do not have a strong tilt (10-15 degrees).

Diet
Like other Mesoplodont whales, it is thought that Deraniyagala's whale feeds mainly on deep-sea squid-and-fish. Numerous cookie-cutter shark bite scars observed on stranded specimens and the 2019 life sighting attest to their deep-diving abilities.

Behavior
Beaked whales are suction feeders. They create a low-pressure environment in their oral cavity to suck prey towards their mouth. Due to this specialized feeding method, beaked whales have lost most of their teeth. After using suction to capture prey, they rely on simple sieving to keep the prey inside their mouth while expelling water.

Beaked whales like Deraniyagala's beaked whales have a complex foraging mechanism which involves the use of echolocation clicks to locate deep-water squid and fish during their foraging dives, and then use buzzes to capture their prey. There are different phases of acoustic behavior that beaked whales exhibit during foraging dives. The first phase is the search phase, where the whales emit regular clicks with varying echo returns as they pass through clouds of potential prey. The second phase is the approach phase, where the whale focuses on a specific target and continuously ensonifies it, receiving echoes until the transition to the final phase. The final phase is called the terminal phase, characterized by a rapid increase in click rate known as the buzz, followed by the interception of the prey through a sharp turn and increased acceleration.

The social structure of beaked whales is not well understood, but it appears that smaller species live in groups with a single mature male and females with their young, although larger groups have occasionally been observed as well. Older males with scars may be seen with different groups of females, indicating that they may fight for access to females using their teeth. In addition, stranded adult males of Deraniyagala's beaked whales have been found with chipped teeth that suggest combat with other adult males. A possible explanation for this may be that male beaked whales fight other males of the same species for control of a group of females.

Deraniyagala's beaked whales can also stay underwater for hours before surfacing to breathe. In 2019, a group of researchers observed beaked whales taking 3 short dives of between 14 and 18 minutes, briefly surfacing in between for 1-5 minutes. Then, after a fourth dive, the whales stayed submerged for 1.8 hours before resurfacing. This suggests that, like most other Mesplodonts, Deraniyagala's beaked whales are capable of staying submerged for hours at a time.

Conservation
Plastic pollution is a major issue threatening the lives of beaked whales. When plastics are ingested, they can cause blockages or tears in the digestive system, preventing the animal from properly digesting food and leading to malnutrition. Plastics can also release toxins into the animal's body, causing chemical poisoning. In addition to the direct physical impacts, ingestion of plastics can also negatively affect the behavior and reproductive success of marine animals.

Other ocean debris has been mentioned as a possible threat for Deraniyagala's beaked whales. The individuals suspected to be members of the species sighted in 2019 had unusual indentations on the lips, which researchers believed could have been caused by marine debris or fishing line. Additionally, a stranded individual was found on a beach in the Philippines in 2012, and died shortly after it was found. Further examination revealed that the whale had only a black rope and a piece of coal in its stomach. Researchers believed that the ingestion of these items could have led to the whale's death.