Species of mammal
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The short-finned pilot whale (Globicephala macrorhynchus) is one of the two species of cetaceans in the genus "Globicephala", which it shares with the long-finned pilot whale ("G. melas"). It is part of the oceanic dolphin family (Delphinidae).
It has a worldwide distribution with a global population of about 700,000, and there may be 3 or 4 distinct populations—two in the Pacific and one in the Atlantic and Indian Oceans. Its range is moving northward due to global warming. In the Pacific, males average and females . It generally has a stocky build with black to dark gray or brown skin, and can be distinguished from its counterpart by shorter flippers, fewer teeth, and a shorter beak. It is thought to pursue fast-moving squid typically at a depth of , but the maximum recorded depth is .
The short-finned pilot whale has been reported as being highly playful and social. It typically travels in pods of 10–30 members, usually family, but has been observed moving in groups of several hundred. Like killer whales, it has a matrilineal social hierarchy with an elder female at the head and a sizable post-reproductive lifespan. It is polygynous; females often outnumber males 8:1 in a pod.
Pods are known to mass strand, possibly due to sheer accident, biosonars confused by geomagnetic anomalies, injury from loud military sonar, or disease. It was historically whaled, and is still whaled today by Japan and the Lesser Antilles, but it is protected by several international treaties.
Taxonomy.
The name "pilot whale" originated with an early theory that pods were "piloted" by a leader. Other common names include the "pothead whale" (after the bulbous melon), and "blackfish" (a catch-all term used to designate numerous species of small, dark-colored toothed whales, including the pygmy sperm whale and false killer whale).
Worldwide, the diversity of mitochondrial DNA in short-finned pilot whales is considered to be low relative to other species with global distributions. A 2014 study found a unique haplotype in the Caribbean region.
Evolution.
The short-finned pilot whale is considered to be a single species with three divergent types: the Shiho, Naisa and Atlantic short-finned pilot whales.
The Shiho and Naisa forms are actually subspecies of the short-finned pilot whale, with the Shiho clade having diverged approximately 17.5 thousand years ago (kya), during the last glacial maximum. The exact boundaries of the two subspecies' ranges remain undefined due to lack of data. Based on current evidence, the Shiho subspecies is distributed in the eastern Pacific Ocean, and the Naisa subspecies encompasses the central/western Pacific and Indian Oceans, as well as the Atlantic Ocean. It appears as though the Pacific Ocean acts as a semi‐permeable barrier between the two subspecies, allowing occasional migration and mixing between the eastern and western Pacific Ocean, but keeping the populations separate enough to drive this differentiation.
The Atlantic clade is thought to have diverged from the Naisa approximately 12.5 kya, however this split is supported by mitochondrial DNA only, and not nuclear DNA. Further analysis is required to clarify whether the Atlantic Ocean and central/western Pacific and Indian Oceans pilot whales may also be sufficiently distinct to be considered subspecies.
The Atlantic and Indian/western-central Pacific types are also diverging from each other, with the Benguela Current off the coast of South Africa separating the two.
Description.
Short-finned pilot whales are black to dark gray/brown, with a thick tail stock, fluke with sharply pointed tips, bulbous head, and a broad, sickle-shaped dorsal fin. Coloration typically includes light grey to white areas such as a saddle patch behind the dorsal fin, a light grey or white anchor-shaped patch under the chin and belly, and a blaze marking behind the eye. These traits, however, can vary between populations. For example, two distinct forms are described from on the Pacific coast of central Japan: the Shiho morphotype is the larger of the two– females , males , and has a white dorsal patch and round melon, while the Naisa type is smaller– females , males – with a characteristic flattened or squarish melon and a darker, indistinct saddle patch. Short-finned pilot whales can reach up to in length and weigh up to , making it the third-largest species of oceanic dolphin, behind the orca and long-finned pilot whale. When they are born, short-finned pilot whales weigh about at a length of .
Long-finned and short-finned pilot whales are often hard to tell apart. However, as their names indicate, short-finned pilot whale flippers are shorter than those of the long-finned pilot whale, measuring about 1/6th of the body length. Short-finned pilot whales also have fewer teeth – 7–9 in each row – and a shorter and broader rostrum with a premaxilla that covers more of the maxilla. Both species exhibit sexual dimorphism and have similar lifespans of about 45 years for males and 60 years for females, with long-finned pilot whales being generally larger than short-finned pilot whales. The two species have limited overlap worldwide; long-finned pilot whales are found in cooler temperate waters, while the distribution of short-finned pilot whales is largely tropical and subtropical.
Geographic distribution.
Short-finned pilot whales are found in both coastal and pelagic waters in temperate and tropical regions of the Indian, Atlantic, and Pacific Oceans. Information on the spatial habitat use of pilot whales in the northwest Atlantic is limited, however short-finned pilot whales are thought to range from the southern end of Georges Bank into the tropics, overlapping with the range of the long-finned pilot whales along the mid-Atlantic shelf break between Delaware and Georges Bank.
Off the coast of Japan, the distributions of the Shiho and Naisa types are well-documented and largely nonoverlapping, with the Naisa-type inhabiting the warm-temperate waters of the Kuroshio Current, and the Shiho-type inhabiting cold-temperate waters of the Oyashio Current. Some evidence suggests these populations might even be distinct subspecies, based on differences in morphology, mitochondrial DNA and breeding seasons. Beyond Japan, the Naisa-type occurs in southeast Asia, the Indian Ocean, and Hawaii, and the Shiho-type can be found in the California Current and off Peru.
Pilot whales show strong natal philopatry, often remaining year-round in places such as Hawaii, the U.S. and British Virgin Islands, the Madeira Islands, and parts of California, though some populations migrate with the seasonal and annual fluctuations in temperature and productivity.
Once commonly seen off of Southern California, short-finned pilot whales disappeared from the area after a strong El Niño year in 1982 and 1983, and have since been encountered infrequently, primarily during warm-water years such as 1991, 1993, 1997, 2014, and 2015. It is not known whether the animals sighted more recently were part of the same population that was documented off Southern California before the mid-1980s, or a different wide-ranging pelagic population, therefore the status of this stock remains unknown.
Pilot whales are economically important in the whale-watching industry of some areas of the world, such as Madeira, Hawaii, and the Canary Islands, which host resident populations of these whales. The effects of tourism activities on pilot whales have not been well studied, but some evidence suggests that the impact of underwater noise from whale-watching boats can have the potential to significantly disrupt communication at close range. Many countries offer safe whale-watching guidelines designed to minimize the impact of their activities on the animals being watched (see supplementary materials).
Behaviour.
Social lives.
Short-finned pilot whales are long-lived, slow to reproduce, and highly social animals. They are usually found in pods of 10 to 30 individuals, though groups of up to several hundred short-finned pilot whales have been reported in the Caribbean. These pods are stable social structures, meaning that they form hierarchical associations that remain stable for generations, and are primarily thought to be matrilineal, i.e. led by an elder female relative, similar to those of resident killer whales. However, a study by Van Cise et al. (2017) showed that, in the Hawaii islands, the social organization of pods was indicative of familial behaviour rather than matrilineal, and was driven by genetic relatedness. Groups of closely related individuals formed tight associations, or clusters, with other close relatives, and genetic analysis revealed a significant differentiation between clusters, even those that were present in the same area. Clusters that were more genetically different also spent less time together. This could suggest that social behaviour in short-finned pilot whales inhibits gene flow outside of family groups.
Pilot whales are also known for their socializing and playful behaviour at the surface, such as lobtailing (slapping their flukes on the water surface) and spy-hopping (poking their heads above the surface). Members of a pod have also been observed making various altruistic behaviours, such as alloparental care, in which nonparent whales help to take care of young that are not their own. In the closely related long-finned pilot whales, babysitting of calves by other group members is frequently documented, and can be performed by males as well as females.
Reproduction.
Males are polygynous, meaning they will mate with multiple females at one time and throughout their lives. Pods are often found with around one mature male per every eight mature females. During mating aggregations, males will temporarily leave their pods to mate with females from other pods, but will return to their own pods once mating is over, which helps to prevent inbreeding. Female pilot whales mature at about 7–12 years of age, and will start having calves every five to eight years, averaging about 4 to 5 calves in a lifetime. A calf will suckle its mother for a minimum of two years, with most continuing to suckle for five years, and some evidence suggests that females may continue to lactate for up to 15 years after the birth of their last calf. A female will usually stop reproducing once reaching the age of 40 years, even though the maximum lifespan exceeds 60 years.
Foraging.
Short-finned pilot whales are apex predators. The diet preferences and foraging habits of short-finned pilot whales are still poorly understood, however, they are known to be deep-divers, and are generally found foraging on the steep slopes along the continental shelf break. The diet of these large marine predators is thought to consist primarily of squid, but will also include certain species of fish and octopus. On rare occasions, they are also known to prey on other marine mammals.
They use echolocation when they hunt, clicking and listening for echoes from prey as they descend and generating a rapid "buzz" of clicks at the depth of their dive that accompanies a high-speed sprinting attack.
They have been recorded to feed at a maximum depth of 1018 m (3340 ft) for a length of 21 minutes, although average dives tend to be shallower (around 700m) and last around 15 minutes. When foraging, a pod may spread out up to 800 m (half-mile) to find food. Pilot whales are known as the 'cheetahs of the deep' for the high-speed pursuits of squid at depths of hundreds of meters.
Population status.
The total of all available abundance estimates for short-finned pilot whales is approximately 700,000 individuals, but populations vary worldwide, and large parts of the species' range have not been surveyed, therefore actual abundance could be considerably greater than this.
In the western Pacific, population estimates range from 5,300 individuals in Northern Japan to 53,608 in Southern Japan. 7,700 individuals are reported in the eastern Sulu Sea (Philippines), and in the Eastern tropical Pacific the most recent estimate from 2000 gives 589,000 individuals. The resident population in Tenerife, Spain, is estimated at only 350 individuals.
Three stocks of short-finned pilot whales are recognized in U.S. waters, which live along the east and west coasts, and around the Hawaiian Islands. The best available abundance estimates place the West Coast stock at only 800 animals, and the East Coast stock at 21,500. These estimates come from sightings reported from vessel and aerial surveys, and may be under-representing the true population abundance due to the wide range that the species covers, and the difficulty of distinguishing long-finned and short-finned pilot whales at sea.
The Hawaiian archipelago is home to the Naisa-type short-finned pilot whale, which appears to be segregated into three island-associated communities based on photo-ID and satellite tagging data: the Main Hawaiian Islands (MHI) community, the Northwestern Hawaiian Islands (NWHI) community, found around O'ahu and Kaua'i Islands, and the central MHI community around O'ahu and Lāna'i Islands. There are no population estimates for the different island communities, but in all of Hawaiian waters there are an