Pilot whale
Pilot whales are cetaceans belonging to the genus Globicephala. The two extant species are the long-finned pilot whale and the short-finned pilot whale. The two are not readily distinguishable at sea, and analysis of the skulls is the best way to distinguish between the species. Between the two species, they range nearly worldwide, with long-finned pilot whales living in colder waters and short-finned pilot whales living in tropical and subtropical waters. Pilot whales are among the largest of the oceanic dolphins, exceeded in size only by the orca. They and other large members of the dolphin family are also known as blackfish.
Pilot whales feed primarily on squid, but will also hunt large demersal fish such as cod and turbot. They are highly social and may remain with their birth pod throughout their lifetime. Short-finned pilot whales are one of the few non-primate mammal species in which females go through menopause, and postreproductive females continue to contribute to their pod. Pilot whales are notorious for stranding themselves on beaches, but the reason behind this is not fully understood. Marine biologists have shed some light on the matter, suggesting that it is due to the mammals inner ear being damaged from noise pollution in the ocean, such as from cargo ships or military exercises. The conservation status of short-finned and long-finned pilot whales has been determined to be least concern.
Naming
The animals were named "pilot whales" because pods were believed to be "piloted" by a leader. They are also called "pothead whales" and "blackfish". The genus name is a combination of the Latin word globus and the Greek word Kephale.Taxonomy and evolution
Pilot whales are classified into two species; the long-finned pilot whale and the short-finned pilot whale. The short-finned pilot whale was described, from skeletal materials only, by John Edward Gray in 1846. He presumed from the skeleton that the whale had a large beak. The long-finned pilot whale was first classified by Thomas Stewart Traill in 1809 as Delphinus melas. Its scientific name was eventually changed to Globicephala melaena. Since 1986, the specific name of the long-finned pilot whale was changed to its original form melas. Other species classifications have been proposed but only two have been accepted. There exist geographic forms of short-finned pilot whales off the east coast of Japan, which comprise genetically isolated stocks.Fossils of an extinct relative, Globicephala baereckeii, have been found in Pleistocene deposits in Florida. Another Globicephala dolphin was discovered in Pliocene strata in Tuscany, Italy, and was named G. etruriae. Evolution of Tappanaga, the endemic, larger form of short-finned pilots found in northern Japan, with similar characteristics to the whales found along Vancouver Island and northern USA coasts, has indicated that the geniture of this form could be caused by the extinction of long-finned pilots in north Pacific in the 12th century, where Magondou, the smaller, southern type possibly filled the former niches of long-finned pilots, adapting and colonizing into colder waters.
Description
Pilot whales are mostly dark grey, brown, or black, but have some light areas such as a grey saddle patch behind the dorsal fin. Other light areas are an anchor-shaped patch under the chin, a faint blaze marking behind the eye, a large marking on the belly, and a genital patch. The dorsal fin is set forward on the back and sweeps backwards. A pilot whale is more robust than most dolphins and has a distinctive large, bulbous melon. Pilot whales' long, sickle-shaped flippers and tail stocks are flattened from side to side. Male long-finned pilot whales develop more circular melons than females, although this does not seem to be the case for short-finned pilot whales off the Pacific coast of Japan.Long-finned and short-finned pilot whales are so similar, it is difficult to tell the two species apart. They were traditionally differentiated by the length of the pectoral flippers relative to total body length and the number of teeth. The long-finned pilot whale was thought to have 9–12 teeth in each row and flippers one-fifth of total body length, compared to the short-finned pilot whale with its 7–9 teeth in each row and flippers one-sixth of total body length. Studies of whales in the Atlantic showed much overlap in these characteristics between the species, making them clines instead of distinctive features. Thus, biologists have since used skull differences to distinguish the two species.
The size and weight depend on the species, as long-finned pilot whales are generally larger than short-finned pilot whales. Their lifespans are about 45 years in males and 60 years in females for both species. Both species exhibit sexual dimorphism. Adult long-finned pilot whales reach a body length of approximately 6.5 m, with males being 1 m longer than females. Their body mass reaches up to 1,300 kg in females and up to 2,300 kg in males. For short-finned pilot whales, adult females reach a body length of about 5.5 m, while males reach 7.2 m and may weigh up to 3,200 kg.
Distribution and habitat
Pilot whales can be found in oceans nearly worldwide, but data about current population sizes is deficient. The long-finned pilot whale prefers slightly cooler waters than the short-finned and is divided into two populations. The smaller group is found in a circumpolar band in the Southern Ocean from about 20 to 65°S. It may be sighted off the coasts of Chile, Argentina, South Africa, Australia, and New Zealand. An estimated more than 200,000 individuals were in this population in 2006. The second, much larger, population inhabits the North Atlantic Ocean, in a band from South Carolina in the United States across to the Azores and Morocco at its southern edge and from Newfoundland to Greenland, Iceland, and northern Norway at its northern limit. This population was estimated at 778,000 individuals in 1989. It is also present in the western half of the Mediterranean Sea.The short-finned pilot whale is less populous. It is found in temperate and tropical waters of the Indian, Atlantic and Pacific Oceans. Its population overlaps slightly with the long-finned pilot whale in the temperate waters of the North Atlantic and Southern Oceans. About 150,000 individuals are found in the eastern tropical Pacific Ocean. More than 30,000 animals are estimated in the western Pacific, off the coast of Japan. Pilot whales are generally nomadic, but some populations stay year-round in places such as Hawaii and parts of California. They prefer the waters of the shelf break and slope. Once commonly seen off of Southern California, short-finned pilot whales disappeared from the area after a strong El Niño year in the early 1980s, according to the National Oceanic and Atmospheric Administration. In October 2014, crew and passengers on several boats spotted a pod of 50–200 off Dana Point, California.
Behavior and life history
Foraging and parasites
Although pilot whales are not known to have many predators, possible threats come from humans and killer whales.Both species eat primarily squid. The whales make seasonal inshore and offshore movements in response to the dispersal of their prey. Fish that are consumed include Atlantic cod, Greenland turbot, Atlantic mackerel, Atlantic herring, hake, and spiny dogfish in the northwest Atlantic. In the Faroe Islands, whales mostly eat squid, but will also eat fish species such as greater argentine and blue whiting. However, Faroe whales do not seem to feed on cod, herring, or mackerel, even when they are abundant.
Pilot whales generally take several breaths before diving for a few minutes. Feeding dives may last over ten minutes. They are capable of diving to depths of 600 meters, but most dives are to a depth of 30–60 m. Shallow dives tend to take place during the day, while deeper ones take place at night. When making deep dives, pilot whales often make fast sprints to catch fast-moving prey such as squid. Compared to sperm whales and beaked whales, foraging short-finned pilot whales are more energetic at the same depth. When they reach the end of their dives, pilot whales will sprint, possibly to catch prey, and then make a few buzzes. This is unusual, considering that deep-diving, breath-holding animals would be expected to swim slowly to conserve oxygen. The animal's high metabolism possibly allows it to sprint at deep depths, which would also give it shorter diving periods than some other marine mammals. This may also be the case for long-finned pilot whales. In 2024, a gps-fitted long-finned pilot whale recorded a diving depth over 1,100 meters.
Pilot whales are often infested with whale lice, cestodes, and nematodes. They also can be hosts to various pathogenic bacteria and viruses, such as Streptococcus, Pseudomonas, Escherichia, Staphylococcus, and influenza. One sample of Newfoundland pilot whales found that the most common illness was an upper respiratory tract infection.
Social structure
Both species live in groups of 10–30, but some groups may number 100 or more. Data suggest the social structures of pilot whale pods are similar to those of "resident" killer whales. The pods are highly stable and the members have close matrilineal relationships. Pod members are of various age and sex classes, although adult females tend to outnumber adult males. They have been observed making various kin-directed behaviors, such as providing food. Numerous pods will temporarily gather, perhaps to allow individuals from different pods to interact and mate, as well as provide protection.Both species are loosely polygynous. Data suggest both males and females remain in their mother's pod for life; despite this, inbreeding within a pod does not seem to occur. During aggregations, males will temporarily leave their pods to mate with females from other pods. Male reproductive dominance or competition for mates does not seem to exist. After mating, a male pilot whale usually spends only a few months with a female, and an individual may sire several offspring in the same pod. Males return to their own pods when the aggregations disband, and their presence may contribute to the survival of the other pod members. No evidence of "bachelor" groups has been found.
Image:1835 aquaimages.jpg|thumb|upright|Pilot whale mother and calf near Kona, Hawaii
Pilot whale pods off southern California have been observed in three different groups: traveling/hunting groups, feeding groups and loafing groups. In traveling/hunting groups, individuals position themselves in chorus lines stretching two miles long, with only a few whales underneath. Sexual and age-class segregation apparently occurs in these groups. In feeding groups, individuals are very loosely associated, but may move in the same direction. In loafing groups, whales number between 12 and 30 individuals resting. Mating and other behaviors may take place.