Gray, 1846. The derivation of the name is from the Latin globus, for "globe or ball", the Greek kephale for "head" and from the Greek macro meaning "enlarged" and rhynchus meaning "snout, beak". The common name "pilot whale" refers to the belief that there is a leader, or "pilot" of the pod that leads the group and that the group will follow this leader, even when it means certain death. Fishermen and whalers referred to pilot whales as "potheads" because of their bulbous heads, and as "blackfish." The latter term, however, is also used for killer, false killer, pygmy killer and melon-headed whales.
The oldest fossil of a pilot whale was found in Pliocene or Pleistocene deposits in England, and several younger fossils have been found in North America, in Florida and California.
Size, shape and distinctive characteristics
Short-finned pilot whales are among the largest of the delphinids with males reaching 6 to 7m and females reaching 5.5m. Males may weigh nearly 3,600 kg. Pilot whales have long robust bodies and bulbous heads, with upsloping mouthlines, and extremely short or non-existent beaks. The dorsal fin, which is situated about 1/3 of the way back from the head, is low and falcate, with a wide base relative to its height (varying with age and sex). The pectoral fins are long and sickle-shaped, up to 1/6 of the body length. There are seven to nine pairs of short pointed teeth in both the upper and lower jaws.
Pilot whales are dark gray to black, with a white to light gray anchor-shaped patch on the chest, a light gray saddle-patch behind the dorsal fin, and a light gray or white streak from behind each eye that extends to the front of the dorsal fin.
In the areas of overlap, the short-finned pilot whale is difficult to distinguish from the long-finned pilot whale (Globicephala melas). Morphological differences between the two species include pectoral fin length, and differences in skull shape and number of teeth, but these differences are subtle and the two species cannot be reliably distinguished at sea. Most sightings can be tentatively assigned to species based on the geographic location. Other species, such as false killer whales, and less commonly, pygmy killer and melon-headed whales, may be confused with pilot whales at a distance; however, the head shape and dorsal fin shape and position are different.
The short-finned pilot whale is found in most of the tropical, subtropical and warmer temperate areas of the world's oceans, with the exception of the Mediterranean Sea. In the western North Atlantic, the short-finned pilot whale ranges from the mid-coast of the United States southward into the Caribbean and the Gulf of Mexico. In the eastern North Atlantic, short-finned pilot whales range from the coast of France in the north to Madeira and the coast of Northwestern Africa.
In the western North Pacific, two distinct populations of short-finned pilot whales are found off northern and southern Japan. These populations differ markedly in coloration, size, body shape, and cranial features and are geographically and genetically separated (Rice 1998). This has resulted in debate regarding their taxonomic status, although currently they are both classified as Globicephala macrorhynchus. In the eastern North Pacific, the short-finned pilot whale is commonly found from the coast of central California to Hawaiian waters and the eastern tropical Pacific. On rare occasions, the short-finned pilot whale may be seen in waters as far north as Vancouver Island and Alaska. Latitude 25°S is the southernmost occurrence for both the Atlantic and Pacific coasts of South America.
Distribution of the short-finned pilot whale in the southern hemisphere is not as well known, but they have been found in Sao Paulo, Cape Province, Western Australia, Tasmania, New Zealand, and the Indian Ocean.
Ecology and Behaviour
Short-finned pilot whales are typically found in deep waters on the continental shelf and shelf break, and the continental slope and in areas of high topographic relief. Seasonal inshore/offshore movements of pilot whales are thought to be related to the distribution of squid, their primary prey. A recent study by Aguilar Soto et al. (2008) demonstrated that short-finned pilot whales off the Canary Islands make foraging dives to depths of up to 1019m and 21 minutes in duration and engage in vertical sprints of 9m/s in order to capture fast moving prey.
Pilot whales are highly social; they are most often found in pods of 20-100 individuals, but some groups may number over 1000. From photo-identification and genetic studies, researchers believe pilot whales live in stable family groups, similar to those of killer whales, and not in the more fluid groups characteristic of many smaller dolphin species. These stable family groups consist of related females and their offspring. Mature males also occur in these groups, but genetic evidence has shown that these males are not the fathers of the calves in the group. Several calves in one group may be fathered by the same male, suggesting that a male can enter a group for a brief period and mate with more than one female. Pilot whales appear to remain in their natal group for life; this type of social structure is very unusual among mammals. Consistent with their sexual dimorphism and adult sex ratio, pilot whales are polygynous.
Short-finned pilot whales are among the species of cetaceans that most frequently mass-strand, perhaps due to their strong social bonds (Hohn et al. 2006).
There is pronounced sexual dimorphism in short-finned pilot whales with males being longer and heavier, having a more pronounced melon and a much larger dorsal fin than females. Female short-finned pilot whales reach sexual maturity at six to seven years of age, while males do not reach sexual maturity until they are 12 or more years old. Gestation lasts 12 to 15 months and lactation continues for at least two years. The calving interval averages from five to eight years and females continue to ovulate until almost 40 years old. Calving peaks occur in spring and fall in the southern hemisphere, and in fall and winter in the northern hemisphere. Females cease ovulating at around 40 years but may live another 20 years in a post-reproductive state. They may continue to nurse their last calf for up to 15 additional years after they cease breeding. Kasuya and Marsh (1984) found that the duration of lactation increased with increasing age and concluded that older females invest less in calf bearing and more in calf rearing.
Squid are the preferred prey of short-finned pilot whales, but they also consume fish. They feed via suction. In the Atlantic, Mintzer et al. (2008) determined that the oceanic squid Brachioteuthis riisei was the most important prey, although the squid species Taonius pavo and Histioteuthis reversa were also a substantial component of the diet. In addition, the whales fed on the fish Scopelogadus beanie, a deep-diving oceanic species. Short-finned pilot whales along the U.S. Pacific coast primarily eat the neritic cephalopod Loligo sp. (Seagars and Henderson 1985, Sinclair 1992). Kubodera and Miyazaki (1993) identified ommastrephids and octopods as common prey off Japan.
Estimates of abundance exist for several areas. The northern form off Japan has a subpopulation estimated at 4,000-5,000, and the southern form has an estimated subpopulation of about 14,000 in coastal waters (Miyashita 1993). There are an estimated 589,000 short-finned pilot whales in the eastern tropical Pacific (Gerrodette and Forcada 2002), and an estimated 304 in waters off the North American west coast (Barlow 2003). In Hawaiian waters, there are estimated to be 8,846 (Barlow 2006). The Gulf of Mexico contains at least 2,388 animals (Mullin and Fulling 2004). In the Exclusive Economic Zone of the eastern U.S. there are an estimated 31,000 pilot whales, but this estimate includes both long- and short-finned pilot whales (Waring et al. 2009).
The IUCN Red List of Threatened Species lists the short-finned pilot whale as "data deficient". Currently, the short-finned pilot whale is treated as one species even though there is evidence that it may be a complex of two or more species. If the taxonomic designations change, it is possible that new species could be listed under higher categories of risk. This species is listed on CITES Appendix II.
Harvest: Humans have long taken advantage of the highly social nature of pilot whales by hunting them in "drive fisheries," in which pods of whales are herded into shallow water and driven to the beach where they are slaughtered. Short-finned pilot whales in the western Pacific have been hunted for centuries in both drive and harpoon-gun whaling operations. Meat, blubber and oil are produced from these activities. From 1985 to 1989, Japan took a total of 2,326 short-finned pilot whales (Bernard and Reilly 1999). They have been hunted by artisanal fishermen in the Lesser Antilles, where the combined annual catch was in the hundreds until at least the mid-1970s (Reeves et al. 2003). Short-finned pilot whales have also been killed directly in harpoon fisheries in the Caribbean and Indonesia. In the 19th century, whalers off the Azores took pilot whales to compensate for reduced sperm whale catch and American whalers used pilot whales for "practice" for hunting sperm whales (Clarke 1981).
Fisheries bycatch: Pilot whales are taken as incidental catches in several types of fisheries, especially trawls, driftnets, and longlines. Short-finned pilot whales have been taken as bycatch in several fisheries in the North Pacific, including driftnet fisheries for swordfish and sharks and the squid purse seine fishery that operates off the California coast. Sources of bycatch mortality for pilot whales in the Atlantic include interactions with coastal gillnets, bottom and mid-water trawl fisheries, with the highest level of mortality from the pelagic longline fishery (Waring et al. 2002). More recently, most by-catch in the U.S. Atlantic occurs in the pelagic longline fishery. The annual estimated mortality or serious injury (of both species of pilot whales) in this fishery from 2003-2007 was 110 whales (Waring et al. 2009). As a result, the by-catch of pilot whales was addressed by the Atlantic Pelagic Longline Take Reduction Team.
Noise pollution: Short-finned pilot whales, like some beaked whales, are likely to be vulnerable to some anthropogenic sounds, like those generated by navy sonar and seismic exploration (Cox et al. 2006). While conclusive evidence of cause and effect are often lacking, mass stranding events have been spatially and temporally associated with high levels of anthropogenic sound (Hohn et al. 2006).
Pollution: Accumulation of heavy metals, PCB, and DDT can be a concern for these long-lived marine mammals. High concentrations of DDT and PCB have been found in short-finned pilot whales off the U.S. Pacific coast (O'Shea et al. 1980).
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