Globicephala macrorhynchus, Gray, 1846

Russell A. Mittermeier & Don E. Wilson, 2014, Delphinidae, Handbook of the Mammals of the World – Volume 4 Sea Mammals, Barcelona: Lynx Edicions, pp. 410-526 : 517-518

26.

Short-finned Pilot Whale

Globicephala macrorhynchus

French: Globicéphale tropical / German: Kurzflossen-Grindwal / Spanish: Calderén de aleta corta

Other common names: Pacific Pilot Whale, Southern Blackfish, Southern Pothead Whale

Taxonomy. Globicephalus macrorhynchus Gray, 1846 ,

“South Seas.”

Taxonomy of G. macrorhynchus is currently in dispute. Two genetically, morphologically, and geographically distinct forms found off northern and southern Japan suggest that G. macrorhynchus comprises two or more species or subspecies, but additional research is required to confirm this. Monotypic.

Distribution. Tropical, subtropical, and warm temperate waters worldwide from ¢.50° N to ¢.40° S, including the Red Sea, but excluding the Mediterranean Sea and Persian Gulf.

Descriptive notes. Total length 720 cm (males) and 550 cm (females); weight 3500 kg (males) and 1500 kg (females). Neonates are 140-190 cm long and weigh 40-80 kg. Like the Long-finned Pilot Whale ( G. melas ), the Short-finned Pilot Whale has bulbous head, small beak, and deep tailstock. Key features that distinguish it from the Longfinned Pilot Whale are its shorter flippers (14-19% of total body length). Falcate dorsal fin with wide base is positioned approximately one-third of body length back from snout. Skin pigmentation ranges from dark gray or brown to black. Adults possess white or pale gray patches on chest and urogenital area, behind dorsal fin, and above eyes. Thin white mid-ventral line mayjoin chest and urogenital patches. Young, sexually immature individuals have paler skin than adults. Like the Long-finned Pilot Whale, the Short-finned Pilot Whale is very sexually dimorphic in size, with males larger than females. Males have more bulbous, often square-shaped rostra, larger dorsalfins, and longer flippers than females. Each jaw contains 7-9 pairs of teeth. Two distinct forms found off northern and southern Japan differ slightly in size (the northern form is larger) and cranial and external morphology.

Habitat. Global tropical, subtropical, and warm temperate waters. Although the Short-finned Pilot Whale is found in coastal and offshore waters, it appears to prefer deeper (600-1000 m) offshore habitat over outer continental slopes. It is mostly nomadic, but a few resident populations are found off coastal California and Hawaii. The two distinct forms found off northern and southern Japan also appear to be resident. Populations of Long-finned Pilot Whale are known to have occupied waters offJapan until the 12" century, and it has been hypothesized that Short-finned Pilot Whales have since expanded their distribution in this area as a result of the former species’ extirpation.

Food and Feeding. The Short-finned Pilot Whale prefers to forage on deep-dwelling species, primarily cephalopods, and uses energetic “sprints” to chase down targeted prey. Because most cephalopods move,closer to the water’s surface at night, the Shortfinned Pilot Whale is a nocturnal hunter and most actively feeds at dawn and dusk at depths of 300-500 m. Foraging dives can last up to 27 minutes. Documented prey species include European flying squid (7odarodes sagittatus), glass squid (Cranchia sp. and Megalocranchia sp.), common arm squid (Brachioteuthis riser), cranch squid (7aonius pavo), reverse jewel squid ( Histioteuthis reversa ), and Bean's bigscale (Scopelogadus beanit).

Breeding. Mating system of the Short-finned Pilot Whale is likely polygynous. Breeding peaks in autumn and winter in the Northern Hemisphere and in spring and autumn in the Southern Hemisphere. Gestation lasts 15-16 months. The birthing interval of the Short-finned Pilot Whale, as with the Long-finned Pilot Whale, is among the longest known in cetaceans, at 3-5 years. This long span accommodates an unusually long lactation period that lasts c.3 years on average, and it likely plays an important role in reinforcing social bonds. Males reach sexual maturity later (13-17 years) than females (8-9 years). Females live almost twice as long (up to 63 years) as males (30-45 years), and post-reproductive female longevity is common, occurring at ¢.40 years. Females may lactate for up to 15 years after they are no longer reproductive, an adaptation that likely improves survivability of closely related young individuals such as grandoffspring.

Activity patterns. Because the Short-finned Pilot Whale primarily forages at night, dives tend to be shallower during the day rarely exceeding 100 m. Behaviors during the day consist primarily of socializing, resting, and traveling. While hunting or traveling, individuals in groups will organize themselves into a long “chorus line” that can be up to 3-2 km wide and only a few individuals deep. While resting, the group will remain relatively stationary, with individuals rafted closely together, almost touching. The Short-finned Pilot Whale is only moderately active aerially. Groups may “porpoise” while traveling, and individuals may spy-hop, but breaching is less common.

Movements, Home range and Social organization. Both species of pilot whales are highly social and have stable, matrilineal social structures. The Short-finned Pilot Whale will travel in groups of 15-50 individuals, although large groups of several hundred individuals have been documented. In the eastern Pacific Ocean, the Shortfinned Pilot Whale occurs in mixed-species groups with a variety of other cetacean species, including the Common Bottlenose Dolphin ( Tursiops truncatus ) and various species of Stenella in tuna ( Thunnus )—dolphin aggregations. Social vocalizations have a mean frequency of 7870 Hz, higher than vocalizations of the Long-finned Pilot Whale at 4480 Hz. Matrilines tend to have a slightly female-biased sex ratio and consist of a matriarch and her immediate kin. Strong natal group philopatry is exhibited by both sexes, but by males especially. Like the Long-finned Pilot Whale, male Short-finned Pilot Whales will mate during temporary aggregations of separate family groups but will otherwise remain in their own matrilines for their entire lives. Matrilines also have distinct call repertoires, a cultural trait expected from a species with stable social structure, and similar in nature to the clan-specific dialects of another matrilineal delphinid such as the Killer Whale ( Orcinus orca ). Like the Long-finned Pilot Whale, the Shortfinned Pilot Whale is also prone to mass stranding. Their strong social bonds contribute to this vulnerability because a leading individual that makes a navigational error is likely to be followed instinctively by the rest of the group. This kind of conformity has even resulted in individuals restranding after being pushed back out to sea. Cases of mass stranding may be triggered by individuals who have had their navigational abilities impaired by acoustically related injuries (e.g. from seismic surveys), but in regions where they are regular, such as Hawaii, Puerto Rico, and the British and US Virgin Islands, coastal configuration and bottom topography may be to blame, either by being complex to navigate or by interfering with local geomagnetic contours. The Short-finned Pilot Whale does not appear to be migratory. It is found throughout the year in some regions, such as off Hawaii and the Canary Islands, although recent studies suggest there may be several populations in Hawaii with varying degrees ofsite fidelity. In other regions such as off southern California, Short-finned Pilot Whales have seasonal inshore—offshore movements that are likely related to fluctuating cephalopod abundance.

Status and Conservation. CITES Appendix II. Classified as Data Deficient on The IUCN Red List. Taxonomy of the Short-finned Pilot Whale is currently in dispute, and if new species or subspecies are classified, they may warrant a threatened listing. Global abundance estimates and trend data are not currently available for the Short-finned Pilot Whale, but they do exist for several areas. OffJapan, the northern form is estimated at 4000-5000 individuals and the southern form at ¢.14,000 individuals. There are ¢.7500 individuals off the Philippines, ¢.589,000 individuals in the eastern Pacific Ocean, ¢.8846 individuals off Hawaii, ¢.2388 individuals in the Gulf of Mexico, and ¢.300 individuals off the west coast of North America. The most serious threats are direct and incidental catch. In Japan, several hundred Short-finned Pilot Whales were killed annually in drive fisheries for centuries, but the national quota is now 50 ind/ year. Nevertheless, in recent years, the southern form has sustained a higher catch rate than the northern form (1755 southern individuals were taken in 1982-1985), and it has decreased drastically in abundance since the 1980s. Its population is now considered “depleted.” A fishery operating off the Lesser Antilles takes ¢.220 ind/year, and unmonitored fisheries in Indonesia and Sri Lanka also are known to kill the Shortfinned Pilot Whale. It is harpooned illegally and opportunistically in fisheries from the Visayas, Mindanao, and Philippines. In these direct catches, meatis usually sold as food for human consumption or used as bait in other fisheries. The Short-finned Pilot Whale also is taken incidentally in both Atlantic and Pacific waters off the USA, primarily in squid fisheries, although catch rates currently do not exceed legally allowable limits. In the western Pacific Ocean, 350-750 individuals are killed incidentally every year in passive nets or traps set by Japanese fisheries. Effect of mortality from incidental catch on populations has not yet been quantified, and incidental catch is probably underestimated in most of the distribution of the Short-finned Pilot Whale due to a lack of monitoring. For example, an unknown number of Short-finned Pilot Whales are caught annually in pelagic driftnets off the east coast of Taiwan. Gunshot and spear wounds observed on individuals off Puerto Rico and the US and British Virgin Islands also suggest that aggressive fishermen are a threat in some regions. Contaminant-related health problems may also be an issue for some populations of Short-finned Pilot Whales. High concentrations of DDT and PCB have been found in individuals off the west coast of the USA. Avoidance behavior by the Short-finned Pilot Whale also has been observed in response to whale-watching vessels, suggesting that tourist activity may have negative effects in some areas. The Short-finned Pilot Whale’s propensity for mass stranding, and its preference for deep-dwelling prey, mean that it is particularly vulnerable to loud anthropogenic noise. Large-scale military exercises around Taiwan in 2004, for example, coincided with a series of stranding events of Short-finned Pilot Whales.

Bibliography. Barlow (2006), Bernard & Reilly (1999), Bustamante et al. (2003), Davis et al. (1998), Dolar (1999), Dolar et al. (1994), Fullard et al. (2000), Hernandez-Garcia & Martin (1994), Hindell (2008), Jefferson et al. (2008), Kanaji et al. (2011), Mahaffy (2012), Mazzuca et al. (1999), Mignucci-Giannoni et al. (1999), Mintzer et al. (2008), Olson (2009), Sinclair (1992), Taylor et al. (2011), Wang & Yang Shihchu (2006, 2007), Weir (2008).

Figures

On following pages: 33. Commerson’s Dolphin (Cephalorhynchus commersonii); 34. Chilean Dolphin (Cephalorhynchus eutropia); 35. Heaviside's Dolphin (Cephalorhynchus heavisidii); 36. Hector’s Dolphin (Cephalorhynchus hector).

Distribution. Tropical, subtropical, and warm temperate waters worldwide from ¢.50° N to ¢.40° S, including the Red Sea, but excluding the Mediterranean Sea and Persian Gulf.