Globicephala macrorhynchus
The short-finned pilot whale is a distinctive, medium-sized
whale. It has a long, slender body, with a thick, keeled tail
stock. The head is bulbous, and the pronounced melon becomes
exaggerated in mature males and overhangs the rostrum. There
is a small, insignificant beak and wide, short, upwards-slanting
mouth.
The dorsal fin is low and falcate, with a rounded tip, concave
trailing edge, and very broad base. It is located one-third
of the way back from the snout to the tail, and may vary in
shape according to sex and age. The tail flukes have sharply
pointed tips, a distinct notch, and concave trailing edges.
The pectoral flippers have a gently curved leading edge, without
the more noticeable elbow of the long-finned pilot whale’s
flipper, and they are shorter, being less than 15% of the
body length, compared with greater than 16% in the long-finned
pilot whale.
The short-finned pilot whale is predominantly black on the
dorsal surface and flanks, with faint white throat and genital
patches on the ventral surface. There is an indistinct, lighter,
post-dorsal saddle on some individuals, which may vary geographically
(for example, the saddle is absent or only faintly perceptible
on short-finned pilot whales of the eastern tropical Pacific,
although in some individuals, it may be large and conspicuous,
and may be more distinct on short-finned than long-finned
pilot whales. Many populations also have a distinct ‘post-orbital’
stripe, rising up from behind the eye to the leading edge
of the dorsal fin. New-born pilot whales are light grey to
cream coloured, with muted pattern. They begin to darken early
in the first year.
Short-finned pilot whales have seven to nine peg-like teeth
in each row, fewer teeth than the long-finned pilot whale.
Individual short-finned pilot whales may be identified, based
on naturally occurring marks and scars on the dorsal fin and
back, some of which are pigmentation patterns.
Adult short-finned pilot whales range in size from 3.6 to
7.2 m in length. Off Japan, studies indicate that there may
be two morphologically distinct forms, a ‘southern’
form and a ‘northern’ form. The southern form
is smaller than the northern. Northern form: males reached
up to 7.2 m in length and females reached up to 5.1 m in length.
Southern form: males reached up to 5.25 m in length and females
reached 4.05 m in length. There is obvious sexual dimorphism
in short-finned pilot whales, with adult males on average
1.3 times longer than females, and twice as heavy.
Mortality Female short-finned pilot whales may live up to
62 years, and males to around 45 years. Pilot whales are susceptible
to mass stranding, often in large numbers. Killer whales and
large sharks may prey upon them.
Distribution The short-finned pilot whale is widespead in
tropical and warm temperate waters of the Atlantic, Indian,
and Pacific Oceans.
In the eastern North Pacific, the range of the short-finned
pilot whale extends from the tropics, northwards to British
Columbia. They are most abundant off central California and
are commonly observed throughout the Hawaiian Islands.
Off South America, their distribution is poorly known, although
they are thought to be present as far south as Peru and Brazil.
They are common along the Japanese coast southward into the
south Pacific, where the species has been reported from Indonesia
and as far south as Tasmania. Both species of pilot whale
are widespread in the Indian Ocean in both coastal and oceanic
waters, although short-finned pilot whales seem to predominate
in the north and around Sri Lanka, the Seychelles, and Oman.
In the Atlantic, the species has been recorded as far north
as Delaware Bay, United States in the west and France in the
east, but usually is not found north of Bermuda and Cape Hatteras,
North Carolina (USA). They range across the North Atlantic
from North America to Madeira and the Azores, the Canary Islands
and north-west Africa, south to central west Africa. They
have not been reported from the Mediterranean. They are present
in the Caribbean and Gulf of Mexico.
Population
The short-finned pilot whale is considered to be abundant
world-wide, but some populations are depleted. Populations
and abundance of short-finned pilot whales are not well defined,
except off Japan where two morphologically distinct, allopatric
forms have been recognised. Off Japan, the northern form numbers
only an estimated 4,600 animals. The southern form is estimated
to number 53,000 individuals.
Habitat In general, the short-finned pilot whale inhabits
tropical and sub-tropical areas of the Atlantic and Pacific
Oceans. They tend to be oceanic in habit, and generally prefer
deep water. In winter and spring, pilot whales seem to cluster
in squid spawning areas for example, in the southern Californian
Bight, often at the heads of deep submarine canyons. Studies
off the Canary Islands, found that they seem to favour areas
where the sea bed is characterised by high relief, such as
escarpments and sea mounts (rather than basins and plains),
and strong currents which may induce upwelling and support
higher prey densities. In the western North Pacific, the short-finned
pilot whale occurs in waters with surface temperatures above
15 to 16 degrees centigrade and under the influence of the
Kuroshi Current and its tributaries.
Migration Definite migrations have not been documented, but
short-finned pilot whales seem to travel widely. Movements
related to both prey distribution and associated with warm
currents have been noted, for example off northern Japan and
southern California. In both areas, short-finned pilot whales
move into inshore waters at certain times of the year, possibly
following spawning squid. Their distribution may also vary
seasonally in parts of the Caribbean, where they have been
described as a ‘visitor’ during the warmer months
between April and October. It seems to be seen more often
in summer and in greater numbers.
These movement patterns are not noted throughout the short-finned
pilot whales distribution, however. Records from the Indian
Ocean do not indicate any clear temporal pattern of migrations
or seasonal changes in any region. Some populations of short-finned
pilot whales are present year round, such as those in Hawaii
and the Canary Islands.
Feeding Pilot whales are considered to primarily feed on squid,
although they occasionally feed on fish. Off Japan, prey items
included: Japanese common squid, two species of flying fish,
giant octopus, and two other squid species. The stomach contents
of four pilot whales killed as a result of fisheries interaction
in the Southern Californian Bight were all found to contain
beaks of the squid, Loligo, as well as gonatid squid species,
similar to those from the stomachs of deep diving marine mammals
such as sperm whales and elephant seals.
Groups of pilot whales often travel abreast when foraging,
in long lines of individuals, each separated by a few metres.
This is thought to be an effective prey detection strategy.
The movements of short-finned pilot whales probably follow
the seasonal abundance and distribution of the squid, whilst
off central and southern California, there is evidence that
the short-finned pilot whale selectively feeds on the squid
Loligo sp., at least in autumn and winter. Some studies of
stomach contents indicate that pilot whales make deep dives
when foraging.
In captivity, short-finned pilot whales were reported to
feed predominantly at night
Motion Pilot whales may be active at the surface, spy-hopping,
lob-tailing and occasionally breaching. Often, however, they
are relatively unobtrusive at the surface, and do not bow-ride
vessels. When resting, pilot whales merge into groups and
lie almost motionless near the surface. Adult males have been
observed patrolling the perimeter of a loafing pod.
From short-finned pilot whales examined off Japan, the following
information was obtained on lengths and ages upon attainment
of sexual maturity:
- Northern form : Males - 5 to 5.9 m in length (average
5.5 to 5.6 m), and an average age of about 17 years. Age
at asymptotic body length was 25 to 30 years. Females -
Fifty percent of females examined were sexually mature at
between 3.9 and 4.0 m in length. The average age at attainment
of sexual maturity was 8.5 years (range 5.5 to 11.5 years).
Age at asymptotic body length was 25 to 30 years.
- Southern form : Males - 4.22 m in length and at a similar
age to the northern form animals. Age at asymptotic body
length was approximately 27 years. Females - mean body length
was 3.16 m. Average age at attainment of sexual maturity
was 8.5 years (range was 5.5 to 11.5 years). Age at asymptotic
body length was 22 years in ‘southern’ females
Off Japan, the mating season was found to be August to November,
peaking in October/November for the northern form, and January
to August, peaking in May, for the southern form.
It has been estimated that gestation may last for 14 to 15
months, (although some scientists consider that a 12-month
gestation may be more likely). The length of lactation varies
considerably between individuals, but usually lasts at least
two years. Calves are generally about 6 months old when they
begin to take solid food, although they often continue to
suckle until up to the age of at least three years. The calves
of older females may be nursed for considerably longer than
the minimum of two years, and the care of successive offspring
frequently overlaps. Some males of up to 14 years old were
found to be suckling. The mean reproductive cycle is calculated
to be between 4.5 and almost 6 years.
Reproductive activity of females is thought to decline with
increasing age, and probably usually ceases at around 37 years
of age. There are believed to be significant numbers of post-reproductive
females in the population. Reproductive senescence occurs
among some females aged over 28 years, although one female
was found to be lactating at 43.5 years old.
Short-finned pilot whales are gregarious animals and rarely
found alone. Groups range in size, up to several hundred animals,
but more often they are found in pods of 15 to 30 individuals.
The schools are composed of adult males and females, spanning
the entire range of age and reproductive status, and immature
animals of both sexes. It appears, from initial studies, that
pilot whales live in stable, cohesive, female-based schools.
The mother-calf association is thought to last until around
the age of sexual maturation in males (at 15 to 22 years)
and perhaps after maturation in females (7 to 12 years). Old
and post-reproductive females comprise a significant part
of the school, and probably contribute towards its maintenance
and the survival of its younger individuals.
The cohesiveness of the schools is evidenced by the frequency
with which they are involved in mass stranding incidents.
Furthermore, maternal investment is substantial.
Some females have a post-reproductive life span of 20 to
30 years (the mean is 14 years), which is very unusual in
wild animals. There is evidence of both non-reproductive mating,
and extended periods of lactation in post-reproductive females.
This might enhance school stability and increase reproductive
success of female kin. There is no morphological evidence
for interspecific fighting between males in the short-finned
pilot whale, such as is known for other species such as the
sperm whale.
Herds of pilot whales appear to be highly organised; while
foraging or travelling, a herd may be sub-divided into closely
knit groups of adult males, juveniles, or females with young.
Associations between social behavioural context and vocalisations
have been demonstrated. Simple whistles were found to predominate
when several pods were spread out during travel. These whistles
probably play an important role in maintaining contact and
co-ordinating movements between individuals. More complex
whistles and pulsed sounds were heard when pilot whales were
socialising or in a state of excitement such as during encounters
between two pods. During periods of rest, whales were mainly
silent.
Short-finned pilot whales are often found associated with
other species of cetaceans, including northern right whale
dolphins, Pacific white-sided dolphins, bottlenose dolphins,
sperm whales, Risso’s dolphins, common dolphins, and
various Stenella spp.
A poorly-known species. The short-finned pilot whale generally
uses higher frequency sounds at lower levels than the long-finned;
this may be related to their smaller size. Maximum source
level is 176 dB re 1 mPa @ 1m (all sounds).
- PULSIVE : Clicks with energy up to 140 kHz. Pulsed calls
are also produced; no analysis yet reported.
- TONAL : Whistles between 2-12 kHz.
Short-finned pilot whales have been hunted throughout their
range, the largest catches being made off Japan, where in the
early 1980’s, following a rise in the price of whale meat,
some Japanese small-type whaling vessels resumed the hunting
of short-finned pilot whales. Several hundred pilot whales are
thought to have been killed annually, although reported numbers
of takes are unreliable. The species is also hunted throughout
the Lesser Antilles, where they are the principal quarry of
small-scale hunts for cetaceans. There is no formal system for
monitoring or reporting cetacean catches on the islands and
official catch records are thought to greatly under-represent
the actual catch. Until recently it is estimated that several
hundred pilot whales were killed each year. There are concerns
for the status of this little known stock.
Elsewhere, short-finned pilot whales are taken as a minor target
species in various small cetacean fisheries. They are affected
by incidental capture in fishing gear in several areas.
Recent studies have revealed that both long-finned and short-finned
pilot whales in the eastern Atlantic, are widely infected
with morbillivirus infection. This may be an enzootic infection,
and it has been suggested that, through mixing with other
odontocetes, pilot whales could act as vectors throughout
the Atlantic. It has also been postulated that clinical morbillivirus
infection may precipitate mass strandings of highly social
odontocetes. Links between deaths of cetaceans through morbillivirus
infection and pollutants such as PCB’s (which may suppress
the immune system) have also been proposed. In the Mediterranean,
striped dolphin populations suffered a major morbillivirus
enzootic between 1988 and 1991.
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