Kurzflossen-Grindwal

 

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Klassifikation:

Weltweite Population

Beschreibung und Lebensweise

Physical Description
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.

Natural History 
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.

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.

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.

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Status der Art

Status 
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.

 
Threats to the Species 
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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Autor und Quellen

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