How old do spinner dolphins get
East Pacific dolphin
The East Pacific Dolphin (Stenella longirostris) counts within the dolphin family (Delphinidae) to the genus of spotted dolphins (Stenella). In English this will be dolphin Spinner Dolphin called. The scientific name "longirostris" is a reference to the long snout of this species.
Appearance and dimensionsThe East Pacific dolphin is a rather small dolphin and reaches a body length of 130 to 235 centimeters and a weight of 23 to 78 kilograms. The average length is around 182 centimeters with a weight of 33 kilograms. The physique is extremely slim. Dorsally, the East Pacific dolphin is dark gray in color. Laterally a light gray, ventrally a whitish color, which is speckled dark. Geographically, both the color and the size of the animals vary greatly. The beak is long and narrow, on the side of the head a dark colored band runs from the eyes to the pectoral fins. The upper jaw has between 44 and 64 teeth per upper jaw half and between 42 and 62 teeth per lower jaw half.
Way of life
East Pacific dolphins live in sociable schools that can contain more than 1,000 individuals. An average school, however, has significantly fewer animals and is mostly made up of family groups. The composition of a school is definitely variable and by no means fixed. Larger schools can also split into subgroups. Above all, within a group, the relationship between a mother and her offspring is very close and intimate. Calves usually stay with their mother until they are two years old and learn from her everything they need for an independent life. Even if East Pacific dolphins are mainly active during the day, they only look for food at night. East Pacific dolphins, like many dolphins, exhibit interesting behavior. You catapult yourself completely out of the water with mighty jumps. The meaning or purpose of these jumps has not yet been scientifically researched.
The German synonym, East Pacific dolphin, is misleading, as this species of dolphin with four subspecies occurs worldwide in all tropical and subtropical oceans. They live mainly on the open sea, but are sometimes also found on the coasts of the mainland or individual islands such as Hawaii. In any case, pelagic waters are preferred. East Pacific dolphins only occur in waters with water temperatures of 25 degrees Celsius and more. The most widespread is the nominate form Stenella longirostris longirostris. It occurs in all three oceans. Stenella longirostris orientalis can only be found off the coast of western Central America. The same applies to the subspecies Stenella longirostris centroamericanawhich, however, only occurs near the coast in western Central America. Stenella longirostris orientalis also lives on the high seas. The fourth subspecies, Stenella longirostris roseiventris occurs in a small area in Southeast Asia. Here the animals live off the coast of Thailand and around Timor. To the south, the distribution area of this subspecies extends to Indonesia and northern Australia.
The population of all populations is around 900,000 individuals today. However, the estimates vary greatly depending on the author. The stocks were subject to heavy hunting for decades. But hundreds of thousands of animals ended up as bycatch in tuna nets. The smallest population is Stenella longirostris roseiventris, which lives in Southeast Asia and is estimated to be around 30,000 to 35,000 animals. Depending on the occurrence, the East Pacific dolphins make seasonal migrations. This is especially true for subtropical waters, where it gets too cold in winter. This applies, for example, to the waters off New Zealand or South Africa. Otherwise, there are only smaller hikes when looking for food.
The natural carnivores of the East Pacific dolphins are likely to include above all else Great killer whales (Orcinus orca), Killer whales (Pseudorca crassidens) and some species of shark like that White shark (Carcharodon carcharias). Perrin also suspects that short-finned pilot whales (Globicephala macrorhynchus) and minke pilot whales (Feresa attenuata) Hunt the East Pacific Dolphins. Due to the group formation, only those animals fall victim to carnivores that stay outside the group or live solitary. The infestation by ecto- and endoparasites such as roundworms is far worse (Nematoda). These pathogens can easily cause fatal diseases and the dolphins inevitably die.
As pure carnivores, East Pacific dolphins feed mainly on bony fish (Osteichthyes), which are usually up to 20 centimeters in length. But there are also cephalopods (Cephalopoda) like squids (Teuthida) and small decapods (Decapoda). The prey animals are hunted down to depths of 200 to 300 meters. High on the menu, depending on the area of distribution and habitat, are lantern fish, for example (Myctophidae), Luminous fish (Phosichthyidae), Unicorn cod (Bregmaceros), Pearl eyes (Scopelarchidae), Medusa fish (Stromateidae), Barracudinas (Paralepididae), Gut fish (Carapidae), Soldier and hussar fish (Holocentridae) and Brotulas (Bythitidae).
Ecology, hazard and protection
In the IUCN Red List, the East Pacific dolphin is now listed as not endangered (LC, Least Concern). The Washington Convention on Endangered Species places the species in Appendix II under special protection. In the past, the East Pacific dolphin was hunted on a massive scale. The decline in stocks assumed critical values. After the species was placed under protection, the populations began to slowly recover, but this is still ongoing. The species is still hunted today in large parts of Southeast Asia. As a rule, the animals are harpooned. However, bycatch is far worse than direct catch. East Pacific dolphins are very curious dolphins and often get caught in the fishermen's trawls. Up to 100,000 East Pacific dolphins get caught in such trawls every year. Novel nets have been able to reduce bycatch in recent years, but not completely eliminate it. In addition, climatic changes, shrinkage due to predators, stranding and separation of the calves from their mothers also have a negative effect on the population.
The general pollution of the coastal waters with heavy metals and pesticides such as DDT or PCB also poses major problems for the East Pacific dolphins. The poisons have a direct or indirect effect on the animals through food. Ecotourism is also increasingly taking effect, which is expressed primarily through dolphin watching. Today humans are penetrating more and more into the habitats of the East Pacific dolphins. It has already been reported that in the densely populated coastal areas of Central America or Southeast Asia, East Pacific dolphins were injured by the propellers of ships and boats. The mere presence of ships and boats in the dolphins' native waters is causing unrest in schools. They become nervous, are disoriented and profound interventions in social life cannot be ruled out either. It is not uncommon for these causes to lead to the death of the animals. East Pacific dolphin beaching is also common in densely populated habitats. The damage caused by engine noise should not be any less serious. This has a particular effect on hearing and orientation skills. Even the popular dolphin watching has a negative impact on populations.
Literature and sources
- Ronald M. Nowak: Walker's Mammals of the World: v. 1 & 2. B&T, edition 6, 1999, (engl.) ISBN 0801857899
- Don E. Wilson & DeeAnn M. Reeder: Mammal Species of the World, a Taxonomic & Geographic Reference. J. Hopkins Uni. Press, 3rd ed., 2005 ISBN 0801882214
- David Macdonald: The great encyclopedia of mammals. Ullmann / tandem ISBN 3833110066
- Hans Petzsch: Urania Animal Kingdom, 7 Vols., Mammals. Urania, Stuttgart (1992) ISBN 3332004999
- Mammals. 700 species in their habitats. Dorling Kindersley, 2004. ISBN 383100580X
- Karl Müller: Whales and dolphins. Karl Müller Verlag, Kön (2004) ISBN 3833601329
- William F. Perrin: Stenella longirostris, The American Society of Mammalogists, 1998
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