Northern elephant seal
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Northern elephant seal, bull with several females |
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| Mirounga angustirostris | ||||||||||||
| ( Gill , 1866) |
The northern elephant seal ( Mirounga angustirostris ) is one of two species of elephant seal . He is in the eastern Pacific along the coast of North America from Baja California to Alaska and the Aleutian spread, with the colonies of the animals to the area of Baja California and the California coast limit. The animals spend most of their lives in the sea, only when they change fur and during the three-month mating and littering period do they form large colonies on the coast and on offshore islands.
Together with the somewhat larger southern elephant seal ( Mirounga leonina ), the northern elephant seal is one of the largest species of seals and at the same time the largest species of predator . The bulls reach a height of over four meters and a weight of up to 2,500 kilograms. The females are significantly smaller with a maximum height of three meters and a weight of 600 to 800 kilograms. Northern elephant seals feed primarily on fish and cephalopods , while the killer whale ( Orcinus orca ) and the great white shark ( Carcharodon carcharias ) play a role as potential predators .
After the animals nearly became extinct due to heavy hunting in the 19th century, they were placed under protection in the United States in the early 20th century and have since recovered well in numbers. Today the species is no longer endangered, the population is estimated at over 170,000 animals.
features
general characteristics
The elephant seals show a strong sexual dimorphism in their body size and appearance . The bulls of the northern elephant seal reach an average length of 3.80 to 4.10 meters with a weight of about 1800 kilograms and a maximum length of 4.20 meters with a weight of 2500 kilograms. With an average length of 2.80 to 3.00 meters and an average weight of 600 to 800 kilograms, the females are significantly smaller than the males. The animals have their maximum weight on arrival in the colony in late autumn, after having spent most of the summer and autumn foraging for food. During the three months in the colony, they lose about half their weight. Weight can fluctuate a lot and after giving birth, females can lose half their weight within around 25 days of breastfeeding .
The body color of the adult animals is brown to dark brown on the back and light sand-colored on the belly. The young animals are black after birth and during the breastfeeding period for the first month of life, then the coat changes and they become silver-gray and later chocolate-brown on the back and sand-colored on the abdomen. Especially in the males, the skin on the neck and throat thickens and becomes keratinized. The coat consists of individual, very short and coarse hairs. Once a year there is a change of coat on land, in which the animals rub off the hair and the top layer of the skin in larger patches and replace them with the new epidermis underneath. The new hair growth begins a few days after the renewal. The change of coat, which takes place in the young animals and females in April to May, the young males in late May to June and the adult males in July to August, takes place during a rest on land lasting several weeks.
Like all seals, elephant seals have limbs that have been transformed into fins. As with all seals, the eyes are very large in order to have the maximum possible view in the water and at greater depths. The male's nose begins to enlarge into a proboscis at the age of three to five years. It develops into a conspicuous male secondary sexual characteristic by the time it reaches sexual maturity between the ages of eight and ten. The proboscis increases the intensity of the males' calls during the mating season.
The northern species differs from the southern elephant seal in that it is somewhat smaller and the sex differences are less extreme; the trunk of the male, however, is larger (up to 30 cm) than that of the southern elephant seal.
Features of the skull and skeleton
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In both sexes, the teeth are primarily designed to grab and hold the prey, which is then swallowed whole. The animals have two incisors on each side in the upper jaw , one strong canine , three premolar teeth and a variable number of molars . There is only one incisor in the branch of the lower jaw. The animals have a total of 30 teeth, but the postcaninae are almost completely inoperable and the large canines help hold the prey in place. The canines are enlarged and sharp in both sexes, but in the males they are much stronger than in the females. The strong canine teeth are also used by the males in rival fights during the mating season.
The spine consists of 39 to 40 vertebrae , 7 of which belong to the cervical spine , 15 to the thoracic spine , 5 to the lumbar spine , 3 to the sacrum and 9 to 10 to the tail spine . Only the anterior and posterior vertebrae have a ventral keel and the slightly flattened lumbar vertebrae can have a second keel, thereby forming a ventral pit. The bone density is comparatively low as an adaptation to the swimming and diving lifestyle.
Genetic traits
The northern elephant seal has a karyotype made up of 34 chromosomes . The genetic variability within the species is very low and no polymorphism could be found in studies of various blood proteins . This low variability is attributed to the effects of the near-extermination of the animals and the re-establishment from a comparatively small founder population with a corresponding genetic drift . By examining microsatellites , short non-coding sections of the DNA , the low variability could be shown again, at the same time it was discussed that the distribution of the population to the different mating beaches and above all the local loyalty of the animals to their home beaches leads to a higher genetic level Diversity can come between the animals of the northern beaches and those of the southern.
distribution and habitat
The northern elephant seal lives in the northeastern Pacific and north of the eastern central Pacific to the western edge of the Aleutian Islands . In rare cases, individual animals can reach the Bering Strait , Hawaii or the north of the Japanese islands .
The animals spend about 90% of their life in the sea and only form colonies on land during the littering and mating season as well as when changing their coat, in which a large number of the animals collect. The colonies are located along the North American west coast on several offshore islands and on mainland places from Baja California , Mexico , to Northern California . A few colonies are formed north of California on the coasts of Oregon , Washington, and southern British Columbia .
The coastal areas used by the northern elephant seal for colony formation are sandy to stony or muddy bank regions and offshore islands. A total of more than 15 northern elephant seal colony sites are known, with Año Nuevo Island in central California between San Francisco and Santa Cruz being one of the largest. The Piedras Blancas Rookery near San Simeon is the largest mainland colony .
Way of life and ecology
Northern elephant seals spend most of their lives in the ocean, with only occasional surfacing. They spend 85 to 90% of their life diving underwater. On average, they dive to a depth of around 500 to 600 meters, the known maximum depths are around 1500 meters. They are able to spend 20 to 70 minutes underwater during a dive. In the sea they are solitary animals and males and females live and hunt independently.
hikes
The elephant seals visit their colonies twice a year. The mating and littering season takes place from December to March, and later in the year the animals come ashore to change their fur, depending on their age and sex. Then they move to the North Pacific and the Gulf of Alaska . The adult males migrate further north and west than the females, whereby individual migrating animals have also been spotted on the coasts of Hawaii , in Japan and on the Midway Islands as well as in the area of the Bering Strait .
There are big differences between the sexes between migration habits and hunting behavior. Investigations of the migratory behavior of the animals in the Año Nuevo State Park via satellite observations and transmitters on the animals for telemetry showed that the males directly after leaving the beaches at a speed of around 90 kilometers per day (± 27 km / d) swim north to the marine areas from the coast of Oregon to the western Aleutian Islands , covering distances of around 540 to almost 5,000 kilometers. They stay in these areas for most of their stay in the sea and also return to the same areas on later migrations. The females, on the other hand, move to a much wider area in the northeastern Pacific and spend the time in a region between 38 and 60 ° north latitude and the coast to 172.5 ° east longitude. They concentrate their foraging in areas above the deep sea, in which they significantly reduce their migration speed and usually stay for 3.5 days before going to further hunting regions. Like the males, after leaving the beaches, the females also move in the same direction as in previous years, but are less defined with regard to the specific diving areas and change the directions of migration.
Diet, diving behavior and water balance
The Northern elephant seals feed on cephalopods in mesopelagial as well as bone and cartilaginous fish such as small sharks and rays on the seabed. They hunt their prey on their dives. The males usually dive in the area of the continental shelves down to the sea floor at depths of 300 to 400 meters. The females, on the other hand, hunt pelagically in the open sea at depths of up to 800 meters by briefly ascending and descending from the sea floor several times. According to these hunting methods, the prey animals of the males and females differ. While the males mainly prey on benthic sharks and rays, the females feed mainly on free-swimming cephalopods such as octopuses and squids . This different diet is discussed as the cause of the enormous size differences between the sexes. Both sexes spend very short times on the surface of the ocean to breathe. The dives, on the other hand, can last between 12 and 60 minutes, depending on the age, sex and size of the animals. Males usually dive longer with an average of about 30 minutes and more, while females dive deeper and in extreme cases can penetrate to depths of 1,600 meters. A large proportion of the captured cephalopods have bioluminescent organs and are hunted visually accordingly.
The diving behavior of the northern elephant seals is designed in such a way that they have minimal energy consumption and can also use the diving phases as rest phases. According to observations of young animals equipped with transmitters, the animals can sink backwards while diving without active swimming movement and move at irregular intervals by making their body wobbly and thus slowing down the sinking and lengthening it like a loop. It is believed that this will prevent you from sinking too low and at the same time give you enough time to rest. During this time the animals are probably not actively looking for prey, at the same time they avoid encounters with predators, which are usually active in the upper 150 meters of the water column.
During the times that elephant seals spend most of their time on land for mating, rearing young and changing fur, they do not eat and fast. During this time, they gain their energy from the built-up fat reserves that have accumulated in their body and break them down accordingly. The females in particular reduce their activities and movements to a great extent in order to minimize energy consumption and pass the reserves on to the young animals in particular. The males use their energy reserves primarily for their rival fights and for mating with as many females as possible.
The water intake of the animals takes place exclusively through food and through fat breakdown, at the same time they are physiologically adapted to minimal water loss . Your urine is highly concentrated to prevent excessive water loss.
Reproduction and development
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Bull rivalry of the Northern Elephant Seals
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Northern elephant seals mate on land, where the animals meet in the colonies on the mating beaches. The adult males and females arrive at the mating beaches between December and February, with the adult and sub-adult males arriving earlier than the females. They reach the beaches in December and early January and establish a ranking among themselves, which also determines the distribution on the beach. The battles for ranking will take place throughout the mating season. The females come to the beach from January to the end of February and females pregnant from the previous year give birth to a single young about 7 to 8 days after their arrival. In the next 27 days or so , the young animals are breastfed by the mothers, after which they ovulate and are mated by the bulls shortly afterwards.
The animals are distinctly polygynous and the dominant bulls mate with several females, which they flock around. Since the females do not arrive and give birth synchronously and are therefore not ready to mate synchronously, the mating season lasts from January to March. Since the females can move freely and at the same time the males do not have full control over them, there is no fixed harem of the bulls. During the entire mating season, all males try to keep control over as many females willing to mate as possible. The less dominant bulls are pushed to the edge of the colony and regularly try to mate with the females. This leads to aggressive attacks from the dominant males and fights between the males in order to gain control of the respective harem. If a strange male tries to mate a female in a harem, the harem emits a warning call that attracts the dominant male. If the less dominant male defends himself, sometimes brutal rival fights ensue, in which young animals lying in the vicinity can also be crushed.
When a bull wants to mate with a female, it places one of its pectoral fins over the female, grabs it with its teeth in the neck and begins mating . If the female defends itself, the bull climbs on it with its heavy body so that it can no longer move. The probability of an annual pregnancy for the females is around 95%. After just two days, the will to mate and the willingness to conceive already decline again.
After mating and fertilization of the ovum , this remains usually for two to three months as a blastocyst freely floating in the uterus before it attaches itself to the uterine wall and the embryonic development continues. The gestation period is about eleven months of delay while the actual growth and development of the embryo takes only about seven to eight months. Each female only gives birth to one young. The newborn pups are about 1.25 meters long and weigh 30 to 40 kilograms. The young are born in long, woolly black fur made from lanugo hair , which they lose after 4 to 5 weeks. Then they get the typical short fur of the adult animals.
The young are breastfed for about 25 days, after which the adult animals leave the colonies, while the young do not leave the coasts until April or May. The females reach sexual maturity after around 2 to 4 years, depending on growth and food availability in the first few years. You can then give birth to a young once every year, whereby about 8 to 20% of the females can also abandon each year. The males only reach sexual maturity after 6 to 7 years, but due to the hierarchies and ranking on the mating beach, they can usually only mate successfully after 8 to 10 years. The average maximum age of the males is about 12 to 14 years, that of the females about 18 years.
Predators and parasites
The predators of the elephant seals include the killer whale ( Orcinus orca ) and large species of shark, especially the great white shark ( Carcharodon carcharias ). The latter is relatively common due to the large seal colonies of elephant seals , harbor seals and sea lions on the west coast of California; Due to the comparatively high density of great white sharks and regular shark encounters, this region is known as the “ Red Triangle ” (German: “Red Triangle”). The sharks usually hunt young elephant seals when they return to the colonies in the early years. They patrol at depths of seven to ten meters and attack the seals swimming on the water surface from below. Elephant seals can also be attacked by the small cigar sharks , which bite into the animals and tear pieces of skin and meat from their skin.
Along with the killer whale, the great white shark is the main predator of the elephant seals.
Female elephant seal with the characteristic scars of cigar shark bites.
Because of their smaller size and pelagic way of life, the females are exposed to greater predatory pressure than the males. They avoid this pressure by looking for food in areas further away from the coast , where fewer predators live, while the males can also live in areas near the coast with a high density of predators.
The northern elephant seal can have various commensals and parasites . Thus, various types of were mainly on the skin of younger animals barnacles as Conchoderma auritum and Conchoderma virgatum and barnacles of the species Lepas pacifica , Lepas Anatifera and Lepas hilli identified. The alga Navicula grevilei can also occasionally be found on the skin. In the stomach and intestines of northern elephant seals were simplex Anasakis , decipiens and Contracaecum osculatum three different types of roundworms and flukes Cryptocotyle lingua and Pricetrema zalophi found added Zalphotrema hepaticum from the liver and the nematodes Parafilaroides SEPC. and Ostostrongylus circumlitus from the lungs of the animals. In the nasal concha of elephant seals there are often mites of the species Halarachne miroungae, which is specific to elephant seals, and scratch worms of the species Corynosoma bullosum have also been detected.
Taxonomy and systematics
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Phylogenetic system of dog seals according to Higdon et al. 2007
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The northern elephant seal was first scientifically described in 1866 by Theodore Gill under the scientific name Macrorhinus angustirostris . John Edward Gray , however, had already described the genus Mirounga for the southern elephant seal in 1827 and named the northern elephant seal as Morunga angustirostris in 1871 . In the genus Mirounga ordered Daniel Giraud Elliot in 1904 for the first time the northern type one. Wilhelm Peters assigned the northern elephant seal to the genus Cystophora and thus placed it in the direct relationship of the folding cap ( Cystophora cristata ) and Lionel Walter Rothschild described it in 1910 as a subspecies and nominate form of the southern elephant seal and called it Miorunga leonina leonina . Gill gave “ California ” as Terra typica , in 1942 this information was specified by A. J. Poole and V. S. Schantz with Bartholomews Bay in Baja California , Mexico , and in 1958 by V. B. Scheffer with Bahía Tortola in Baja California.
Together with the southern elephant seal, the northern elephant seal forms the genus Mirounga , which is assigned to the dog seals . The position within the dog seals is unclear and has been discussed regularly. In 1983 King put forward the theory that is still often cited today that the elephant seals are most closely related to the monk seals ( Monachus ) and that both were particularly original representatives of the dog seals . On the other hand, Bininda-Emonds and Russell could not find any evidence of such a close relationship in 1996, but confirmed the basic position of the elephant seals in the dog seal system. Based on molecular biological results from the year 2007, the elephant seals are currently a sister group of the Lobodontini combined species group from Ross Seal ( Ommatophoca rossii ), Crabeater ( Lobodon carcinophaga ), leopard seals ( Hydrurga leptonyx ) and Weddell ( Leptonychotes weddellii considered) , The monk seals are considered to be a sister group of both taxa, elephant seals and lobodontini.
No subspecies are distinguished within the species. The generic name Mirounga is derived from "miouroung", the name for southern elephant seals in a language of the Australian Aborigines. The species name angustirostris is derived from the Latin words "Angustus" for "narrow" and "rostris" for " snout ".
Fossil History and Evolution
There are two theories about the origin of the two species of elephant seals, according to which either the northern species is regarded as a descendant of the southern or the southern species is regarded as a descendant of the northern one. According to an older theory, the northern elephant seals originated from a group of southern elephant seals that migrated to the North Pacific during the Pleistocene and became separated from the original population after the warming of the equatorial regions. Alternatively, it is believed that the origin of the elephant seals lies in the more northern tropical areas of the Pacific and from there a group split off and migrated south, where the southern elephant seal emerged. The last view is considered to be more probable and it is assumed that the family group around the elephant seals and the fossil genus Callophoca originated in the Miocene in the area of today's Caribbean and the ancestors of the elephant seals through the not yet closed gap between the north - and South America reached the Pacific in the early Pliocene . As a result of the cooling of the equatorial areas in the Pleistocene, the populations of the later northern and southern elephant seals separated and were genetically isolated accordingly. The oldest fossil finds of the northern elephant seal come from the late Pleistocene from southern California, fossil finds of the southern species are known from South Africa and the north of Chile .
Threat and protection
The northern elephant seal was originally distributed without gaps along the west coast of North America from Alaska to Baja California and was historically hunted by natives on the coast of Washington and in the Juan de Fuca Strait in British Columbia down to California. In the 19th century, the animals were hunted on a massive scale by whale and seal hunters because they wanted to use their oil commercially. Thousands of elephant seals fell victim to the hunters every year, so that the northern species of elephant seals was ultimately believed to be extinct around 1880. A single tiny herd of less than a hundred animals had survived on the Mexican island of Guadalupe and was discovered around 1892. After the rediscovery, the species was placed under protection and was able to spread again. Around 1900 the population was estimated to be a few hundred animals, the populations spreading northwards. In the 1950s, elephant seals first went ashore to mate on the California Channel Islands of San Miguel, San Nicolas and Santa Barbara. Around 1990 the population was estimated at 127,000 animals. The species is now back on numerous offshore islands northwards to the Farallon Islands , and outside of the mating season even to Vancouver Island .
On Highway 1 between Los Angeles and San Francisco, the elephant seals are again a tourist attraction in certain places and larger colonies can be observed from special vantage points at Point Piedras Blancas . The colony that settled there in 1990 has since expanded to more than 15,000 animals (2010). The total population increases annually by about 15%, so that the northern elephant seal is no longer considered to be seriously endangered. However, the near-extinction in the meantime has led to an extreme genetic uniformity of all individuals ( genetic bottleneck ) which, if the conditions change, could be disadvantageous for the species in terms of susceptibility to disease and deteriorating environmental conditions. Further potential dangers for elephant seals as top predators in the open sea are environmental pollution to which the animals are exposed. Following some studies, the animals accumulate, for example, heavy metals such as mercury or toxins such as polychlorinated biphenyls (PCBs) during their migration in the sea, whereby the amount and concentration can vary greatly from one location to another. In addition, there is global warming , due to which the temperatures of the waters and the air in the area of the southernmost colonies in the Baja California area have increased in the last few decades. Since the distribution areas of the northern elephant seals are mainly influenced by temperatures and the animals avoid warm and tropical waters, after an increase up to around 1990, significant declines in populations and births were recorded on Guadelupe and the Islas San Benito .
Due to the large distribution area and the current lack of serious threats to the entire population, the International Union for Conservation of Nature and Natural Resources (IUCN) classifies the species as "Least Concern". This classification is justified by the large and growing population of the animals and the assumption that this trend will continue. In the United States, elephant seals are protected by the Marine Mammal Protection Act and in Mexico they are protected from direct hunting by the Norma Oficial Mexicana (NOM-059-ECOL-2001). In addition, the mating beaches and the molting beaches are classified as protected areas.
Individual evidence
- ↑ a b c d e f g h i j k l m n o Brent S. Stewart, Harriet S. Huber: Mirounga angustirostris . In: Mammalian Species . tape 449 , 1993, pp. 1–10 , doi : 10.2307 / 3504174 ( full text (PDF file; 1.27 MB)). Full text ( Memento from March 18, 2014 in the Internet Archive )
- ↑ a b c d e f g h i j k l m Mirounga angustirostris in the Red List of Threatened Species of the IUCN 2017.3. Posted by: L. Hückstädt, 2015. Retrieved on May 19, 2018.
- ↑ a b c d e f g h i j k l m n o Brent S. Stewart: "Northern Elephant Seal - Miounga angustirostris." In: In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; Pp. 170-171. ISBN 978-84-96553-93-4 .
- ↑ Simona Sanvito, Alejandro Dueñes Meza, Yolanda Schramm, Pedro Cruz Hernández, Yareli Esquer Garrigos, Filippo Galimberti: Isolation and cross-species amplification of novel microsatellite loci in a charismatic marine mammal species, the northern elephant seal (Mirounga angustirostris). Conservation Genetics Resources 5 (1), March 2013; Pp. 93-96.
- ^ A. Abadia-Cardoso, NB Freimer, K. Deiner, JC Garza: Molecular Population Genetics of the Northern Elephant Seal Mirounga angustirostris. Journal of Heredity 08 (6), pp. 618-627. doi : 10.1093 / jhered / esx053 .
- ↑ a b c d e f g h i Karen Warburton: Mirounga angustirostris in the Animal Diversity Net. Retrieved April 9, 2012.
- ↑ a b c B. J. Le Boeuf, DE Crocker, DP Costa, SB Blackwell, PM Webb, DS Houser: Foraging ecology of Northern Elephant Seals. Ecological Monographs 70 (3), February 2000; Pp. 353-382. doi : 10.1890 / 0012-9615 (2000) 070 [0353: FEONES] 2.0.CO; 2
- ^ A b Y. Mitani, RD Andrews, K. Sato, A. Kato, Y. Naito, DP Costa: Three-dimensional resting behavior of northern elephant seals: drifting like a falling leaf. Biology Letters 6 (2), 2010; Pp. 163-166. doi : 10.1098 / rsbl.2009.0719 .
- ↑ a b Jeff W Higdon, Olaf RP Bininda-Emonds, Robin MD Beck, Steven H. Ferguson: Phylogeny and divergence of the pinnipeds (Carnivora: Mammalia) assessed using a multigene dataset. BMC Evolutionary Biology 7, 2007. doi : 10.1186 / 1471-2148-7-216 .
- ↑ Olaf RP Bininda-Emonds, AP Russell: A morphological perspective on the phylogenetic relationships of the extant phocid seals (Mammalia: Carnivora: Phocidae) . In: Bonn Zoological Monographs 1996, Vol. 41.
- ↑ JL Davies: The Pinnipedia: An Essay in Zoogeography. Geographical Review 48 (4), October 1958; Pp. 474-493. doi : 10.2307 / 211670
- Jump up ↑ Ana M. Valenzuela-Toro, Carolina S. Gutstein, Mario E. Suárez, Rodrigo Otero & Nicholas D. Pyenson: Elephant seal (Mirounga sp.) From the Pleistocene of the Antofagasta Region, northern Chile. Journal of Vertebrate Paleontology 35 (3), April 2015; e918883. doi : 10.1080 / 02724634.2014.918883 .
- ↑ Will Houston: Photos: Over 200 elephant seals take over, closing Marin beach - again , in: The Mercury News of May 24, 2019, last accessed on December 16, 2019.
- ↑ SH Peterson, JT Ackerman, DP Costa: Marine foraging ecology influences mercury bioaccumulation in deep-diving northern elephant seals. Proceedings of the Royal Society B: Biological Sciences 282 (1810), 2015; P. doi : 10.1098 / rspb.2015.0710 .
- ↑ Sarah H. Peterson, Jason L. Hassrick, Anne Lafontaine, Jean-Pierre Thomé, Daniel E. Crocker, Cathy Debier, Daniel P. Costa: . PLoS ONE 9 (4), April 22, 2014: e96191. doi : 10.1371 / journal.pone.0096191 .
- ↑ María C. García-Aguilar, Cuauhtémoc Turrent, Fernando R. Elorriaga-Verplancken, Alejandro Arias-Del-Razo, Yolanda Schramm: Climate change and the northern elephant seal (Mirounga angustirostris) population in Baja California, Mexico. PLoS ONE 13 (2) February 15, 2018; e0193211. doi : 10.1371 / journal.pone.0193211 .
literature
- Brent S. Stewart: "Northern Elephant Seal - Miounga angustirostris." In: In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; Pp. 170-171. ISBN 978-84-96553-93-4 .
- Brent S. Stewart, Harriet S. Huber: Mirounga angustirostris . In: Mammalian Species . tape 449 , 1993, pp. 1–10 ( full text (PDF file; 1.27 MB)).
- Ronald M. Nowak: Walker's Mammals of the World . Johns Hopkins University Press, 1999, ISBN 0-8018-5789-9
- Judith E. King : Seals of the World . Cornell University Press, 1983, ISBN 0-8014-1568-3
Web links
- Mirounga angustirostris inthe IUCN Red List of Threatened Species 2017.3. Posted by: L. Hückstädt, 2015. Retrieved on May 19, 2018.
- Karen Warburton: Mirounga angustirostris on the Animal Diversity Net.