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Northern elephant seal
The northern elephant seal (Mirounga angustirostris) is one of two species of elephant seal (the other is the southern elephant seal). It is a member of the family Phocidae (true seals). Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great. Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.
The huge male northern elephant seal typically weighs 1,500–2,300 kg (3,300–5,100 lb) and measures 4–5 m (13–16 ft), although some males can weigh up to 3,700 kg (8,200 lb). Females are much smaller and can range from 400 to 900 kg (880 to 1,980 lb) in weight, or roughly a third of the male's bulk, and measure from 2.5 to 3.6 m (8.2 to 11.8 ft). The bull southern elephant seals are, on average, larger than those in the northern species, but the females in both are around the same size, indicating the even higher level of sexual dimorphism in the southern species. Northern elephant seals typically live for around nine years.
Pups are born with dark, almost black fur that they shed after weaning to turn silvery grey. As they develop, both juveniles and adults go through a molting period in which their initially black fur is replaced with a coat that ranges from silver to deep grey, finally fading to tan. Adult males' necks and chests are furless and have a speckled pattern of pink, white, and light brown. This thicker, calloused skin on the neck builds a protective shield in preparation for fights they participate in during the mating season.
The eyes are large, round, and black. The width of the eyes and a high concentration of low-light pigments suggest sight plays an important role in the capture of prey. Like all seals, elephant seals have atrophied hind limbs whose underdeveloped ends form the tail and tail fin. Each of the "feet" can deploy five long, webbed fingers. This agile, dual palm is used to propel water. The pectoral fins are used little while swimming.[citation needed] While their hind limbs are unfit for locomotion on land, elephant seals use their fins as support to propel their bodies. They are able to propel themselves quickly — as fast as 8 kilometres per hour (4.3 kn; 5.0 mph) — in this way for short-distance travel, to return to water, catch up with a female or chase an intruder.[citation needed]
Like other seals, elephant seals' bloodstreams are adapted to the cold in which a mixture of small veins surrounds arteries capturing heat from them. This structure is present in extremities such as the hindlimbs.[citation needed]
A unique characteristic of the northern elephant seal is that it has developed the ability to store oxygenated red blood cells (RBC) within its spleen. In a 2004 study researchers used MRI to observe physiological changes of the spleens of five seal pups during simulated dives. By three minutes, the spleens on average contracted to a fifth of their original size, indicating a dive-related sympathetic contraction of the spleen. Also, a delay was observed between contraction of the spleen and increased hematocrit within the circulating blood, and attributed to the hepatic sinus. This fluid-filled structure is initially expanded due to the rush of RBC from the spleen and slowly releases the red blood cells into the circulatory system via a muscular vena caval sphincter found on the cranial aspect of the diaphragm. This ability to slowly introduce RBC into the blood stream is likely to prevent any harmful effects caused by a rapid increase in hematocrit.
The northern elephant seal lives in the eastern Pacific Ocean. They spend most of their time at sea, and usually only come to land to give birth, breed, and molt. These activities occur at rookeries that are located on offshore islands or remote mainland beaches. The majority of these rookeries are in California and northern Baja California, ranging from Point Reyes National Seashore, California to Isla Natividad, Mexico. Significant breeding colonies exist at Channel Islands, Año Nuevo State Reserve, Piedras Blancas Light, and the Farallon Islands in the US, and Isla Guadalupe, Isla Benito del Este and Isla Cedros in Mexico. In recent decades the breeding range has extended northwards. In 1976 the first pup was found on Point Reyes and a breeding colony established there in 1981. Since the mid-1990s some breeding has been observed at Castle Rock in Northern California and Shell Island off Oregon, and in January 2009 the first elephant seal births were recorded in British Columbia at Race Rocks. The California breeding population is now demographically isolated from the population in Baja California.
Northern elephant seals exhibit extreme sexual dimorphism in their feeding behaviours. When the males leave their rookeries, they migrate northwards to their feeding grounds along the continental shelf from Washington to the western Aleutians in Alaska. The males mostly feed on benthic organisms on the ocean floor. When the females leave their rookeries, they head north or west into open ocean, and forage across a large area in the northeastern Pacific. They have been recorded as far west as Hawaii. Female elephant seals feed mainly on pelagic organisms in the water column.
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Northern elephant seal
The northern elephant seal (Mirounga angustirostris) is one of two species of elephant seal (the other is the southern elephant seal). It is a member of the family Phocidae (true seals). Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. Sexual dimorphism in size is great. Correspondingly, the mating system is highly polygynous; a successful male is able to impregnate up to 50 females in one season.
The huge male northern elephant seal typically weighs 1,500–2,300 kg (3,300–5,100 lb) and measures 4–5 m (13–16 ft), although some males can weigh up to 3,700 kg (8,200 lb). Females are much smaller and can range from 400 to 900 kg (880 to 1,980 lb) in weight, or roughly a third of the male's bulk, and measure from 2.5 to 3.6 m (8.2 to 11.8 ft). The bull southern elephant seals are, on average, larger than those in the northern species, but the females in both are around the same size, indicating the even higher level of sexual dimorphism in the southern species. Northern elephant seals typically live for around nine years.
Pups are born with dark, almost black fur that they shed after weaning to turn silvery grey. As they develop, both juveniles and adults go through a molting period in which their initially black fur is replaced with a coat that ranges from silver to deep grey, finally fading to tan. Adult males' necks and chests are furless and have a speckled pattern of pink, white, and light brown. This thicker, calloused skin on the neck builds a protective shield in preparation for fights they participate in during the mating season.
The eyes are large, round, and black. The width of the eyes and a high concentration of low-light pigments suggest sight plays an important role in the capture of prey. Like all seals, elephant seals have atrophied hind limbs whose underdeveloped ends form the tail and tail fin. Each of the "feet" can deploy five long, webbed fingers. This agile, dual palm is used to propel water. The pectoral fins are used little while swimming.[citation needed] While their hind limbs are unfit for locomotion on land, elephant seals use their fins as support to propel their bodies. They are able to propel themselves quickly — as fast as 8 kilometres per hour (4.3 kn; 5.0 mph) — in this way for short-distance travel, to return to water, catch up with a female or chase an intruder.[citation needed]
Like other seals, elephant seals' bloodstreams are adapted to the cold in which a mixture of small veins surrounds arteries capturing heat from them. This structure is present in extremities such as the hindlimbs.[citation needed]
A unique characteristic of the northern elephant seal is that it has developed the ability to store oxygenated red blood cells (RBC) within its spleen. In a 2004 study researchers used MRI to observe physiological changes of the spleens of five seal pups during simulated dives. By three minutes, the spleens on average contracted to a fifth of their original size, indicating a dive-related sympathetic contraction of the spleen. Also, a delay was observed between contraction of the spleen and increased hematocrit within the circulating blood, and attributed to the hepatic sinus. This fluid-filled structure is initially expanded due to the rush of RBC from the spleen and slowly releases the red blood cells into the circulatory system via a muscular vena caval sphincter found on the cranial aspect of the diaphragm. This ability to slowly introduce RBC into the blood stream is likely to prevent any harmful effects caused by a rapid increase in hematocrit.
The northern elephant seal lives in the eastern Pacific Ocean. They spend most of their time at sea, and usually only come to land to give birth, breed, and molt. These activities occur at rookeries that are located on offshore islands or remote mainland beaches. The majority of these rookeries are in California and northern Baja California, ranging from Point Reyes National Seashore, California to Isla Natividad, Mexico. Significant breeding colonies exist at Channel Islands, Año Nuevo State Reserve, Piedras Blancas Light, and the Farallon Islands in the US, and Isla Guadalupe, Isla Benito del Este and Isla Cedros in Mexico. In recent decades the breeding range has extended northwards. In 1976 the first pup was found on Point Reyes and a breeding colony established there in 1981. Since the mid-1990s some breeding has been observed at Castle Rock in Northern California and Shell Island off Oregon, and in January 2009 the first elephant seal births were recorded in British Columbia at Race Rocks. The California breeding population is now demographically isolated from the population in Baja California.
Northern elephant seals exhibit extreme sexual dimorphism in their feeding behaviours. When the males leave their rookeries, they migrate northwards to their feeding grounds along the continental shelf from Washington to the western Aleutians in Alaska. The males mostly feed on benthic organisms on the ocean floor. When the females leave their rookeries, they head north or west into open ocean, and forage across a large area in the northeastern Pacific. They have been recorded as far west as Hawaii. Female elephant seals feed mainly on pelagic organisms in the water column.
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