Sea Lions
The Family Otariidae includes the fur seals and sea lions and are called otariids collectively. Their "cousins", the Phocids, are known as “true” seals and are distinguished from fur seals and sea lions primarily by their lack of external ears.
The name otariid comes from the Greek otarion, which means "little ear" and refers to the small external ear flaps found on all fur seals and sea lions. In addition to the presence of external ear flaps, otariids also have larger foreflippers and pectoral muscles than the phocids along with the ability to turn their hind limbs forward and “walk”, albeit clumsily, on their foreflippers and tails, which helps them maneuver better on land where they spend most of their time. The tails can be rotated, which helps support the body and aid in mobility on land. Otariids also have a small but distinct tail.
Unlike the phocids, otariids are generally less adapted to an aquatic lifestyle. They breed on land and haulout more frequently than true seals. Though the phocids are able to swim deeper and for longer periods of time, the otariids can attain higher bursts of speed and are more agile in the water. Though their bodies are slender and elongate and like the phocids, otariids tend to use their longer, paddle-like flippers more than their bodies for swimming, and have larger pectoral muscles than the true seals.
Otariids are further distinguished from phocids by a more dog-like head and they also have sharp, well-developed canine teeth. The post-canines are simple and conical in shape. Sea lions, when fully grown, range from 30 kg and 1.2 m long (Galápagos fur seals, the smallest of all pinnipeds) to more than 1,000 kg and over 3 m long in male Steller sea lions (male southern elephant seals, by comparison, reach 4,000 kg and over 6 m in length, the largest of all pinnipeds). Mature male otariids are larger than females, typically weighing two to six times more with proportionately larger heads, necks, and chests making them the most distinctively sexually dimorphic of all mammals.
All otariids have fur; fur seals can be distinguished from sea lions by the presence of dense underfur consisting of about 30 secondary hairs to each primary hair.
Taxonomy
In the past, otariids were subdivided into the fur seal (Arctocephalinae) and sea lion (Otariinae) subfamilies due to fur seals having a thick layer of underfur which sea lions don't have. The fur seals comprise two genera: Callorhinus in the North Pacific with the Northern fur seal, Callorhinus ursinus, and eight species in the southern hemisphere genus Arctocephalus. Sea lions have seven species under five genera. More recently, genetic evidence suggests that Callorhinus ursinus is closely related to several sea lion species. The Japanese sea lion was then determined to be a separate species, Zalophus japonicus, rather than a subspecies of the California sea lion, Zalophus californius. Now the Otariidae family is organized into seven genera with 16 species including two subspecies.
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Carnivora
Suborder Pinnipedia
Family Otariidae (eared seals, sea lions) | +ITIS
- Genus Arctocephalus (southern fur seals)
- Antarctic fur seal, Arctocephalus gazella
- Galápagos fur seal, Arctocephalus galapagoensis
- Guadalupe fur seal, Arctocephalus townsendi
- Juan Fernandez fur seal, Arctocephalus philippii
- New Zealand fur seal, Arctocephalus forsteri
- Arctocephalus pusillus
- South American fur seal, Arctocephalus australis
- Subantarctic fur seal, Arctocephalus tropicalis
- Genus Callorhinus (northern fur seals)
- Genus Eumetopias (northern sea lions)
- Genus Neophoca
- Genus Otaria
- Genus Phocarctos
- Genus Zalophus (California sea lions)
Family Phocidae (true seals)
Family Odobenidae (walrus)
Evolution
Like the phocids, otаriids are descended from a common ancestor that first gave rise to bears (Ursidae) and then dogs (Canidae) and racoons (Procyonidae) approximately 23 million years ago in the early Miocene. Otariids, as we know them today, are thought to have evolved in the late Miocene (about 7 million years ago) in the North Pacific or Arctic region and then diversified into the southern hemisphere. Northern fur seals (Callorhinus) have the oldest fossil record of any existing otariids followed by Zalophus and Arctocephalus and the late comer, Eumetopias or Steller sea lion.
Adapting to the Sea
Sea lions are remarkably adapted to the ocean.
>>> THE BELOW IS FOR SEALS NOT SEA LIONS - REPLACE ENTIRELY
They have powerful, sleek, tapered bodies that enable them to glide through the water. Their heads connect directly to their bodies with loosely interlocked vertebrae that make them strong and flexible to swim through waves and navigate ice and rocky shores. They have developed adaptations to reduce their energy use and increase availability of oxygen while diving. They are wrapped in warm blubber to insulate them from polar waters. Phocids rely on blubber more than otariids do because they spend much more time in the water. Sea lion nostrils close underwater and shut very tightly as the water pressure increases. They can dive for very long periods—up to two hours for elephant seals. True seals can also dive to very deep depths, southern elephant seals have been observed diving up to 1,200 m, Weddell and hooded seals up to 1,400 m. Seals have two extra pairs of ribs to allow room for their large lungs. They don't store air in the lungs for diving though; they hyperventilate before diving to collect and store the oxygen in their blood and muscles, expelling extra air before diving. During deep dives, the pressure of other organs collapses the seal's diaphragm against its lungs and forces out any extra air. Seals also have more blood to carry oxygen than other similarly sized mammals.
They also reduce their heart rate to about 15 beats per minute during long dives. Vital organs such as the heart and lungs continue to receive oxygen while the peripheral body parts go without. If a seal runs out of oxygen, then glucose is converted to lactic acid through a process called glycolysis. Weddells and other true seals even have extra-big spleens to store red blood cells that are released later during a dive.
Seals have flat corneas and pupils that can open wide to let in light while swimming. Unlike other mammals, seal eyes only have rods (sensory cells) that work great in low light. They don't have cones (other sensory cells) needed to detect color. In water, a seal's eye lens sends an image directly to the back of the eyeball. Land mammals use their lens for focusing only. Though seals have retinas like land animals do, they don't have the curved eye surface to refract light and project an image onto the retina at the back of the eyeball. Seals also have long whiskers with many nerve endings that are sensitive to the movement of prey and help them navigate murky waters.
When they return to shore, seals get to relax for about twice the time of their energy-intense dive to allow their heart rate to return to normal and so that they can rid their body of accumulated lactic acid.
Communications and Social Behavior
Communication among otariids is an important factor of their behavior for these highly social animals. They are known to have rich vocal repertoires. The loudest call is known as the “full threat call”, which carries the farthest distance. Because they congregate in large numbers, acoustic signaling through various vocalizations is the most effective form of communication. Vocal communications can vary greatly between individuals. Scientists have studied the acoustic structure of the vocalizations as well as their use in the social function of calls in communication. Otariid barks, squeaks, and yelps are used to communicate between males and females during breeding and between females and their pups. It has been suggested that mother-pup recognition exists through recognized vocalizations. The barks of males can be used to recognize individuals in their herd. Scientists have studied territorial male Australian fur seals and found that they respond more to the calls of strangers than to calls of their neighbors.
World Range & Habitats
Otariids are adapted to a semi-aquatic lifestyle, feeding and migrating in the water but breeding and resting on land. They can be found in subpolar, temperate, and equatorial waters throughout the Pacific and Southern oceans and the southern Indian and Atlantic oceans. They are not found in the North Atlantic which is likely due historical explotation by humans.
Ecology
Otariids feed on fish, squid and krill. Sea lions tend to feed closer to shore in upwelling zones on larger fish while the smaller fur seals tend to take longer, offshore hunting trips catching a larger number of smaller prey species with some females reported to be able to dive to depths of up to 400 m.
Life Histories
All otariids breed on land and are highly social. They aggregate yearly on beaches or rocky shorelines. They are polygynous meaning that males breed with several females and form harems consisting of between 3-40 individuals. Males tend to arrive at breeding sites first to establish their territories through vocal and visual displays and, of course, the occasional brawl though there are no clear hierarchies established in the colonies. The females arrive to give birth from the previous year's breeding season, then prepare to breed again. Implantation is delayed so that the females will be ready to give birth during the following breeding season. The breeding behaviors vary among species. Northern fur seals and South American sea lions tend to herd the females in their harems into their territory. The Steller and New Zealand sea lions control their territories but do not interfere with the movement of the females.
Soon after they arrive, females give birth to pups from the previous year's breeding season, and within a few days, enter estrous. Mating takes place on land. A period of delayed implantation insures that the young will be born in a year, when the breeding herds form again.
Females leave their pups a week after birth to hunt before she begins nursing. The pups fast for the 1-14 days that their mother is gone. The mother returns to nurse for 2-3 days, then leaves again. If food is abundant, then the foraging trips are shorter because the mother can produce more milk. Females nurse for 6-11 months, with the exception of the Galapagos fur seal, which nurses for as long as 3 years.
Endangered Status
A number of otariid species are in jeopardy of extinction. The Steller sea lion is listed as endangered on the IUCN red list. Steller sea lions in the west have been declining rapidly over the past few decades; in 2000 there were only about 45,000 Steller sea lions left in the western population. Though the cause is unknown, it is thought that commercial fishing has decimated the primary prey of this species. Guadalupe fur seals were heavily hunted in the 18th centuries; at one point they were thought to be extinct. Today, this species is listed as vulnerable on the IUCN Red List with current populations estimated at 10,000. Northern fur seals are also listed as vulnerable on the IUCN Red List due to steep declines in recent years in the Pribilof population, which represents 50% of the global population. Strangely, the birth rate is still strong, yet the numbers continue to drop.
References
Feedback?
Something missing or incorrect in the above? Let us know!
Sea Life News :: ScienceDailyAncient seagrass holds secrets of the oldest living organism on Earth
It's big, it's old and it lives under the sea -- and now an international research collaboration has confirmed that an ancient seagrass holds the secrets of the oldest living organism on Earth. Ancient giant Posidonia oceanica reproduces asexually, generating clones of itself. A single organism -- which has been found to span up to 15 kilometers in width and reach more than 6,000 metric tonnes in mass -- may well be more than 100,000 years old.
2011 shark attacks remain steady, deaths highest since 1993
Shark attacks in the US declined in 2011, but worldwide fatalities reached a two-decade high, according to the a new report.
Satellite tracking reveals sea turtle feeding hotspots
Satellite tracking of threatened loggerhead sea turtles has revealed two previously unknown feeding "hotspots" in the Gulf of Mexico that are providing important habitat for at least three separate populations of the turtles.
Global extinction: Gradual doom is just as bad as abrupt
Around 250 million years ago, most life on Earth was wiped out in an extinction known as the "Great Dying." Geologists have learned that the end came slowly from thousands of centuries of volcanic activity.
Scientists coax shy microorganisms to stand out in a crowd
Scientists have advanced a method that allowed them to single out a marine microorganism and map its genome even though the organism made up less than 10 percent of a water sample teeming with many millions of individuals from dozens of identifiable groups of microbes.
Heat and cold damage corals in their own ways
Around the world coral reefs are facing threats brought by climate change and dramatic shifts in sea temperatures. While warming has been the primary focus for scientists and ocean policy managers, cold can also cause significant damage. Scientists have shown that cool temperatures can inflict more damage in the short term, but heat is more destructive in the long run.
Are nuisance jellyfish really taking over the world's oceans?
Evidence is lacking that populations of jellyfish and similar gelatinous plankton are surging in numbers globally and will likely dominate the seas in coming decades. Rather, increasing scientific and media interest as well as the lack of good baseline data seem to explain the widespread perception of an increase.
Global experts question claims about jellyfish populations
Blooms, or proliferation, of jellyfish have shown a substantial, visible impact on coastal populations -- clogged nets for fishermen, stinging waters for tourists, even choked intake lines for power plants -- and recent media reports have created a perception that the world's oceans are experiencing increases in jellyfish due to human activities such as global warming and overharvesting of fish. Now, a new study questions claims that jellyfish are increasing worldwide and suggests claims are not supported with any hard evidence or scientific analyses to date.
Are jellyfish increasing in world's oceans?
A global study has questioned claims that jellyfish are increasing worldwide. Blooms, or proliferation, of jellyfish have shown a substantial, visible impact on coastal populations -- clogged nets for fishermen, stinging waters for tourists, even choked intake lines for power plants -- and recent media reports have created a perception that the world's oceans are experiencing increases in jellyfish due to human activities such as global warming and overharvesting of fish. Now, a new global and collaborative study questions claims that jellyfish are increasing worldwide and suggests claims are not supported with any hard evidence or scientific analyses to date.
Southern Indian ocean humpback whales found singing different tunes
Humpback whales on both sides of the southern Indian Ocean are singing different tunes, unusual since humpbacks in the same ocean basin usually all sing very similar songs.
Mammals shrink at faster rates than they grow: Research helps explain large-scale size changes and recovery from mass extinctions
It took about 10 million generations for terrestrial mammals to hit their maximum mass: that's about the size of a cat evolving into the size of an elephant. Sea mammals, such as whales took about half the number of generations to hit their maximum.
What do killer whales eat in the Arctic?
Killer whales are the top marine predator. The increase in hunting territories available to killer whales in the Arctic due to climate change and melting sea ice could seriously affect the marine ecosystem balance. New research has combined scientific observations with Canadian Inuit traditional knowledge to determine killer whale behavior and diet in the Arctic.
Detecting detrimental change in coral reefs
Over dinner on R.V. Calypso while anchored on the lee side of Glover's Reef in Belize, Jacques Cousteau told Phil Dustan that he suspected humans were having a negative impact on coral reefs. Dustan -- a young ocean ecologist who had worked in the lush coral reefs of the Caribbean and Sinai Peninsula -- found this difficult to believe. It was December 1974. But Cousteau was right. During the following three-plus decades, Dustan, an ocean ecologist and biology professor at the University of Charleston in South Carolina, has witnessed widespread coral reef degradation and bleaching from up close.
Ecologists capture first deep-sea fish noises
Fish biologists conducted one of the first studies of deep-sea fish sounds in more than 50 years, 2,237 feet under the Atlantic. With recording technology more affordable, fish sounds can be studied to test the idea that fish communicate with sound, especially those in the dark of the deep ocean.
Life beyond Earth? Underwater caves in Bahamas could give clues
Discoveries made in some underwater caves by researchers in the Bahamas could provide clues about how ocean life formed on Earth millions of years ago, and perhaps give hints of what types of marine life could be found on distant planets and moons.
Viruses con bacteria into working for them
Researchers have discovered that certain photosynthetic ocean bacteria need to beware of viruses bearing gifts. These viruses are really con artists carrying genetic material taken from their previous bacterial hosts that tricks the new host into using its own machinery to activate the genes, a process never before documented in any virus-bacteria relationship. The con occurs when a grifter virus injects its DNA into a bacterium living in a phosphorus-starved region of the ocean.
Microbubbles provide new boost for biofuel production
A solution to the difficult issue of harvesting algae for use as a biofuel has been developed using microbubble technology.
Attack or retreat? Circuit links hunger and pursuit in sea slug brain
If you were a blind, cannibalistic sea slug, living among others just like you, nearly every encounter with another creature would require a simple cost/benefit calculation: Should I eat that -- or flee? In a new study, researchers report that these responses are linked to a simple circuit in the brain of the sea slug Pleurobranchaea.
Where there's a worm there's a whale: First distribution model of marine parasites provides revealing insights
Each year around 20,000 people are infected by nematodes of the genus Anisakis and suffer from illnesses ranging from gastrointestinal diseases to serious allergic reactions as a result. For the first time, parasitologists have gathered data on the occurrence of the parasitic worm and have modeled the worldwide distribution of individual species in the ocean. The resulting maps not only enable statements to be made on the occurrence and migration behavior of certain hosts of the parasites, such as Baleen or toothed whales, but also provide conclusions on the risk of human infection.
Turtles' mating habits protect against effects of climate change
The mating habits of marine turtles may help to protect them against the effects of climate change. The study shows how the mating patterns of a population of endangered green turtles may be helping them deal with the fact that global warming is leading to a disproportionate number of females being born.
Help us continue to share the wonders of the ocean with the world, raise awareness of marine conservation issues and their solutions, and support marine conservation scientists and students involved in the marine life sciences. Join the MarineBio Conservation Society or make a donation today. We would like to sincerely thank all of our members and donors, we simply could not have achieved what we have without you and we look forward to doing even more.
