Sea Mammal Groups
Weasels & Kin
When you think of aquatic mammals, do you think of a whale or an otter? In truth, there are a number of mammals who rely on water for hunting and fishing, as well as those who spend their entire lives in the sea. Although they may look like fish, dolphins and whales are in fact mammals -- they are warm blooded, have very fine hairs on their bodies, and produce milk to feed their young. While they never emerge from the water, however, other sea mammals like seals and sea lions divide their time equally between water and land, using it for both for fishing and for fun.
Whales in captivity which were captured from different oceans often suffer "culture shock" when forced to share an enclosure. Scientists believe that, just like people, whales from different parts of the world speak their own language, so that animals of the same species can't understand each other.
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رد: Sea Mammal Groups
Blue whales were abundant in most oceans around the world until the beginning of the twentieth century. For the first 40 years of that century they were hunted by whalers almost to extinction. Hunting of the species was outlawed by the international community in 1966. A 2002 report estimated there were 5,000 to 12,000 Blue whales worldwide located in at least five groups. More recent research into the Pygmy subspecies suggest this may be an under-estimate. Before whaling the largest population (202,000 to 311,000) was in the Antarctic but now there remain only much smaller (around 2,000) concentrations in each of the North-East Pacific, the Antarctic, and the Indian Ocean. There are two more groups in the North Atlantic and at least two (possibly more) in the Southern Hemisphere.
The long and tapered whale:
The Blue whale has a long tapering body that appears stretched in comparison with the much stockier appearance of other whales. The head is flat and U-shaped and has a very prominent ridge running from the blowhole to the top of the upper lips.
Lots of plates:
The front part of the mouth is thick with baleen plates; around 300 plates (each one meter long) hang from the upper jaw, running half a meter back into the mouth. Between 60 and 90 grooves (called ventral pleats) run along the throat parallel to the body. These pleats assist with evacuating water from the mouth after lunge feeding.
Varying fin shape:
The dorsal fin is small, visible only briefly during the dive sequence. It varies in shape from one individual to another; some only have a barely perceptible lump, whilst other fins are quite prominent and falcate(sickle shaped). It is located around three-quarters of the way along the length of the body.
A spectacular column of water :
When surfacing to breathe, the Blue whale raises its shoulder and blow hole region out of the water to a greater extent than other large whales (such as the Fin or Sei). This can often be a useful clue to identifying a species at sea. Whilst breathing, the whale emits a spectacular vertical single column blow (up to 12 m, typically 9 m) that can be seen from many kilometers on a calm day. Its lung capacity is 5,000 liters.
The flippers are three to four meters long. The upper side is gray with a thin white border. The lower side is white. The head and tail fluke are generally uniformly gray colored whilst the back, and sometimes the flippers, are usually mottled. The degree of mottling varies substantially from individual to individual. Some may have a uniform gray color all over, whilst others demonstrate a considerable variation of dark blues, grays and blacks all tightly mottled.
The largest animal ever!
The Blue whale is believed to be the largest animal ever to have lived on Earth. The largest known dinosaur of the Mesozoic era was the Argentinosaurus, which is estimated to have weighed up to 90 tonnes (100 short tons). There is some uncertainty as to the biggest Blue whale ever found. Most data comes from Blue whales killed in Antarctic waters during the first half of the twentieth century and was collected by whalers not well-versed in standard zoological measurement techniques. The longest whales ever recorded were two females measuring 33.6 m and 33.3 m (110 ft 3 in and 109 ft 3 in) respectively. However, there are some disputes over the reliability of these measurements. The longest whales measured by scientists at the American National Marine Mammal Laboratory (NMML) was 29.9 m long (98 ft) — about the same length as a Boeing 737 airplane or three double-decker buses.
Blue whales feed exclusively on krill. The whales always feed on the highest concentration of krill that they can find. This means that they typically feed at depth (more than 100 m) during the daytime, and only surface feed at night. Dive times are typically ten minutes when feeding. Diving for twenty minutes is quite common. The longest recorded is thirty-six minutes (Sears 1998). The whale feeds by lunging forward at groups of krills, taking the animals and a large quantity of water into the mouth at once. The water is then squeezed out through the baleen plates by pressing the ventral pouch and tongue up against the water. Once the mouth is clear of water, the remaining krill, unable to pass through the plates, are swallowed. According to Ted Dewan's Inside the Whales and Other Animals, as well as krill, the Blue whale filters small fish and squid. It may even swallow something else that was also feeding on the krill.
The loudest animal we can't hear:
The Blue whale is the loudest animal in the world. Estimates suggest that source level of sounds made by Blue whales are between 155 and 188 decibels when measured at a reference pressure of one micropascal at one meter. By comparison, a pneumatic drill is about 100 dB. A human, however, would likely not perceive the Blue whales as the loudest of all animals. All Blue whale groups make calls at a fundamental frequency of between 10 and 40 Hz, and the lowest frequency sound a human can typically perceive is 20 Hz. Blue whale calls last between ten and thirty seconds. Additionally Blue whales off the coast of Sri Lanka have been recorded repeatedly making "songs" of four notes duration lasting about two minutes each, reminiscent of the well-known Humpback whale songs. Researchers believe that as this phenomenon has not been seen in any other populations, it may be unique to the B. m. brevicauda (Pygmy) subspecies.
Mating starts in late autumn, and continues to the end of winter. Little is known about mating behavior or even breeding grounds. Females typically give birth at the start of the winter once every two to three years after a gestation period of ten to twelve months. The calf weighs about two and a half tonnes and is around 7 m in length. Weaning takes place after about six months, by which time the calf has doubled in length. Sexual maturity is typically reached at eight to ten years by which time males are at least 20 m long (or more in the southern hemisphere). Females are larger still, reaching sexual maturity around 21 m or around the age of five.
Eighty year olds?
Scientists estimate that Blue whales can live for at least eighty years; however, since individual records do not date back into the whaling era, this will not be known with certainty for many years yet. The longest recorded study of a single individual is thirty-four years, in the north-east Pacific (reported in Sears, 1998). The whales' only natural predator is the Orca. Some reports claim that as many as 25% of mature Blue whales have scars resulting from Orca attacks. The rate of mortality due to such attacks is unknown.
Beaching themselves to breathe:
Blue whales strandings are extremely uncommon and, because of the species' social structure, mass strandings are unheard of. However, when strandings do occur they can become quite a public event. In 1920, a Blue whale washed up near Bragar on the Isle of Lewis in the Outer Hebrides of Scotland. It had been shot in the head by whalers, but the harpoon had failed to explode. As with other mammals, the fundamental instinct of the whales was to try to carry on breathing at all costs, even though this meant beaching to prevent itself from drowning. Two of the whales's bones were erected just off a main road on Lewis, and remain a tourist attraction.
Dolphins are aquatic mammals related to whales and porpoises, famous for their intelligence, apparent compassion, and joy. The name is from Ancient Greek δελφίς (delphis) meaning "with a womb", viz. "a 'fish' with a womb". A group of dolphins can be called a "school" or a "pod".
There are almost 40 species of dolphin in 17 genera. They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about 10 million years ago, during the Miocene period.
They vary in size from 1.2 m (4 ft) and 40 kg (88 lb) (Maui's dolphin), up to 9.5 m (30 ft) and 10 tonnes (the Orca). However, the average length for most North American species is 13.89 feet in length. Most species weigh about 50 to 200 kg (110 to 440 lb).
The smartest animal? Dolphins are widely believed to be among the most intelligent of all animals, though it is hard to say just how intelligent dolphins are, as straightforward comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of doing experimental work with large marine animals means that some tests that could meaningfully be done still have not been carried out, or have been carried out with inadequate sample size and methodology.
Leaping acrobats and mischievous pranksters:
Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the Spinner dolphin). Scientists are not quite certain about the purpose of this behavior, but it may be to locate schools of fish by looking at above water signs, like feeding birds. They could also be communicating to other dolphins to join a hunt, attempting to dislodge parasites, or simply doing it for fun. Play is a very important part of dolphins' lives and they can often be observed playing with seaweed or play fighting with other dolphins. They have even been seen harassing other creatures, like seabirds and turtles. Dolphins also seem to enjoy riding waves and are frequently seen 'surfing' coastal swells and the bow waves of boats.
Good luck dolphins:
They are also famous for their willingness to occasionally approach humans and playfully interact with them in the water. In return, in some cultures like in Ancient Greece they were treated with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There are many stories of dolphins protecting shipwrecked sailors against sharks by swimming circles around the swimmers. A school of dolphins is also said to have pushed a fishing boat that was returning to shore back out to sea after sensing the underwater disturbances generated by the 2004 Asian Tsunami.
Strong bonds in social pods :
Dolphins are social animals, living in pods (also called "schools") of up to a dozen animals. In places with a high abundance of food, schools can join temporarily, forming an aggregation called a superpod; such groupings may exceed 1000 dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in schools is not rigid; interchange is common. However, the animals can establish strong bonds between each other. This leads to them staying with injured or ill fellows for support.
Favorites with humans:
Because of their high capacity for learning, dolphins have been employed by humans for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Such places may sometimes also provide an opportunity for humans to interact very closely with Dolphins. Dolphin/Human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled children.
Ground control to major dolphin:
The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped persons. Such military dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained to kill Vietnamese Skin Divers. Reports of cooperative human-dolphin fisheries date back to Pliny. A modern human-dolphin fishery was reported in Laguna, Santa Catarina, Brazil in 1990.
In May 2005, researchers in Australia discovered a cultural aspect of dolphin behavior: Some dolphins (Tursiops aduncus) teach their offspring to use tools. The animals break off sponges and carry them over their snouts, thus protecting he delicate body part from dangerous creatures (like stonefish with venomous spines) during their hunt for fish on the seabed, and also dislodging fish they can snap up. This knowledge of how to use a tool is mostly transferred from mothers to daughters in dolphins, unlike simian primates, where the knowledge is generally passed onto all the offspring, irrespective of sex. The technology to use sponges as snout protection is not genetically inherited but a taught cultural behavior
Superior vision and hearing, but no smelling:
Most dolphins have acute eyesight, both in and out of the water, and their sense of hearing is superior to that of humans. Though they have a small ear opening on each side of their head, it is believed that hearing underwater is also if not exclusively done with the lower jaw which conducts the sound vibrations to the middle ear via a fat filled cavity in the lower jaw bone. Hearing is also used for echolocation, which seems to be an ability all dolphins have. The dolphin's sense of touch is also well-developed. However, dolphins lack an olfactory nerve and thus have no sense of smell, but they can taste and do show preferences for certain kinds of fish. Since dolphins spend most of their time below the surface in the wild, just tasting the water could act in a manner analogous to a sense of smell.
Dolphins are predators, chasing their prey at high speed. The dentition is adapted to the animals they hunt: Species with long beaks and many teeth forage on fish, whereas short beaks and lesser tooth count are linked to catching squid. Some dolphins may take crustaceans. Usually, the prey is swallowed whole. The larger species, especially the orca, are capable of eating marine mammals, even large whales. There are no known reports of cannibalism amongst dolphins.
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رد: Sea Mammal Groups
The Humpback whale (Megaptera novaeangliae) is a mammal which belongs to the Baleen whale suborder.It is well known for its breaching (leaping out of the water), its unusually long front fins, and its complex whale song. The Humpback whale lives in oceans and seas around the world, and is regularly sought out by whale-watchers.
It is a large whale: an adult usually ranges between 12–16 m (40–50 ft) long and weighs approximately 36,000 kilograms (79,000 pounds), or 36 tonnes (40 tons).
Feeding in the summer, living off fat in winter:
The species feeds only in summer and lives off fat reserves during winter. It is an energetic feeder, taking krill and small schooling fish, such as herring, capelin and sand lance. It will hunt fish by direct attack or by stunning them by hitting the water with its flippers or flukes.
Humpbacks often 'breach': they leap out of the water with enough upward force that nearly two-thirds of the body comes out of the water, and then comes back to the water again with an enromous splash. Sometimes a twist is involved in the jump, a sideways motion or many other impressive acrobative feats. They have also been seen rolling in the water, slapping the water with their flippers and fluke, butting into other whales and also lifiting themselves straight up out of the water. This often makes whale-watching an extremely exciting event!
Humpback whales are preyed upon by Orcas. The result of these attacks is generally nothing more serious than some scarring of the skin. However, it is likely that young calves are sometimes killed.
Blowing bubbles for a big gulp:
Its most inventive feeding technique is called bubble net fishing. A group of whales swims rapidly in wide circles around and under a school of fish, blowing air through their blowholes. The bubbles form a visual barrier that serves to confine the school within an ever-tighter area. The whales then suddenly swim upwards and through the bubble net, mouths agape, swallowing thousands of fish in one gulp. This technique can involve a ring of bubbles up to 30 m (100 ft) in diameter and the cooperation of a dozen animals at once. It is perhaps the most spectacular act of cooperation among marine mammals.
Alongside its aerial acrobatics, the Humpback whale is well known for its long and complex "song". As cetaceans have no vocal chords, whales generate their songs by forcing air through their massive nasal cavities. Humpbacks repeat patterns of low notes that vary in amplitude and frequency in consistent patterns over a period of hours or even days. Scientists are still unsure what the whalesong is meant to communicate. Only male Humpbacks sing, so it was at first assumed that the songs were solely for courting. While the primary purpose of whalesong may be to attract females, it's almost certain that whalesong serves myriad purposes. Also interesting is the fact that a whale's unique song slowly evolves over a period of years —never returning to the same sequence of notes even after decades.
Curiousity used to mean big trouble:
Humpback whales are generally curious about objects in their environment. They will often approach and circle boats. Whilst this inquisitiveness was akin to suicide when the vessel was a whaling ship, it has become an attraction of whale watching tourism in many locations around the world since the 1990s.
Curiousity works for whale-watching though:
Whale-watching locations include the Pacific coast off Washington, Vancouver, Hawaii and Alaska, the Bay of Biscay to the west of France, Byron Bay north of Sydney, the coasts of New England and Newfoundland, the northern St. Lawrence River and the Snaefellsnes peninsula in the west of Iceland. The species is popular because it breaches regularly and spectacularly, and displays a range of other social behaviors.
As with other cetacean species, however, a mother whale will generally be extremely protective of her infant, and will seek to place herself between any boat and the calf before moving quickly away from the vessel. Whale-watching operators are asked to avoid stressing the mother unduly.
The first recorded Humpback kill was made in 1608 off Nantucket. Opportunistic killing of the species is likely to have occurred long before then, and certainly continued with increasing pace in the following centuries. By the eighteenth century, the commercial value of Humpback Whales had been realized, and they became a common prey of whalers for many years.
Explosive harpoons were bad news to friendly whales: By the 19th century, many nations (in particular, the United States), were hunting the creature heavily in the Atlantic Ocean — and to a lesser extent in the Indian and Pacific Oceans. However, it was the introduction of the explosive harpoon in the late nineteenth century that allowed whalers to accelerate their take. This, coupled with the opening-up of the Antarctic seas in 1904, led to a sharp decline in whale numbers amongst all populations.
90% gone is a terrible crime :
It is estimated that during the 20th century at least 200,000 Humpbacks were taken, reducing the global population by over 90%. To prevent species extinction, a general moratorium on the hunting of Humpbacks was introduced in 1966 and is still in force today. In his book Humpback Whales (1996), Phil Clapham, a scientist at the Smithsonian Institute, says "this wanton destruction of some of the earth's most magnificent creatures [is] one of the greatest of our many environmental crimes".
Stopping barely in time:
By the time the International Whaling Commission members agreed on a moratorium on Humpback hunting in 1966, the whales had become sufficiently scarce as not to be worthwhile hunting commercially. At this time, 250,000 were recorded killed. However, the true toll is likely to be significantly higher. It is now known that the Soviet Union was deliberately under-recording its kills; the total Soviet Humpback kill was reported at 2,710 whereas the true number is now believed to be 48,000.
Starting in 2007 Japan is planning to kill 50 Humpback Whales per year under its JARPA-II research program.
Manatees inhabit the shallow, marshy coastal areas of North, Central, and South America, and the Caribbean Sea. They spend half of their day sleeping in the water, surfacing for air every 20 minutes.
Manatees (family Trichechidae, genus Trichechus) are large aquatic mammals sometimes known as sea cows. The Trichechidae differ from the Dugongidae in the shape of the skull and the shape of the tail. Manatees' tails are paddle-shaped, while the Dugong's are forked. They are herbivores, spending most of their time grazing in shallow waters, and can weigh anywhere from 500 to 1000 kg. When born baby manatees have an average mass of 30 kg.
Huge, gentle and curious:
Manatees are slow moving, non-aggressive, and generally curious creatures. They enjoy warmer waters and are known to congregate in shallow waters, and frequently migrate through brackish water estuaries to fresh water springs. Their slow moving, curious nature, coupled with dense coastal development, has led to a number of harmful interactions with boat propellers. As a result, a large portion of manatees exhibit propeller scars on their backs. Often the cuts lead to infections which can prove fatal. Internal injuries stemming from hull impacts have also been fatal.
Manatees inhabit the shallow, marshy coastal areas and rivers of the Caribbean Sea and the Gulf of Mexico (T. manatus, West Indian manatee), the Amazon basin (T. inunguis, Amazonian manatee), and West Africa (T. senegalensis, African manatee). They spend half of their day sleeping in the water, surfacing for air regularly, and at intervals of not longer than 20 minutes.
Manatees are herbivores and eat over 60 different plant species such as mangrove leaves, turtle grass, and types of algae, using their divided upper lip. An adult manatee will commonly eat up to 9% of its body weight (approx 50kg) per day. Antillean manatees have been known to eat fish from nets.
Power plants - the local hangout:
Manatees typically inhabit warm, shallow, coastal estuarine waters. Manatees often congregate near power plants, which warm the waters. Some have become reliant on this source of unnatural heat and have ceased migrating to warmer waters. Some power plants have recently been closing and the U.S. Fish and Wildlife Service is trying to find a new way to heat the water for these manatees.
Vulnerable, though not to predators:
All three species of manatees are listed by the IUCN as Vulnerable to extinction. Although manatees have no natural predators, manatees occasionally ingest fishing gear (hooks, metal weights, etc.) while feeding. These foreign materials do not seem to harm manatees, except for monofilament line or string. This can get clogged in the animal's digestive system and slowly kill the animal. Manatees can also be crushed in water control structures (navigation locks, flood gates, etc.), drown in pipes and culverts, and are occasionally killed from entanglement in fishing gear, primarily crab pot float lines. Manatees are also vulnerable to red tides, blooms of algae which leach oxygen from the water. And, as stated earlier, there are a huge number of manatees that have had injuries from boat propellers.
Manatees were traditionally hunted by indigenous Caribbean people. When Christopher Columbus arrived in the region, manatee hunting was an established trade. Native Americans hunted manatees to make war shields, canoes, and shoes, though the manatee was predominately hunted for its abundant meat. Roman Catholic settlers in the area classified the manatee as a fish, since it lived in water, which made it suitable for Friday meals when eating meat was prohibited. Manatees were also hunted for their valuable bones, which were used to make "Special Potions." Up until the 1800s, museums paid as much as $100 for manatee bones or hides. Though hunting manatees was banned in 1893, illegal poaching of the animals continues to the present day.
'Endangered' to 'threatened' in Florida:
On June 8, 2006, The Florida Fish and Wildlife Conservation Commission voted to reclassify the manatee on Florida's list, to a "threatened" status in that state. While none of the state laws protecting manatees have changed, many wildlife conservationists are not pleased with the removal decision. Manatees remain classified as "endangered" at the federal level.
The population of manatees in Florida is thought to be between 2,000 and 3,000.
The natural source for warm waters for manatees during the winter is spring fed rivers. The West Indian Manatee migrates into Florida rivers such as the Crystal River, The Homosassa River and The Chassawohitzka River. The head springs of these rivers maintain a water temperature of 72 degrees year round. During the winter months, November to March, approximately 400 West Indian Manatees (According to the National Wildlife Refuge Service) congregate in the rivers in Citrus County, Florida.
Manatees have been spotted as far north as Cape Cod, and as recently as the late summer of 2006, one made it up to New York City and Rhode Island's Narragansett Bay, as cited by the Boston Globe. According to Memphis, Tennessee's Commercial Appeal newspaper, one manatee was spotted in the Wolf River harbor near the Mississippi River in downtown Memphis, Tennessee, on October 23, 2006, though it was later found dead ten miles downriver in McKellar Lake.
Mermaids? It is thought that sailors created the myth of the mermaid after mistaking manatees for half-fish, half-human creatures.
The popularity of manatees is steadily growing, as is shown by the appearance of many non-profit organizations which benefit manatees, as well as by references to them in the media
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رد: Sea Mammal Groups
The Orca (Orcinus orca) is the largest member of the oceanic dolphin family Delphinidae. They are sometimes referred to as blackfish, a group including Pilot whales, Pigmy and False killer whales and Melon headed whales. It is the second-most widely distributed mammal on Earth (after humans) and is found in all the world's oceans, from the frigid arctic regions to warm, tropical seas. It is also a versatile, deadly predator, eating fish, turtles, birds, seals, sharks and even other juvenile and small cetaceans. This puts the Orca at the pinnacle of the marine food chain. Orcas have been known to attack massive baleen whales, in
particular Gray and Blue whales.
Actually a dolphin:
The name "killer whale" reflects the animal's reputation as a magnificent and fearsome sea mammal that goes as far back as Pliny the Elder's description of the species. Today it is recognized that the Orca is a dolphin rather than a whale and that it is not a danger to humans. Aside from a boy who was charged (but not grabbed) while swimming in a bay in Alaska, there have been no confirmed attacks on humans in the wild. There have, however, been isolated reports of captive Orcas attacking their handlers at marine theme parks.
A sea lion is any of several marine mammals of the family Otariidae. Sea lions are characterized by the presence of external ear pinnae or flaps, long front flippers, and the ability to walk on four flippers on land. Sea lions are generally found in coastal waters of the temperate to subpolar regions of both northern and southern hemispheres.
Sea Lions are often a popular attraction at zoos and aquariums, performing tricks such as throwing and catching balls on their noses and clapping.
Deep sea diver.
Sea lions dive up to 600 feet in search of a meal. Their nostrils automatically shut when they dive so they can stay underwater for up to 40 minutes at a time.
They are great swimmers and can reach speeds of 25 miles per hour, especially when trying to escape predators like whales and sharks.
Females only a third the size of males: The California Sea Lion (Zalophus californianus) is a coastal sea lion of the northern Pacific Ocean. Males grow to 300 kg (600 lb) and 2.4 m (8 ft) long, while females are significantly smaller, to 100 kg (200 lb) and 2 m (6.5 ft) long.
The California Sea Lion has a streamlined body that contains a layer of blubber under the skin to provide warmth and buoyancy. Their large eyes help them adjust to low levels of light in underwater environments, while their whiskers augment their sense of touch. Their nostrils automatically close once they hit the water. Their long front flippers rotate outward for better movement on land, and propel them forward in water, where they are most at home. Males grow a large crest of bone on the top of their heads as they reach sexual maturity, and it is this that gives the animal its generic name (loph is "forehead" and za- is an emphatic; Zalophus californianus means "Californian Big-head").
Sociable sea lions:
California Sea Lions feed on a wide variety of seafood including fish, shellfish, and squid. They are highly sociable and gather in large numbers on beaches and coasts, though they are also often associated with marinas and wharves, and may even be seen on navigational buoys.
Intelligent and often trained:
California Sea Lions are intelligent and adaptable, and are often trained as entertainers at ocean parks and zoos as well as by researchers studying interspecies cooperation in the marine environment. They are also used in military applications as sentries, and for equipment recovery, by the U.S. Navy Marine Mammal Program.
This species usually breeds around May to June and females have a 12 month gestation period. The pup is usually born from June to August, and the mother may give birth in land or water.
There are three subspecies, sometimes considered full species in their own right: Zalophus californianus californianus is the nominate race, found primarily along the Pacific coast of North America. The others are the Galapagos Sea Lion (Z. c. wollebaeki), and the Japanese Sea Lion (Z. c. japonicus) which is now believed to be extinct.
California sea lions are the only mammals whose milk does not contain lactose
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رد: Sea Mammal Groups
The true seals or earless seals are one of the three main groups of mammals within the seal suborder, Pinnipedia. All true seals are members of the family Phocidae. They are sometimes called crawling seals, to distinguish them from the fur seals and sea lions of family Otariidae.
Phocids have no ears:
Phocids are the more highly specialized for aquatic life of the two groups and, unlike otariids, lack external ears and cannot bring their hind flippers under their body to walk on them.
Galumphing on land:
They are more streamlined than fur seals and sea lions, and can therefore swim more effectively over long distances than those can. However, because they cannot turn their hind flippers downward, they are very clumsy on land, having to wiggle with their front flippers and abdominal muscles; this method of locomotion is called galumphing.
Eared seals live more on the land:
The eared seals (or walkinvg seals), family Otariidae, are the fur seals and the sea lions. These are barrel shaped marine mammals, adapted to a semi-aquatic lifestyle. They feed and travel in the water but breed and largely rest on land (or, in some cases, on ice). They are slightly less adapted to the aquatic lifestyle than are the true seals.
True seals don't bark:
Additionally, true seals do not communicate by "barking" like the fur seals and sea lions of family Otariidae. They communicate by slapping the water and grunting.
Efficient, economical movement:
While otariids are built for speed and maneuverability in the water, phocids are built for efficient, economical movement. This allows most phocids to make long foraging trips to exploit prey resources that are far from land, whereas otariids are tied to rich upwelling zones close to their breeding sites.
Important fat reserves:
The phocid reproductive cycle is characterized by temporal and spatial separation between feeding and maternal investment; in other words, a pregnant female spends a long period of time foraging at sea, building up her fat reserves, and then returns to the breeding site and uses her stored energy reserves to provide milk for her pup. It should be noted that the common seal (harbor seal in the U.S.), Phoca vitulina, does not separate foraging and maternal investment; instead, it displays a reptroductive strategy similar to those of otariids, in which the mother makes short foraging trips between nursing bouts.
Lactate or eat:
Because a phocid mother's feeding grounds are often hundreds of kilometers from the breeding site, this means that she must fast while she is lactating. This combination of fasting with lactation is one of the most unusual and extraordinary behaviors displayed by the Phocidae, because it requires the mother seal to provide large amounts of energy to her pup at a time when she herself is taking in no food (and often, no water) to replenish her stores.
Thick, rich-fat milk:
Because they must continue to burn fat reserves to supply their own metabolic needs while they are feeding their pups, phocid seals have developed an extremely thick, fat-rich milk that allows them to provide their pups with a large amount of energy in as small a period of time as possible. This allows the mother seal to maximize the efficiency of her energy transfer to the pup and then quickly return to sea to replenish her reserves. The length of lactation in phocids ranges from 28 days in the Northern Elephant Seal to just 3–5 days in the Hooded Seal. The nursing period is ended by the mother, who departs to sea and leaves her pup at the breeding site. Pups will continue to nurse if given the opportunity, and "milk stealers" that suckle from unrelated, sleeping females are not uncommon; this often results in the death of the pup whose mother the milk was stolen from, as any single female can only produce enough milk to provision one pup.
Because the pup receives the milk energy from its mother so quickly, its development is typically not complete enough for it to begin foraging on its own as soon as the nursing period is complete. Seals, like all marine mammals, need time to develop the oxygen stores, swimming muscles and neural pathways necessary for effective diving and foraging. Because of this, most phocids undergo a postweaning fast, in which they remain on or near the breeding site and live off of the fat stores they acquired from their mothers until they are ready to begin foraging on their own. These pups typically eat no food and drink no water during the fast, although some polar species have been observed to eat snow. The postweaning fast ranges from 2 weeks in the Hooded Seal to 9-12 weeks in the Northern Elephant Seal. The physiological and behavioral adaptations that allow phocid pups to endure these remarkable fasts, which are among the longest for any mammal, remain an area of active study and research.
The largest toothed whale: The Sperm whale (Physeter macrocephalus) is the largest of all toothed whales and is believed to be the largest toothed animal to ever inhabit Earth, measuring up to 18 m (60 ft) long. The whale was named after the milky-white substance spermaceti found in its head and originally mistaken for sperm. The Sperm whale's enormous head and distinctive shape, as well as its central role in Herman Melville's Moby Dick, have led many to describe it as the archetypal whale. Partly due to Melville, the Sperm whale is commonly associated with the mythological Leviathan of Biblical lore. The Sperm whale is the state animal of Connecticut.
Historically the Sperm whale has also been known as the Common Cachalot. The word cachalot is originally Portuguese (cachalote), probably coming from cachola, a colloquial term for head. Sperm whales were hunted until recently in the Portuguese Atlantic archipelago of Azores.
'If I only had a brain...'
The sperm whale has the largest brain of any animal. Its brain is six times the size of a human brain.
However, relative to the sperm whale's huge size, its brain isn't very big.
The largest and heaviest brain:
The Sperm whale is exceptional for its very large head, particularly in males, which is typically one-third of the animals' length. Indeed, the species name macrocephalus is derived from the Greek for "big head" (strictly: long head). In contrast to the smooth skin of most other large whales, the skin on the back of the Sperm whale is usually knobbly and has been likened to a prune by whale-watching enthusiasts. They are uniformly gray in color though may appear brown in sunlight (the "Great White whale" of Melville's novel, if such an animal existed, was an albino, and white sperm whales have been reported in reality as well). Perhaps unsurprisingly, the brain of the Sperm whale is the largest and heaviest known of any modern or extinct animal (weighing on average 7 kg (15 lb) in a grown male). However, the brain is not large relative to body size.
The blowhole is situated very close to the front of the head and shifted to the whale's left. This gives rise to a distinctive bushy blow angled forward. The dorsal fin is set about two-thirds of the way down the spine and is typically short and shaped like an equilateral triangle.
The fluke is also triangular and very thick. Flukes are lifted very high out of the water before a whale begins a deep dive.
Sperm whales have 20–26 pairs of cone-shaped teeth in their lower jaw. Each tooth can weigh as much as one kilogram. The reason for the existence of the teeth is not known with certainty.
Squid research in a whale stomach:
Sperm whales, along with Bottlenose whales, are the deepest-diving mammals in the world. They are believed to be able to dive up to 3,000 meters in depth and 2 hours in duration to the ocean floor. More typical dives are around 400 meters in depth and 30–45 minutes' duration. They feed on several species, in particular giant squid, octopuses and demersal rays. Almost all that is known about deep sea squid has been learned from specimens found in captured Sperm whale stomachs.
Stories about titanic battles between Sperm whales and giant squids which are believed to reach up to 13 m (44 ft) are perhaps the stuff of legend. However, white scars on the bodies of Sperm whales are believed tvo be caused by squid. It is also hypothesized that the sharp beak of a consumed squid lodged in the whale's intestine leads to the production of ambergris, analogous to the production of pearls. Sperm whales are prodigious feeders and eat around 3% of their body weight per day. The total annual consumption of prey by Sperm whales worldwide is estimated to be about 100 million tons — a figure comparable with the total consumption of marine animals by humans each year.
In addition, long-line fishing operations in the Gulf of Alaska have complained that numerous Sperm whales have taken advantage of their fishing operations to eat desirable species straight off the line, sparing the whales the need to hunt them themselves.
The physiology of the Sperm whale has several adaptations to cope with drastic changes in pressure when diving. The ribcage is flexible to allow lung collapse, and the heart rate can decrease to preserve oxygen supplies. Myoglobin stores oxygen in muscle tissue. Blood can be directed towards the brain and other essential organs only, when oxygen levels deplete. The spermaceti organ may also play a role.
Decompression shows in the bones:
While Sperm whales are well adapted to diving, repeated dives to great depths do have long term effects on the whales. Skeletons of Sperm whales show pitting of the bones that is often a sign of decompression sickness in humans. Skeletons of the oldest whales showed the most extensive pitting, whereas skeletons of Sperm whale calves showed no damage. This damage may indicate that Sperm whales are susceptible to decompression sickness, and sudden surfacing could be lethal to them.
Between dives, the Sperm whale will come up to the surface for breath and remain more or less still for eight to ten minutes before diving again.
Social females, loner males:
The social structure of the Sperm whales species divides on sexual lines. Females are extremely social animals, a trait believed to derive from their relatively simple evolutionary path. Females stay in groups of about a dozen individuals and their young. Males leave these "nursery schools" at somewhere between 4 and 21 years of age and join a "bachelor school" with other males of a similar age and size. As males grow older, they tend to disperse into smaller groups, and the oldest males typically live solitary lives. Yet mature males have been stranded on beaches together, suggesting a degree of co-operation not yet fully understood.
Most sexually dimporhic whale:
Sperm whales are amongst the most sexually dimorphic (that is, males and females differ greatly) of all cetaceans. Males are typically 30%–50% longer (16–18 m, 52-59 ft) than females (12–14 m, 39-46 ft) and weigh about twice as much (50,000 kg vs. 25,000 kg, 55 short tons vs 27.5 short tons). At birth both males and females are about 4 m (13 feet) in length and 1,000 kg (1 tonne) in weight.
Decrease because of whaling:
Due to extensive whaling, Sperm whale size has decreased dramatically, mostly because the largest males were killed first and most intensively, for they had more spermaceti (spermaceti oil was of great value in the 18th and 19th century). In a Nantucket museum there is a jawbone of a sperm whale which is 5.5 m (18 ft). The jawbone makes up to 20%-25% of the sperm whale's overall body length. Thus this whale might have been 28 m (90 ft) long, weighing around 150 metric tons (165 short tons). Another evidence of large bulls of the past resides in New Bedford museum, a 5.2 meters (17 feet) jaw of a bull that could have been about 25.6 meters (84 feet) long, weighing about 120-130 tons. In addition, log books found in the Nantucket and Bedford museums are filled with references to bulls that were, considering the amount of oil they yielded, about the same size as these two examples. Today, Sperm whale males average 18 m (60 feet) in length and 52 metric tons (57 short tons) in weight.
In July 2003 a huge blob of white flesh was found washed up on a beach on the coast of southern Chile. The 12-metre-long (40 ft) mass of gelatinous tissue gave rise to speculation that a previously unknown giant octopus had been discovered. However, researchers at the Museum of Natural History, Santiago concluded that the mass was in fact the innards of a Sperm whale, a conclusion drawn by looking at the dermal glands. When a Sperm whale dies, its internal organs rot, until the animal becomes little more than a semi-liquid mass trapped inside the skin. In this case, the skin will eventually burst, causing the internal mass to float free and eventually wash up on the beach.
Dead whales on the beach:
Dead Sperm whales float towards shore quite often. Apart from the disposal issues identified above, beach managers fear that sharks, in particular the Great White shark, will be attracted towards the beach by the rotting flesh, and potentially cause danger to beach users. For this reason, dead Sperm whales are often towed out to sea before they become properly beached. This occurred twice in May 2004, once off Oahu in Hawaii where a dead whale was towed out 35 miles to sea but floated back to shore two days later.
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رد: Sea Mammal Groups
أكاديمية ماركا التعليمية
رد: Sea Mammal Groups
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