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the Legacy continues…………………….
Gregory R. Mann, Ph.D. {ret.}

World of Pinnipeds

Seals, Walrus and Sea Lions are marine mammals called “Pinnipeds” that differ in physical characteristics and adaptations.


Have you ever wondered about the main differences between Seals and their “second cousins” the Sea Lions? Both Seals and Sea Lions together with the Walrus, are “Pinnipeds” which means “fin footed” in Latin but a Seal’s furry, generally stubby front feet — thinly webbed flippers actually, with a claw on each small toe — seem petite in comparison to the mostly skin-covered, elongated fore flippers that Sea Lions posses. Secondly, Sea Lions have small flaps for outer ears. The “earless” or “true” Seals lack external ears altogether. You have to get very close to see the tiny holes on the sides of a Seal’s sleek head. Third, Sea Lions are noisy. Seals are quieter, vocalizing via soft grunts.untitled

Fourth, while both species spend time both in and out of the water, Seals are better adapted to live in the water than on land. Though their bodies can appear chubby, Seals are generally smaller and more aqua-dynamic than Sea Lions. At the same time, their hind flippers angle backward and don’t rotate. This makes them fast in the water but basic belly crawlers on “terra firma”, latin phrase meaning “solid earth” referring to dry land. Sea Lions on the other hand, are able to “walk” on land by rotating their hind flippers forward and underneath their big bodies. This is why they are more likely to be employed in aquaria and marine shows. Seals are less social than their Sea Lion cousins. They spend more time in the water than Sea Lions do and often lead solitary lives in the wild, coming ashore together only once a year to meet and mate. Sea Lions congregate in gregarious groups called herds or rafts that can reach upwards of 1,500 individuals. It’s common for scores of them to haul out together and loll about in the sand, comprising an amorphous and a rather extremely strong smelly pile in the noonday sun. Possessing a very strong oder from their accumulated excrement called Guano, you can smell a large congregation of pinnipeds whether Seals, Sea Lions or Walrus at about 4-miles downwind.

The long, strong, flexible flippers can support Sea Lion’s weight on land, enabling them to walk on all fours in a partially upright position. A Seal’s front flippers are short and not very strong. On land it has to move much like a caterpillar, inching itself along on its stomach. Because of weak front flippers, Seals use their hind flippers to propel them through the water in a side-to-side, fish-like motion. The front flippers do the steering. Sea Lions on the other hand, propel themselves by flapping their powerful front flippers like wings and steer by pointing their heads, necks and bodies in the direction they want to go. Seals are at a slight disadvantage for depending on their hind flippers for propulsion. Their natural predators Killer Whales and sharks, approach from behind. An injury to a Seal’s hind flippers greatly decreases its chances of surviving an attack. A Sea Lion however, might  be able to escape.


Otariidae (“eared” seals)

eared seal

Otariids have visible external ear flaps (pinnae) and an elongate neck. They swim using their long front flippers for propulsion and hind flippers for steering. On land, otariids are agile and quadrupedal: able to pull their hind flippers up under the body and extend the front flippers for four-legged movement.

Adult otariids are sexually dimorphic: males are nearly twice as large as females, and have thickened necks and pronounced skull crests. Females breed with dominant males that establish and defend territories on breeding beaches or rookeries. Pups are born on the rookeries and may be dependent on their mothers for a year or more.


Phocidae (“earless” seals)

earless seal

Phocids have no visible external ear flaps (pinnae). They have short necks and short front flippers, and cannot pull their hind flippers under the body while on land. Although graceful swimmers, phocids are not agile on land and typically “phocidulate”; that is, they move by undulating or heaving the body in a caterpillar-like manner.

Sexual dimorphism is rare in adult phocids (seen only in elephant seals); males and females are generally similar in size and shape. Phocids breed in the water, on shore, or on ice, but (except for Elephant Seals) don’t breed on rookeries. Pups grow at an incredibly fast rate and are weaned young and abruptly after brief lactation during which their mothers probably fast.


Odobenidae (walrus)

walrus

The Walrus body form combines phocid and otariid traits. They have no external ear flaps (pinnae) but move quadrupedally on land. The upper canines in both sexes elongate and develop into tusks.


More Interesting Facts

  • Pinnipeds are believed to have evolved from bears and otters which are land animals.

  • Earless seals are like many species of owls, don’t have ears rather they have ear openings.

  • All earless seal grunt or flap on water to communicate with the other seals and they don’t prefer making loud voices.

  • A large body with less fur differentiates Sea Lions from the Fur Seals.

  • The Walrus is now the only surviving member of the “odobenidae” family.

  • Walrus can be recognized from a long distance because of its tusk and wrinkles. The bulk of fat under its belly makes movement difficult and therefore it can be seen lying lazily on ice for hours.

  • Walrus use their tusk to walk hence they are termed as ‘tooth-walking’ mammals. These tusks are also used to create holes in the ice and breathe under the sea covered with ice.

  • Previously, the Walrus was included in the “otariidae” family along with the eared seals, but later the researchers identified their squirt and suck method of feeding on mollusks. This unique feature of a Walrus differentiates it from other pinnipeds.

  • The reproductive behavior of all the pinnipeds, except Walrus can be easily recognized as Walrus prefer to copulate in remote locations or under water.

  • Due to the presence of postpartum estrus, the female pinniped can mate soon after giving birth.

  • The lactation period is different for different species. Mothers belonging to “phocid” family feed the pup for 4 to 50 days while those belonging to the “otariidae” family spends 4 to 36 months feeding the pups.

  • After the lactation period, the mother pinniped moves out to feed itself and on its return, the next task is to search for the pup out of the large group. She can easily identify its baby from other similar looking pups by making a call that the baby replicates.

  • In polar areas, pinnipeds stop their blood flow to the skin surface in order to prevent heat from escaping their bodies, while reverse action is performed in warm areas. They send blood towards the extremities in order to release heat from the body.

  • Pinnipeds have the ability to control their heart rate while diving; this is the reason why they are found to be sleeping in deep waters for extended period of time. A study shows that they can reduce their heart rate by 50-80%.

  • They can dive up to 1,700 feet deep under water and can stay under up to 40 minutes.

  • Eared seals have very good hearing power, irrespective of the fact that their ears are small.

  • The Leopard Seal is the only pinniped that eats penguins. It has also been known to be aggressive against humans and has attacked humans of which seven have been fatal.

  • Sea Lions can run with a speed of 25-30 kilometers per hour, faster than human. They might look like a crooked human while running.

  • The fur or hair present on the outer body of a pinniped act as water repellents while the underfur insulates it from the outside temperature. Along with this fur coat, they also have blubber to store fat which can be used in case of food scarcity.

  • The eye membrane protects their eyes under the water. This is the reason why pinnipeds can see below and above the surface.

  • Pinnipeds can easily hear sounds under the water with the help of whiskers and sensors in their skull.

  • They have strong resistance to accumulated lactic acid as compared to other mammals.

  • These semi-aquatic animals can hold their breath for almost two hours underwater.

  • Most of the species of pinnipeds go through the molting process every year. During the period of molting, they shed their fur coat or skin and replace it with the new one.

  • The pups of Fur Seals are susceptible to hypothermia as they are not born with dense and insulated fur coat. During their first molt, they replace the thin layer on their skin with an adult coat.

  • The pinnipeds living in polar regions rely on blubber and dense fur coat to preserve heat inside their body, while those living in areas with warmer climate keep themselves cool by resting in shade and hiding under the thin layer of sand.

  • The lung system of pinnipeds has airways supported by cartilage, a flexible connective tissue; smooth muscle and alveoli that completely collapse during deeper dives.

  • A respiratory collapse is considered as a disease in humans but pinnipeds can easily re-inflate their lungs in the case of lung over-emptying. But how? It is possible because of the presence of surfactant system that acts as an anti-adhesive to cope up with the problem of respiratory collapse.

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