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elephant seal adaptions

Dive Response | Oxygen Capacity and Utilization | Energy from Fat

Fasting | Thermoregulation | Delayed Implantation | Sensory Ability

 

Elephant seals have many physiological and behavioral adaptations that help them survive and thrive in the marine environment.

 

The Dive Response

Like all seals, elephant seals undergo a set of physiological changes when they dive – called the dive response or dive reflex.  It includes a significant drop in heart rate, constriction of blood vessels in the periphery, and cessation of breathing. These reactions serve to protect the animal from excessive heat loss and to maximize the survival time without breathing. The figure below show the change in heart rate at sea for both deep and shallow dives.

Interestingly, the seals also cease breathing on the beach, just as they do when they dive. There is a similar, if not as pronounced, change in heart-rate. The dive response.works on land. The following graph shows the heart-rate for the breathing and not-breathing times on land.


Oxygen Capacity and UtilizationFES

Oxygen to support metabolism is carried in three ways by all mammals: as a component of air in the lungs, attached to hemoglobin in the red blood cells and attached to myoglobin, a similar molecule that is fixed in the muscle. While elephant seals dive with almost no air in their lungs, they are 22% blood by weight, as compared to our 7%, and their blood is 33% richer in hemoglobin. Also, the heart and skeletal muscles of elephant seals have a density of myoglobin more than 8 times that of a human. In addition to starting the dive with this very large supply of oxygen, the elephant seal has the ability to utilize almost all of it on every dive, ending dives with oxygen concentration in the veins of less than 5% of maximum.

 

They use this extraordinary capability to dive to great depths and to surface only briefly between those dives. 90% of their time at sea is under the surface -- most of that time 1,000 to 3,000 feet (300 to 900 m) deep.dive chart

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Energy from Fat
energy from fat Blubber is a thick layer of fatty tissue found under the skin in all pinnipeds. Blubber is different from other types of fat in that it is laced with blood vessels and collagen fibers. It functions as an insulating layer, keeping internal organs warm in an ocean environment below 40° F (4.5° C). Blubber also aids buoyancy and streamlines the body for efficient passage through water. Elephant seals are able to metabolize blubber, providing energy. Water is a by-product of metabolism which, carefully conserved, allows them to survive extended periods of fasting.  Blubber may account for nearly 50% of an adult male’s weight at the beginning of the pupping and breeding season (December). By the end of breeding season in March, adult elephant seals of both sexes will have lost about 40% of their weight through blubber metabolism.

 

Thermoregulation

thermoregulate elephant sealsSeals control internal temperatures and reduce heat loss by what is called "countercurrent heat-exchange." As an example, the arteries carrying warm blood to the tail fins are meshed with the veins carrying cold blood from the tail. Inside this mesh, heat is transferred from the arteries to the veins, moving heat to the returning blood rather than losing it to the ocean.

 

At times, the problem on land is removing excess heat from the body. This is accomplished in a number of ways, most prominent being flipping the cool moist sand onto the body, cooling by contact and by evaporation. The seals will also. from time to time. raise a front flipper. There is very little blubber insulation in the "arm pit" and the blood flow is near the surface there, allowing efficient cooling. The seals will often line up along the water's edge and use the cool wet sand as another means of dissipating excess body heat..

 

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Fasting

Except for nursing pups, all of the seals in the rookery are fasting - no food and no water for their entire stay. They survive by metabolizing their blubber, providing energy, nourishment, and water.. Water loss is almost entirely by respiration. Cool air is drawn into the lungs where it heats up to body temperature (slightly higher than ours) and absorbs moisture. When they exhale, any water in that breath is lost. They conserve water in two ways: when resting they do not breathe 60% to 70% of the time (see the chart above) and they capture and recycle much of the water in the exhaled air, This is made possible by an elaborate bony structure, the turbinate process, in the nasal passage that is cooled when inhaling and, in turn, cools the exhaled air, condensing out 70% of water absorbed in the lungs, another example of counter-current heat exchange.

 

Fasting serves a number of purposes. By not foraging in the area of the rookery, they greatly reduce the attraction of predators, making access to the beaches much safer. Also, for the molt and nursing periods, fasting allows those activities to consume a minimum of time, maximizing their foraging time.

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fighting elephant seals

During the breeding and pupping season (December to March), adult male elephant seals come ashore to establish and maintain mating dominance over other males. If a male were to leave the beach, he would lose his mating advantage. Fasting as long as three months, one of the longest mammalian fasts, ensures the male retains mating access to females.

 

Female elephant seals nurse their pups for about a month. Leaving the rookery to forage could result in a female losing her pup, a major cause of pup mortality. Weaned pups (weaners) remain on the beach after their mothers depart. They are able to fast for 8 to 10 weeks in the predator-free zone of the rookery before venturing into the sea to forage.

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Delayed lmplantation

moisture energy conserve elephant sealShortly before a female leaves the rookery after birthing and nursing her pup, she will be impregnated. She leaves the rookery for about two months, returning in April for a month on the beach to molt. On her departure from the molt, the fertilized egg, by that time developed into a cluster of cells known as a blastocyst, attaches to the uterus and the seven and one-half month gestation period begins. This delay in the attachment has a number of important advantages. The female departing the beach after birthing has lost about 40% of the weight she had when arriving on the beach. During her time at sea before the molt she is able to regain about 80% of that lost weight without simultaneously nurturing a fetus. Similarly, she is able to fast during the molt without the resource loss required by gestation. Perhaps the most important advantage of delayed attachment is that it serves to synchronize birthing without synchronizing breeding. The females who gave birth are bred in or around February. However, 15% to 20% of births are to new mothers, juvenile females who are not in the rookery during the birthing/breeding season. They are bred at other times but, like all juveniles, they come to the rookery to molt at the same time as the experienced females. With attachment occurring on departure from the molt, the gestation period of these new mothers-to-be begins at the appropriate time and they will give birth on schedule.

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Sensory Ability

Elephant seals forage at great depth where it is very dark, even during the day. There is no evidence of any echo location ability. Foraging appears to depend upon vision and movement sensitivity of their whiskers - vibrissae. Little is known about the latter sense but the high level of neural connections to the base of the vibrissae suggest they are important for tracking prey. The vision is better understood. Their sensitivity to light is ten times that of a human and is particularly sensitive to the colors of their bioluminescent prey.They share with cats the reflecting surface behind the retina which roughly doubles their sensitivity. Their eyes permit clear vision both in water and in air with a powerful lens responsible for most of the focusing rather than the cornea. Finally, the time to adapt their vision from the bright ocean surface to the dark of the bottom of their dive is very brief; 2 - 3 minutes compared to our 25 minutes.

 

Dive Response | Oxygen Capacity and Utilization | Energy from Fat

Fasting | Thermoregulation | Delayed Implantation | Sensory Ability

 

Known Breeding Colonies | Age Classes

Adaptations | Life on Land & Sea | HIstory of the Colony | FAQs

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Photo contributions by Phil Adams, Joan Crowder, Peter Hemming, Brandt Kehoe, Tim Postiff & Nancy McKarney