Ten centimetres of blubber: a blessing and a curse

Like all true seals, elephant seals have atrophied hind limbs (the equivalent of our legs). Each “foot” is quite distinctive, however, and has a palm which is intended for propulsion in water. On the other hand, they have become unsuitable for any kind of movement on land. Movement on the beach is by means of the flippers, these “arms” are used as supports to enable them to propel themselves on land by making a succession of small bounds.  They can move quickly over short distances in this way whether to return to water, catch up with a female or chase away an intruder.

The elephant seals possess a thick layer of blubber under their skin, which insulates them against the cold, improves their buoyancy and constitutes a very precious reserve of energy for periods of fasting on land. This blubber, which can reach a thickness of ten centimetres, was the reason these animals were intensively hunted from the 18th century which almost culminated in the disappearance of the species by the end of the 19th century. The seal ships pursued the elephant seals on land during the reproductive period, slaughtered them in great numbers and melted down their sub-cutaneous blubber in order to transform it into an oil of very high quality, which was suitable for use in the softening of leather and the lubrication of machines at the beginning of the industrial revolution. The hunting never really stopped until new kinds of oil of mineral origin took the place of the melted blubber. Since the beginning of the 20th century, the northern elephant seals have been protected by American and Mexican laws, which have allowed their population to grow again to more than 120,000 individuals, even though the species was on the brink of extinction. But the current population, built up again on the basis of a reduced genetic diversity, is probably less robust and more sensitive to diseases and effects of pollutants.

The elephant seals spend most of their lives under water only resurfacing to replenish their oxygen reserves. Essentially this is stored in the blood of which they contain a much greater volume than humans even in relation to the body mass.  During prolonged underwater solitary dives, sometimes to depths of 1,000 metres, Mirounga angustirostris mainly tracks fish and squid. Its hunting is helped by its hydrodynamic shape which is suitable for rapid swimming. But it is also helped by excellent vision and a pair of vibrissae, those “whiskers” which are sensitive to vibrations in the water, enabling it to easily locate its prey. It has no known predators apart from killer whales and great white sharks. Despite its ease in the marine environment the elephant seal remains among the most ‘’terrestrial’’ of true seals because each year it spends several consecutive weeks on land.

The reproductive season begins in December with the arrival of large males on the beaches, the strongest acquire a ‘’harem’’ which can count as many as several dozen females. Those wishing to challenge them for possession of the females must challenge the dominant male in a fight preceded by powerful eructations unless they succeed in ‘’picking up” a female on the periphery. The females fertilized during their stay “on the beach” the previous year, return to it between the months of December and February to give birth to a single pup weighing between 30 and 40 kilos at birth. Suckling of the new-born lasts between 24 to 28 days during which the mother, deprived of access to food, loses a considerable amount of weight equivalent to around a third of her body mass. On the other hand her offspring can triple its weight during the same period and reach or even exceed 100 kilos at weaning.