Dive Dry with Dr. Bill

#578: Mating... But No Munching!

Okay, it is time to talk about the way the northern elephant seal (Mirounga angustirostris) rebounded from near extinction just over a century ago. For all you parents with young children, this column will not be suitable reading for your five or even 10 year old... and for all you parents that still believe the stork brings babies, what can I say to warn you? Yes, I'll be focused on the "M" word that sustains the species over time... mating. And for elephant seals, when they do that "M" word, they stop doing the other one, munching! No crackers in their bed.

To get from about 20 to 100 individuals back in the late 1890s to perhaps 175,000 today requires a lot of that "M" word, especially since elephant seals usually have just one pup a year, with twins being fairly rare. Of course China continues to expand even with its one child rule. I had just one child and even I'm expanding... or at least my Buddha belly is!

Females are reported to reach sexual maturity as early as two years with the majority becoming reproductive by 3-5 years. The boys are variously reported to become men between their fourth and ninth birthday, but often are not successful in mating until they are nine to ten. They peak between the ninth and twelfth year. I hope I haven't yet! Mating is strongly polygynous with a single dominant bull defending 30 to 100 cows a season.

Mating requires these pinnipeds to abandon the sea and come ashore. The ocean is their sole source of munchies, but the young pups would never survive if born at sea since they can't instinctively swim. The breeding period runs from about December to March. Large males haul out first to establish their beach front rights. They do so with threats and vocalizations, but will engage in bloody but generally non-lethal battles using their huge mass and sharp canine teeth. Their necks, chest and shoulders are protected with a thickened, keratinized layer of skin.

The dominant bulls that emerge from these battles are referred to as alpha males. Along the six miles of breeding beaches near Piedras Blancas where I filmed, there are an estimated 100 alpha males each defending their part of the beach. Usually only the dominant males get to mate with the females, but subordinate ones at the periphery of the colony may attempt to do so. When this happens, the female often cries out to get the alpha bull to drive him away. Most males die before reaching breeding age, and some that reach old age never get a chance to. The alpha male may sire an estimated 200 to 500 pups during his period of dominance. Sadly, by age 13 the bulls are "over the hill" and don't get any further opportunity to breed since they are out competed by the younger males.

The pregnant girls arrive on the beach the following month and into early February, after the boys have established their positions through fighting. They deliver their pups 2-7 days after arriving. I timed one of my visits for the peak birthing period, mid-January, and the beach was "littered" with hundreds of pups (get it?). I even got to film one delivery. Pups emerge head or "tail" first and the process usually takes less than an hour. It was easy to spot locations on the beach where a new pup was born because the seagulls would flock to it to eat the afterbirth.

The newborns usually weigh in at 70-75 pounds and about four feet in length. Their fur is a dark black, perhaps to absorb the sun's heat during winter until they develop sufficient blubber nursing off their mom. The mother and pup bond immediately through a series of vocalizations and nuzzling that help them identify one another. Females may get aggressive towards other mothers when defending their pups, emitting a growl with an open mouth as a threat display. Funny, I've had some ladies of the human species do that to me!

Stranded on the beach by their maternal obligations, the females fast for about 4-5 weeks while nursing their pups. They may lose half their body weight, converting their blubber reserves into a very fat rich (up to 50-60%) milk. The pups gain nearly 10 pounds a day. By the time they are weaned, they may be 250-350 pounds. Most females reject orphaned pups although some will accept them and nurse them along with their own. Especially resourceful pups may nurse from two or three lactating females and balloon out to 600 pounds!

Towards the end of the nursing period, the female becomes sexually receptive and mates with a male (or two). Mating peaks in mid-February. The male approaches the female, throws one of his flippers on top of her back and grabs the back of her neck with his teeth. How romantic! If she resists (what self-respecting lady wouldn't when mounted by a two-ton gorilla), he may place his body on top of her. Based on my observations, the female flails around, twisting her body in an attempt to escape her destiny. Some succeed. However, it is estimated that 95% of the females are impregnated each year. Although they do not give birth for another 11 months, the actual gestation period is only 7-8 months since the egg undergoes a delayed implantation in the uterus until about three months after actual mating.

With her maternal duties over and next year's pup in the oven, the female abandons the beach and returns to the sea to munch. The pup is not capable of swimming yet and remains on the beach for another one to two months. They form groups and live almost entirely on their blubber reserves. Although somewhat fearful of the water at first, the pups learn to swim and dive near shore. During this period they develop the muscles needed for oceanic existence and also expand their oxygen storage capacity in the blood system and muscles. Their black fur is molted and a new silver coat appears. Finally they head off to the open sea to begin their solitary lives... if they aren't munched on the way out by a great white shark... since they have now officially entered The Mutual Eating Society!

© 2014 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Tenderly the male puts his flipper on her and gives her a little love bite... but may mount
if she resists; mother vocalizing to bond with pup and pup nursing. .

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia