Dive Dry with Dr. Bill

#143: Northern Elephant Seal

Africa is a dream destination of mine. My interest is not in bushwhacking through the jungle or watching herds of herbivores get munched on by the lions and tigers and bears (well, at least the first two). I want to go there to dive. The Red Sea, South Africa, Tanzania, Mozambique and Madagascar all have fascinating dive sites that appeal to me. Yes, I know that the "roar of the jungle" (or more probably the savanna) is supposed to be very exciting... but lions and elephants are not my primary interest.

Okay, now how do I segue from that paragraph to the rest of this column about marine life? Perhaps more of my readers have heard the African elephant "trumpet" than the northern elephant seal. Both of these creatures are gargantuan, but only one lives in the waters around Catalina (although elephants are known to swim across miles of ocean to get to offshore islands).

The male northern elephant seal may reach 15-18 feet in length and weigh as much as 6,000 pounds, making them the largest of the seals and sea lions! They become sexually mature between three and six years of age. At this time they develop the large proboscis or "nose" that is responsible for their name. Females are "only" 9-12 feet long and weigh less than a ton. As in our species, the ladies live slightly longer (15-18 years) than the men (12-13 years). Females are capable of reproducing as early as age two, but most practice celibacy until they are four years old (hmmm, almost 18 in human years).

Elephant seals spend most of their lives out at sea. They migrate twice a year with routes as great as 6,000 miles. These seals are incredible divers, especially the females which are capable of descending to more than 5,000 feet... without a SCUBA tank. These "free divers" normally hold their breath for around 20 minutes but are reportedly able to stay underwater for up to 80 minutes. One report even stated up to two hours. Their ability to store up to 95% of their oxygen in their blood and muscle tissue helps make this possible. My lung capacity tested very high at our annual health fair, but I can't touch that record. If I could, it would surely cause a dip in the profits of our local dive shops.

These behemoths come to shore when it is time to give birth and mate. I guess they have no interest in joining the five-fathom club (the underwater equivalent of the "mile high club" for airline passengers). Females give birth in January and February, and nurse their young for nearly a month. To do so they must make frequent trips out to sea to feed. During all this, the bulls engage in a typical male pastime... establishing dominance by fighting. Males are at their peak weight and health at the start of mating season. Of course they are much wiser than the young guys outside the Chi Chi Club. Most of their combat is ritualized in the form of body displays and vocalizations, with actual physical combat a rarity.

Following the fighting, the dominant or alpha bulls establish their harems. They may mate with as many as 50 females. Less than 33% of the male population gets to breed each season. Many males never do. For the lucky ones, mating takes precedence over munching. They may not feed during the entire breeding season (several months) and may lose up to 1,500 pounds. Although this time is spent on sandy shorelines, I don't think they follow the "South Beach Diet." After nursing their pups and mating, the females are also emaciated (having lost up to 500 pounds) and return to the sea for about three months to feed.

The fertilized egg may delay implantation in the uterus while the female feeds and regains her health. The young are born in late fall (Nov.) or early winter. They weigh about 70 pounds, but quickly "bulk up" (without steroids) thanks to the mother's milk which may be more than 50% fat. Some pups become obese (up to 600 pounds) by slyly feeding from more than one female, although this is the exception. Pups may get separated from their mothers and die of starvation. Pup mortality is fairly high, especially during El Nino years when food for their mothers may be scarce. The mother leaves the pup after about a month. The 250-400 pound pups spend a few months playing on the beach and acquiring swimming skills before they enter the water in May to feed.

Squid appears to be the number one item on the menu. Elephant seals will also eat octopus, sharks, rays and fish like the Pacific hake. Great white sharks and killer whales are their only real predators. However, in the 1800's humans hunted these animals in large numbers for the oil rendered from their thick blubber. It was used in lamps, for lubrication and in making many other products. A large bull could yield nearly 25 gallons. By 1900 these seals were nearly extinct. The population was estimated at less than 100 (perhaps less than 20), and was centered around remote Isla de Guadalupe, Mexico (where my great white shark diving occurred last year). The Mexican government instituted protections for this remnant population.

Later, in 1972, the United State's Marine Mammal Protection Act made it illegal to hunt all seals and other marine mammals. Today the population may be as high as 120,-150,000 individuals. As it grew, new areas were colonized along our coast including Ano Nuevo Island near Santa Cruz and by the lighthouse at Point Piedras Blancas near San Simeon. However, the genetic health of the population is not good since all current individuals descended from just a few (20-100) animals from the Guadalupe population. When this happens, it is called a "genetic bottleneck." The low genetic diversity may make the population less adaptable and more subject to diseases. The same thing occurred a few years ago when the vast majority of Catalina Island's fox population was decimated due to canine distemper. Hopefully our foxes will regain some of their past genetic diversity as they recover.

© 2005 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Northern elephant seal juvenile discovered under the pilings when the Terminal Building
(now Armstrong's and the Busy Bee) was rebuilt in the early 1980's.

This document maintained by Dr. Bill Bushing.
Material and images © 2005 Star Thrower Educational Multimedia