Creature Feature: Northern Elephant Seal

Oh, December- the most exciting time of the year! Classes are ending, holidays are approaching, and abundant feasts with family and friends are plentiful. What you may not know, however, is that this season also brings pinnipeds1 (the phylogenetic Order of seals, sea lions, and walruses) ashore to commence their yearly soap opera series, filled with drama, tragedy, and comedy. This is also known as mating season. The award-winning cast of Northern elephant seals (Mirounga angustirostiris) includes alpha males, beta males, females, pups, and weaners (juveniles of 1-12 months), so if you happen to find yourself on the California coast in winter time, grab some binoculars and popcorn for some must-see nature episodes.

Picture 2
Map of the West coast of North America indicating the major northern elephant seal breeding sites.2 (Credit: Encyclopedia of Marine Mammals)

Prologue

In the 1800s, Northern elephant seals were hunted to almost extinction for their blubber (thick fat tissue of marine mammals), with the population dwindling to fewer than 100 seals on Guadalupe Island in Mexico. However, with the help of their protected status (starting in 1922) and the establishment of marine sanctuaries, the current population is now around 160,000 seals along the western Pacific coast!

Picture 3
Northern elephant seal breeding site at Piedras Blancas in San Simeon, CA. (Credit: Wikimedia)

Northern elephant seals spend more than 80% of the year at sea, and are considered one of the most deep-diving mammals, diving to depths of up to 1640 yards (1500m) deep (that is almost a mile down!), for on average of 20-30 minutes. However, they have the ability to stay submerged at depth for up to 120 minutes (2 hours!).2,3 While relatively solitary at sea, their social reunion begins when territorial males come to shore to stake out optimal beach turf for the breeding season in December. Elephant seals have high site fidelity, meaning that although they travel around the ocean most of the year, they come back by the hundreds to the same breeding spot each year. Pregnant females follow the males to these locations to give birth, nurse their young, mate with other males, and then return to sea, leaving behind their weaned pups to figure out how to swim and forage on their own.

Meet the Cast

Picture 4
Alpha male resting with his harem. He has been in many spars as seen by the scarring on his proboscis and chest. (Credit: Nick Chudeau)

Alpha males: Male Northern elephant seals are the protagonists in this soap opera, driving the plot forward. They create opportunities for action scenes and love scenes along the beach. Aside from their humongous size (5070lbs or 2300kg), alpha males can be identified by their developed proboscis (the nose that gives them their name, as it looks like an elephant’s trunk) and chest shield.2 Proboscises are used to resonate their vocalizations to threaten other males5, however they are also used for hydration.6 Adult males fast for up to 3 months during the breeding season, and the compartments in their proboscis can reabsorb moisture from breathing. The characteristic chest shield of the alpha males, a region of the neck, chest, and shoulders of thickened and scarred skin, is associated with fighting during mating season.

As a polygynous species, a male’s main goal during the breeding season is to develop and defend a harem (a group of animals with one dominant male that has exclusive access to a group of females within his territory) of 40-100 females to maximize his mating opportunities. In order to maintain a harem, males must compete fiercely against each other through spars, or battles that can be posturing and vocalizations or escalate to full physical contact. Alpha males must stay ashore from the time they establish a territory, to after females leave post-weaning, which totals to over 100 days of no eating or drinking. Physical battles come with extreme energetic costs, so male elephant seals use unique individualized vocalizations to recognize other males that can provide  information on whether a physical battle is worth their time, energy, and the possibility of giving up their harem.5 (Check out this video for an example of a physical spar and more on cool vocalization research).

Picture 6
One juvenile beta male attempting copulation with a weaner. (Credit: Nick Chudeau)

Beta males: Although there are plenty of males on the beach, only 1% of them (the alphas) actually gain reproductive access to females each year,7 leaving the supporting actor role to the beta male. Beta males may attempt to establish a territory or harem, but are unsuccessful due to lack of experience and/or size and strength. You may be able to spot beta males sneaking around the perimeter of a harem to snag an unsuspecting female in hopes of creating at least one of his own offspring, only to be chased away by the ever-vigilant protagonist of our soap opera!

Picture 7
Two nursing females fighting over the newborn pup. (Credit: Nick Chudeau)  

Females: Female Northern elephant seals may seem like your typical romantic-comedy character, swooning over the biggest alpha male with the best territory; however, subplots emerge as we discover the hurdles that females have to overcome during the breeding season. After an 11-month gestation, females flop ashore and find a place to give birth two to five days after arriving on the beach. They produce a single pup that weighs between 60-80lb (30-40kg) at birth.2 They then nurse their pup for 26-28 days, relying on blubber stores for energy as they fast for that 4-week period, allowing constant access to nutrient-rich, ~50%-fat milk that leaves the pup at a chubby 300-330lbs (140-150kg) by the weaning period! While one pup alone sounds like a manageable handful, the reality is hundreds of other pregnant and nursing females, squawking pups, and competing males trying to control where the females move so that they can stay inside their harem. Amongst the chaos, females can easily lose their pups, and with hormones raging, some females who do may try and steal another female’s pup for her own – talk about drama! After losing over half of their bodyweight due to nursing and fasting, females will mate and then rapidly galumph towards the ocean (avoiding all beta males who may attempt multiple copulations…yikes) to finally get some food (and perhaps some peace and quiet).2

Picture 8
A mother and neonatal (a.k.a brand new!) pup. The pup has black natal pelage that molts into a silvery-gray coat during nursing. (Credit: Nick Chudeau)

Pups: Northern elephant seal pups arguably have the most difficult role in this soap opera, which is simply to survive. Upon first breath, pups must endure sea gulls pecking to gain a placental snack, possible competing females blocking access to their mothers, and the constant risk of being trampled on by fleeing females or fighting males. In fact, only 5% of all elephant seals survive to maturity7, with many fatalities occurring during the first few days of life. If they do avoid being crushed and are able to suckle, they gain up to 10lb (4.5kg) per day2,8 – can anyone say growing pains? At around 4 weeks, pups are left abruptly to figure out the world and how to continue surviving in it on their own, with nothing but a thick layer of blubber to protect them (and hopefully last them until they figure out how to hunt for food).

Picture 9
A Northern elephant seal weaner goofing around with its flippers. (Credit: Robert Schwemmer, CINMS, NOAA Library)

Weaners: The dynamic, comic-relief character that also faces both drama and various challenges is the Northern elephant seal weaner. Weaners are aptly named, as they are in the weaning period and are no longer nursing from their mothers. The thick layer of blubber from nursing allows 2 months of fasting as weaners figure out important life skills.8  However, some weaners, known in the scientific community as “super weaners”, attempt to rig the system and will sneak around the remaining nursing females, attempting to suckle to gain additional weight (up to 500lb or 220kgs) at just 2 months of age.8 This fasting period is a one of discovery, but it is also a literal sink-or-swim situation as the weaners must learn important lessons to survive: how to swim, how to hunt, and how to avoid getting violently mounted by testosterone driven-males that have had no chance to mate.2 Other seemingly less important lessons include discovering what happens when they chase after shorebirds, the feeling of rolling around in dried stinky kelp compared to fresh wet kelp, how to smear feces on their weaner friends or how to grab their own back flippers with their mouths.

Epilogue

Assuming all of our characters survive the dramatic mating period and time at sea each year, the only other time elephant seals haul-out (come ashore) is for their catastrophic molt, which is not as scary as it sounds. Unlike most mammals, which shed hair throughout the year, elephant seals shed the first layer of skin as well as all the hair on their body in 3-5 weeks. The amount of metabolic energy it takes to molt in this way require the seals to stay out of the water, and use blubber stores to maintain their energy requirements during that molting period.4  While we get a dramatic window into the lives of Northern elephant seals during the mating and molting periods on the beach, it is only a snapshot of their annual cycle, and mysteries of what they do while they are out at sea remain. With the help of tracking technology, researchers are getting a better idea of what elephant seals are doing (and eating) in the open ocean, so coming soon to a theater near you, Keeping up with the Northern Elephant Seals: Ocean Edition.

Fin.

(or should I say Flipper.)

Karli Chudeau is in the Animal Behavior Graduate Group and a part of theUC Davis Center for Animal Welfare. She is interested in conservation management and assessing animal welfare in wildlife rehabilitation settings. Her current research examines how we can use behavioral management interventions, such as environmental enrichment, to improve reintroduction success with pinnipeds. She is also an avid ocean nerd.

References

1 McGinnis, S. M. & Schusterman, R. J. (1981). Northern elephant seal—Mirounga angustirostris. In “Handbook of Marine Mammals” (S. H. Ridgway, and R. J. Harrison, eds), Vol. 2, pp. 229–350. Academic Press, London, Seals.

2 Hindell, M.A. & Perrin, W. (2008). Elephant Seals Mirounga angustirostris and M. leonina.  Encyclopedia of Marine Mammals (2nd ed., pp. 366).  Burlington, MA: Academic Press.

3 Robinson P.W., Costa D.P., Crocker D.E., Gallo-Reynoso J.P., Champagne C.D. et al. (2012). Foraging Behavior and Success of a Mesopelagic Predator in the Northeast Pacific Ocean: Insights from a Data-Rich Species, the Northern Elephant Seal. PLOS ONE 7(5), e36728.

4 Champagne, C. D., Houser, D. S., & Crocker, D. E. (2006). Glucose metabolism during lactation in a fasting animal, the northern elephant seal. American Journal of Physiology-Regulatory. Integrative, and Comparative Physiology, 291(4), R1129–R1137.

5 Casey, C., Charrier, I., Mathevon, N., & Reichmuth, C. (2015). Rival assessment among northern elephant seals: evidence of associative learning during male–male contests. Royal Society Open Science, 2(8).

6 Huntley, A. C.; Costa, D. P. & Rubin, R. D. (1984). The contribution of nasal countercurrent heat exchange to water balance in the northern elephant seal, Mirounga angustirostris. Journal of Experimental Biology, 113, 447–454.

7 Boeuf, B.J. (1994) Elephant seals: population ecology, behavior, and physiology. Berkeley, CA: University of California Press.

8 Riedman, M., & Le Boeuf, B. (1982). Mother-pup separation and adoption in northern elephant sealsBehavioral Ecology and Sociobiology, 11, 203-215.

 

 

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