Dive Dry with Dr. Bill

#567: That's a LOT of Bull

This time of year the thoughts of many turn toward Christmas even though Christ was apparently a Gemini just like me and Santa Claus... well who knows what sign he was born under. Since I'm probably on Santa's naughty (but nice) list, I don't expect much other than coal in my stocking. My thoughts turn toward something few here in SoCal give much thought to. That's right, my mind focuses on another event in December... the appearance of the elephant seals further north on our California coast.

In years past I seriously doubted my 25-year old Toyota Tercel could make the drive up Highway One since it was "uphill," so my twice annual pilgrimages there were suspended a long time ago. This year I packed my camping and video gear (plus a few clothes) into my "new" Corolla LE and headed up towards San Simeon. Most people stop in that stretch of Highway One to view the opulence of William Randolph Heart's castle. Not me.

Back in the fall of '90 or '91 I was on a UCSB marine botany field trip to study the intertidal at the nearby Pt. Piedras Blancas lighthouse. While the students were working their transect lines, I walked around to the other side of the lighthouse... and came face-to-face with about a dozen elephant seal bulls (Mirounga angustirostris) or sea elephants as they are sometimes called. Since some males can weigh up to 5,000 pounds, that's a lot of bull and I was way out of my weight class! Even the much daintier ladies can reach up to 2,000 lbs so I wouldn't face off with them either.

That was apparently the first year northern elephant seals appeared at Piedras Blancas. I was aware of their presence at Año Nuevo near Santa Cruz beginning in the 1950s, but had no idea they were colonizing this new beach head. Historically, this gargantuan marine mammal ranged from Alaska to Baja California. Hundreds of thousands of these behemoths roamed the waters of the eastern Pacific. However, beginning in the 1700s they were hunted for their oil like their distant whale relatives in the days before drilling for petroleum replaced these sources. Charles Scammon reported that an 18 ft male yielded 210 gallons, enough to fuel my golf cart for many years!

By the late 1800s they were thought to be extinct. Then in 1884 an expedition from the Smithsonian found eight individuals on Guadalupe Island off Baja California... and promptly killed seven of them for their collections. Needless to say, many biologists in that era were not terribly enlightened. Had those been the only surviving elephant seals, the "recovery" of the population would have been impossible with just a single individual. Remember, in mammals it takes two to tango... er, "tangle." Apparently there were a few other individuals more adept at hiding their massive bulk from these biologists.

When a species undergoes an extreme reduction in population due to natural causes such as an El Niño, massive storm, epidemic disease; or by extreme exploitation as in the case of the northern elephant seal; we refer to this as a bottleneck. Most of the genetic diversity of the population is eliminated and the population "recovers" with just a small fragment of its original DNA. Scientific studies of their genes indicate that the current population of around 125,000 individuals suggest this bottleneck involved less than 20 individuals. Hmmm, if Noah only took two of each species onto the Ark, that would create a disastrous genetic bottleneck!

The northern elephant seal has a close relative below the equator, the southern elephant seal (Mirounga leonina). This species was not as extensively hunted as its northern relative and did not suffer from such an extreme bottleneck. It is a larger species than ours with males reaching weights of over 8,000 pounds. Females are much smaller than the males.

Since there are only these two species of elephant seal in the world, and my mind dwells on ecological and evolutionary relationships in critters, I have to wonder about the link between the two. Phocid seals are believed to have originated and evolved initially in the northern hemisphere, then entered the southern hemisphere about 10 million years ago. Elephant seals are thought to have developed in these southern oceans. So how does a scientist like myself explain their appearance way up north (to Alaska)?

One possible explanation is that the two species evolved independently, one in each hemisphere. This would be a form of convergent evolution with independent origins. Personally, I find that highly unlikely but then I'm no marine mammalogist. I think it more likely that at some point when the Earth was in a cold climate phase, and the warm waters of the tropics constricted to a narrow band at the equator, that some elephant seals migrated north and entered our waters. Then climate warmed and the tropical waters expanded forming a barrier. However, elephant seals dive very deep... down to a mile below the surface and are said to migrate 13,000 miles a year. Perhaps they could cross the warmer tropics by submerging often. Of course as our waters cool, I'm hoping to migrate... to those warmer waters!

© 2013 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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Elephant seal viewing point at Pt. Piedras Blancas and big bull vocalizing;
youngsters snoozing and male showing proboscis that gives them their name.

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia