Saturday, January 3, 2009

Ditches as wildlife habitat: Elephant seals.

A juvenile male Northern Elephant Seal has decided to take a breather in a roadside drainage ditch in Saanich, which is on Vancouver Island near Victoria. There was footage of the creature on the local news, opening its mouth, baying and snorting at people. It appears to be in good shape, but in a place one would more typically expect to find an abandoned shopping cart. Local residents were shown doing their best, making sure the seal was safe from cars, dogs, other people, etc.

In November, an adult male of same species turned up dead at Nanaimo, which is farther north on the east side of Vancouver Island. Because of its impressive size, that creature created quite a different stir, and there was considerable speculation on the significance of its appearance -- as if it had been a visitation from a sea monster.



Adult male Northern Elephant Seal, Mirounga angustirostris. Image from http://www.britannica.com.

How did it get there? What happened to it? The second question was answered in part by a necropsy. The first serves to underscore a lack of knowledge of this species, which as far as was known, rarely appeared in British Columbian inshore waters -- a point not made in the news report of our much smaller friend in the ditch.

Adult Northern Elephant Seals can be enormous. Females measure about three metres and weigh up to 2000 pounds. The male, whose elongate, rubbery proboscis provides the name for the species, can be five metres long and weigh more than 4000 pounds. Prized for the oil in their blubber, elephant seals were hunted to near extinction in the late nineteenth century. The surviving population was declared protected by Mexico in 1922, and soon after the U.S. granted protected status. Free from hunting pressure, numbers increased rapidly. There are now more than 150,000 elephant seals, with large breeding colonies re-established on beaches and rocky headlands along the Californian and Mexican coasts.

Elephant seals migrate northward into British Columbia’s outer waters and beyond, and then back to southern haul-out sites, twice a year. The longest journeys are by adult males, some as far as between northern Mexico to the Gulf of Alaska. They remain at sea for months on end, usually alone, often thousands of miles offshore, feeding on deep-water fish and squid.

Their life at sea is a life underwater--deep underwater. I once attended a talk by a marine mammalogist who studied the diving physiology of these animals. He and his students ventured onto haul-out beaches in central California, and super-glued depth-recording transmitters to the resting behemoths. I remember the precipitous stock market-like diagrams on the screen. Elephant seals dove to incredible depths. Most dives were in the order of (only) 300 to 400 metres, but some were as deep as 1500 metres, the greatest depths known for air-breathing vertebrates. Also astounding --almost ninety percent of the time in the open ocean was spent submerged, usually in half-hour stretches, with rarely more than five minutes resting at the surface between dives. No wonder they are seldom seen. An elephant seal’s head is bigger than a breadbox, but next to invisible in the waves.

Elephant seals return south twice a year, once to breed, which happens in the winter months, and once again in time for what is known as a “catastrophic molt.” The deep diving necessary to obtain food requires that oxygen-rich blood be diverted away from the skin, to internal organs. Eventually the skin deteriorates to the point that its outer layers, along with its hair, sloughs away. When this happens, it is best to be high and dry to avoid hypothermia. The molt occurs in spring for adult females and juveniles, and in mid-summer for adult males. The seals remain on land without food or water until blood vessels extending through the thick blubber nourish the layers of tissue, stimulating the regeneration of outer skin and hair. Then off they go again, back to sea, an underwater, upside-down leap-frog into northern feeding latitudes.

Could the Nanaimo animal, and now, the juvenile male, be signs of things to come? As numbers of elephant seals continue to rise, perhaps individuals will be encountered in B.C.’s inner waters more frequently. But also, sadly, perhaps more will be found dead, not of natural causes. The Nanaimo animal was a healthy bull that in November would have been on its way south to try to establish a harem (only the fittest males mate, and with numerous females). Unfortunately, as indicated by the necropsy, that one’s amorous hopes were cut short by fatal injury to its backbone and ribs. Most likely it was struck by a large, fast-moving vessel, a thing as foreign and unknowable to an elephant seal as elephant seals are to most of us.

But now at least we have one new datum to add, regarding preferred habitats.

5 comments:

pinguinus said...

This is a really interesting post. I'd heard about whales suffering fatal collisions with ships before, and of course manatees, but not elephant seals.

And I'm oddly charmed by the vision of a ritzy suburbanite posting cardboard signs around an elephant seal in a ditch.

Hugh said...

Beached/stranded sea mammals bring out the heart-warming best in people. I've often thought that much of the strife in the world could be swept aside if more sea mammals could be convinced to strand themselves.

PSYL said...

Well, how long does these "molting" last? A ditch is certainly no place to be for such these magnificent giant.

But yes, most people does care about stranded sea mammals, since they are so exotic and special. Although I wonder what the successful rate is for returning these animals safely back into the water.

BerryBird said...

What amazing creatures! I'm glad the neighbors are keeping the dogs away -- the little guy looks to be of fairly modest size for his kind.

Hugh said...

PSYL, from what I've read, it shouldn't be molting now (or where it is). Juveniles molt in March, 100s of miles south of where it is. Hopefully it will safely cross the road and get back in the water and be on its way.

BerryBird, Yes, it's a little one. A yearling, maybe?