Ever heard of Vitus Jonassen Bering? How about Georg Steller? No? Well, Bering was a Danish cartographer and Steller was a German naturalist. They lived in the early 1700s, and worked together for Imperial Russia, under whose auspices they led expeditions to map the Arctic coast of Siberia.
In 1741, while they were sailing around between Alaska and Russia, in what would come to be called the Bering Sea, the ship carrying Bering and Steller ran aground during a storm, on the shores of what would come to be called Bering Island. (Vitus Bering was notoriously humble.) The island wasn’t inhabited (by humans), and was a pretty desolate place.
Having lost their stores during the wreck, the expedition members were in immediate need to food. The island didn’t offer much in the way of nourishment, but the water around it did, in the form of sea otters and, more importantly, an oceangoing mammal that would be named Steller’s sea cow. (Steller also had a very low opinion of himself.)
Steller wrote about the sea cow in his diary,
describing his amazement at how easy the animals were to capture and kill. All
the crewmen had to do was paddle out a small distance from shore in a lifeboat,
stick a harpoon in one of the beasts, and haul it back to dry land at the end
of a rope. In one instance the crew was even able to forgo the harpoon by
simply lassoing one of the creatures around its tail. This easily obtained source
of food enabled the men to avoid starvation until they were rescued.
Tales of Steller’s sea cows and the otters they swam
with traveled speedily, and ships converged on the Komkandorski (Commander) Islands
(of which Bering Island is one) seeking hides and pelts. In those days, sea
otter pelts were insanely valuable luxury items that were used to make hats,
coats, and stoles for the moneyed elite. In a similar, if not quite as profitable,
vein, sea cows were prized for their meat, hides, and blubber.
To say that both species were hunted relentlessly doesn’t come anywhere close to describing the zealous, greedy slaughter that took place, but the facts make it clear: by 1768 – a mere 27 years after Georg Steller crashed on Bering Island – sea otters had vanished from much of coastal areas of the Bering Sea, and Steller’s sea cow had been driven to extinction.
About the Sea Cow
Steller’s sea cow (Hydrodamalis gigas) was a
sirenian, which is an order of aquatic mammals that dates back to the
Pleistocene epoch. Only two species are extant: dugongs and manatees. Like all
sirenians, sea cows were herbivores and made a living by grazing on kelp. It is
thought that at one time they ranged throughout the Northern Pacific, perhaps
as far south as the waters off what is currently the state of Washington.
Sea cows were enormous. In their heyday, they were
second in size among sea mammals only to whales. They grew to lengths of close
to 30 feet and weighed around 10 tons, making them substantially larger than
dugongs or manatees, which max out at around 9 feet and perhaps 1,500 pounds. Sea
cows had large semi-flexible front flippers, no dorsal fin or hindlimbs, and a
forked whale-like tail fluke. Their thick, rough skin and four-inch layer of
blubber made them well adapted for life in cold water. They were monogamous and
raised their offspring in small social groups, behavior extrapolated from that
of their modern cousins and inferred from historical records.
Twentieth century analysis of sea cow skeletons revealed that the animals were positively buoyant, meaning they were physiologically unable to completely submerge and roamed only the surface area of the kelp forests they called home. This evolutionary adaptation was beneficial to sea cows for millions of years because it enabled them to feed themselves without expending the energy required to dive underwater in search of food.
Then human hunters arrived on the scene, and the sea cows’ positive buoyancy immediately became a detriment. Their slow, docile nature and their inability to escape by plunging down into the safety of the kelp combined to make the sea cows easy pickings for hunters.
Extinction
Extinctions rarely happen for a single reason alone. The majority of the time it is a cascade of events that leads to an animal’s demise. Such was the case with Steller’s sea cow.
As mentioned previously, sea cows shared their habitat with sea otters. Among the things sea otters like to eat are sea urchins. We’ve all seen videos of otters floating on their backs bashing sea urchins open with rocks in order to get at the yummy stuff inside, and that’s what they spent a lot of their time doing when they thrived along the coastlines of the now Komandorski Islands.
See urchins live on the seafloor, and when lunchtime rolls around they are voracious, spiny little piglets, devouring numerous kinds of seaweed, including kelp. In healthy kelp forests, where urchins are kept under control by predators, urchins can’t do much damage. But if the predators are removed, sea urchins grow larger and more numerous, and can devastate kelp by eating the plants just as they are beginning to grow.
I’m sure you can see where I’m heading. When human
hunters killed off the otters, the sea urchins ran wild and killed off the
kelp, leaving the sea cows with nothing to eat. Yes, human predation played a
part in the extinction of Steller’s sea cows, but starvation was equally ruinous.
What’s to Be Learned?
Ecosystems are made up of millions of moving parts, each reacting to the other according to the gradual vagaries of evolutionary pressure. Perturbations can be balanced out through adaptation, if given enough time. However, the abrupt, wholesale removal of vital elements is a trauma too massive for an ecosystem to survive. Evolution doesn’t work that fast.
Sixty-five million years ago a meteor impact unleashed
a cascade of events that brought about the extinction of the dinosaurs. Today, human
beings are inflicting the same level of damage on the global ecosystem.
Except that we are doing it faster than that meteor,
and there’s no sign that we are slowing down.
There's currently a human caused die off of manatees in the Indian River Lagoon. Human activity is killing the seagrass which the manatee eat. They're starving to death here too.
ReplyDeleteMack - I missed your comment somehow. That's terrible to hear about the manatee. Are there plans in place to do anything?
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