September 28, 2017
By Liz Clift
Sea Otter Awareness Week is September 24-30, 2017
This summer, I had the opportunity to watch an otter hunt in the surf off the coast of Olympic National Park, in Washington state. The otter rode the waves in, close to the shoreline, and then swam back out, repeating this routine a couple of times before settling on a rock to watch us humans.
Sea otters (Enhydra lutris) are the heaviest members of the weasel family (male otters weigh up to 100 pounds), and unlike other marine mammals, lack a layer of blubber to help keep them warm. Instead, they have the densest fur in the animal kingdom (as many as a million hairs per square inch). This means that though they may look wet, the water isn’t actually penetrating all the way to their skin.
In fact, sea otter pups have such dense fur, they can’t dive under water until they get their adult fur. This is likely a survival adaptation: this dense fur will help keep them warm and also allows the mother to safely leave their pups floating on the surface of the water while they hunt for food.
Like other members of the weasel family, sea otters are carnivores. They eat urchins, shellfish (including mussels and clams), a variety of snails, squid, and a few dozen other marine species. Sea otters may store food they’ve gathered—or a favorite rock—in the large sections of extra skin near their armpits. This extra skin acts as a pocket (and who doesn’t want more pockets??).
A male might eat approximately 20 to 25 pounds of food a day! Much of this eating occurs on the surface of the water, and an observer might see an otter floating on its back and smashing a shellfish against a rock the otter has balanced on its chest in order to get at the meat.
Of course, if you’re lucky enough to see sea otters regularly, you’ll notice that they float on their back for more than just eating. They’ll also casually float in groups, called rafts (and these rafts may include hundreds of individuals!) to rest. When they’re resting, they often wrap themselves in kelp to keep themselves tethered to a single area, and mothers will also do this to their pups.
Otters play a valuable role in kelp forest ecosystems by helping control the sea creatures (including sea urchins) that would otherwise eat (and devastate) these kelp forests. Unfortunately, due to fur trading, their historic numbers have plummeted, which means these ecosystems have changed. To give you an idea of the scale of devastation around the sea otter fur trade here are some numbers:
Although they have made a fairly remarkable recovery, sea otters aren’t in the clear yet. They remain on the IUCN Red List (endangered) and now face threats of infectious disease. As recently as 2015, hundreds of sea otters showed up sick or dead along Alaska’s southern coast as the result of toxins from harmful algal blooms and bacteria. There’s also the possibility that orcas (aka, killer whales, Orcinus orca) have started to eat otters as their other food resources have disappeared, although even if this is true, it does not account for the large otter die-offs.
As sea otter populations to continue to fluctuate, we should consider how this impacts our coastal ecosystems in the areas where they live—and how this, in turn, impacts our local economies since the kelp forests that rely, at least partially, on otters (at least on the west coast) also provide shoreline protection against waves, and foster greater biodiversity of fish, crustaceans, bivalves, and other animals.
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