SEA OTTERS: Marine Mustelids with an Appetite!

And God said, Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the earth in the open firmament of heaven.  And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good.  (Genesis 1:20-21)

Sea Otters:   Marine Mustelids with an Appetite!

Dr. James J. S. Johnson

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Sea Otters are surely the cutest marine mammals who live in the seawaters off Alaska’s southern coastlines – they float on their backs, their whiskery faces look wise and kind, sometimes they hold hands (paws), and they care for each other.

The Northern Sea Otter (Enhydra lutris) is the only true “marine mustelid” – i.e., it is a member of the category of mammals called mustelids (the weasel super-family), all the other of which live mostly on land, even its “cousin” the North American River Otter (Lontra canadensis).   It is the smallest of marine mammals – much smaller than cetaceans (such as whales) and pinnipeds (such as walrus and seals) – with male adults weighing from about 80 to 100 pounds, and female adults weighing about 50 to 70 pounds.  Unlike other weasel-like mammals, Sea Otters live in seawater – even giving birth in seawater!

Sea Otters, unlike blubbery whales and walruses, are relatively thin – yet they need to survive the super-cold waters that blubber-loaded marine mammals live in. How do the Sea Otters do it? Unlike pinnipeds and cetaceans, sea otters have no blubber, so their fur must keep them warm.

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Sea otter fur is the densest of all mammals (almost 1,000,000 strands of hair/square inch!), consisting of waterproof exterior “guard hairs” over a dense layer of dry underfur, so it insulates from environmental temperature extremes:  “air trapped in its fine fur keeps it warm as well as buoyant.”  [Quoting John Whitaker, Jr., National Audubon Society Field Guide to North American Mammals (1998), page 786.] Unlike animals that periodically “molt” (like birds and reptiles), sea otter fur is shed gradually, year-round.  To stay warm in the super-cold waters off Alaska’s southern coasts, Sea Otters rely on more than their providentially thick fur, they also eat often and a lot – they have a high metabolism!

As a carnivore, the Sea Otter eats mostly animals – including clams, sea worms, squid, octopus, abalone, sea urchin, starfish, and crabs (especially Dungeness Crabs). However, Sea  Otters  consume  so  many  Dungeness crabs,  so  quickly, that  southern Alaska’s  crab  fishermen  are  losing  out – so not everyone thinks of Sea Otters as being “cute”.

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Some shellfish are hard to eat, due to tough exoskeleton shells, but Sea Otters are up to the task – they use rocks to crack open clam shells, or abalone shells – sometimes using a rock as an anvil.  Diving Sea Otters also use rocks to dislodge shellfish (such as clams or mussels) that are firmly attached to an underwater substrate.

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Sea Otters are so intelligent, learning to adapt to new information, that they have been observed ripping open metal drink cans, in search of juvenile octopus, because they have learned that small octopuses often use metal drink cans (discarded by human litterbugs in Alaska’s coastal waters) as hiding-places, similar to how hermit crabs will “recycle” uninhabited shells.

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In fact, God has designed anatomical “pockets” for carrying both rocks and food items, when a Sea Otter is diving underwater.   Sea  otters  have  loose  armpit  skin (a “pouch”),  for  carrying food, or rocks  (thus  freeing  up  their  “hand” paws)  to  use  as anvils  (when  they crack  open  sea urchins or bivalves, like  clams  and limpets and  mussels).  Webbed  hind  paws  are  useful  for  swimming  and  diving, sometimes  150 feet  deep,  to  collect  their  underwater  prey.

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The underwater brown kelp “seaweed forest”  is  a favorite   habitat  for  hunting  food.  Sea Otters not only find food in the underwater kelp “forests”, they protect the kelp – by eating Sea Urchins, because Sea Urchins can quickly decimate kelp forests if no Sea Otters are available to keep the Sea Urchin population in check.  Sea Otters also make use of kelp seaweed in another way – they wrap themselves in the seaweed, and become secured in place as if wearing a floating “seatbelt”, while they float in tidewater, asleep.  Securely tied to the anchored seaweed, the Sea Otters (who are “belted” in for a nap) will not be washed out to deep seawaters by the tides.

In other words, the relationship of Sea Otters to giant kelp (i.e., brown algae seaweed) is one of “mutual aid”, because both kelp and otter populations benefit from their interactions with each other. SeaOtter-seaweed-seatbelt.png

Where does the Sea Otter usually live? Its primary range covers the coastal tidewaters of Alaska’s Aleutian Islands archipelago chain, plus its south-central and southeastern coastlines, down the Canada’s British Columbia coasts, even to the Pacific coastline of the State of Washington.         ><> JJSJ


Dr. James J. S. Johnson’s background includes a love for animal ecology and the colder climates of the world. In addition to his (current) creation science education-focused work for ICR-SOBA, he has taught bioscience/ecology courses for Dallas Christian College and ACSI, written ecology-related curriculum for LeTourneau University, and served as lecturer aboard 9 international cruise ships, including 4 cruise ships  visiting  Alaska  (Norwegian Wind, Norwegian Sky,  Radiance of the Seas,  Rhapsody of the Seas).

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