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| From Wikipedia |
The small square of fur was silky smooth and buttery soft. The surface hairs were deep brown, long and supple. Underneath, short fuzzy hairs cushioned my hand as it rested on the fur. It was 2004, I was at the Monterey Bay Aquarium, and I was petting a piece of sea otter fur.
Why is sea otter fur so remarkable?
Sea otters spend about 10% of their day grooming their fur, keeping it clean and blowing air into it to maintain this insulating layer. Oil spills are more devastating to sea otters than to other marine mammals because oil collapses the animal's fur and allows cold water and warm otter to meet, leading to hypothermia and death.
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| Click to enlarge From alaska.fws.gov |
Sea otter fur keeps people warm just as well as it keeps a sea otter warm. Hunters seeking sea otter pelts swept through otter populations in the 18th and 19th centuries. Otter populations fell from more than 200,000 animals, distributed along the Pacific Coast between Alaska and Mexico, to a handful of populations sprinkled along remote shorelines in Alaska.
Hunting slowed as sea otter populations declined -- it became harder and harder to make money in the fur business. The disappearance of the sea otter was noticed by more than hunters. A 1911 international treaty between the US, Russia, Great Britain, and Japan placed sea otters and Northern fur seals off-limits for hunting. Local laws provided further protection, like the California state law that made the sea otter a "fully protected mammal". In 1913, when this law passed, it appeared that there weren't any sea otters available for such protection in California state waters.
As with other near-extinction stories, protections came late and the damage to coastal environments was already done. The loss of the sea otter had widespread devastating effects on near-shore habitats of the northern Pacific.
Sea Otters as Keystone Species
Sea otters generally call kelp forests home, spending 70% of their time among the large brown algae. Kelp forests are restricted to relatively shallow waters with flat rocky bottoms, to which the kelp "plant" can attach. The "plant" -- called a thallus -- grows rapidly toward the surface of the water, converting the two-dimensional ocean floor into a complex three-dimensional forest. Increasing the structural complexity of the environment creates lots of places for other organisms to live, including fish, invertebrates, and other kinds of algae. Indeed, kelp forests are some of the most diverse and productive marine environments on earth.
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| Photo: California Academy of Sciences |
One invertebrate group in particular, the sea urchins, are also important in the ecology of kelp forests. Sea urchins eat kelp by scraping away the kelp holdfast. The holdfast keeps the thallus anchored in place, so losing it releases the kelp and it washes away in ocean waves. When sea urchins become abundant, they swarm over the kelp and clear entire areas of the algae. When the kelp is gone, the urchins switch to other kinds of algae or move to new locations with better feeding.
A sea otter, however, loves to eat sea urchins. And it is always hungry. A fifty-pound sea otter must eat about seventeen pounds of food every day, including clams, abalone, and sea urchins, to keep its metabolic furnaces stoked. Seventeen pounds of food for a fifty pound animal. Think about that. It's like a 160 pound man eating twelve 16-oz T-bone steaks at breakfast, lunch, and dinner. Every day...
Because of their voracious appetite for urchins, sea otters keep urchin populations in check, saving kelp from the spiny hordes. Areas without sea otters tend to have a lot of urchins -- but not much kelp. In the few places where sea otters persist, kelp forests thrive. By reducing grazing by urchins, sea otters promote healthy kelp ecosystems and indirectly support the biodiversity of kelp forests. In fact, researchers don't have to count sea otters to know if their populations are healthy -- they can just look at the extent of the kelp forest.
Species with this kind of disproportionate effect on diversity are considered keystone species. Like the keystone in an arch supports a building, a keystone species in ecology supports an ecosystem. Without the keystone, the whole ecosystem is lost.
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| Click to enlarge From alaska.fws.gov |
What about places where the sea otter disappeared? By the end of the fur hunting era, otters were restricted to isolated populations in Alaska -- on the outer Aleutian Islands, the Alaska peninsula, and Commander and Kurile Islands. In addition, one small population persisted in Northern California, near Bixby Point.
But Lori, you say, those sea otters are in Northern California and the Channel Islands are in Southern California. Why are you writing about sea otters on a Channel Islands blog?
Sea otters are important for the Channel Islands, both historically and in the present. Ships carrying otter hunters traveled through the Southern California Bight searching for otter populations, changing the lives of the people they met and the ecosystems they exploited. Efforts by the US Fish and Wildlife Service in the 1980s to reintroduce the California sea otter to the Southern California Bight were met with anger and distrust by fishermen -- and set the stage for a sea otter mini-recovery south of Point Conception on the island of San Nicolas.
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| From Wikipedia |
Stay tuned for more drama surrounding the loss and recovery of the sea otter in and around the Channel Islands...
References:
Allen, S. G., J. Mortenson, and S. Webb. 2011. Field Guide to Marine Mammals of the Pacific Coast. California Natural History Guides Series No. 100. University of California Press: Berkeley, CA.
Riedman, M. L. and J. A. Estes. 1990. The sea otter (Enhydra lutris): Behavior, Ecology, and Natural History. Biological Report 90 (14). United States Fish and Wildlife Service, Department of the Interior.
Photo credits:
Sea otter and urchin photo from the California Academy of Sciences webpage (http://www.calacademy.org/science_now/archive/wild_lives/urchin.php)
Sea otter range maps from USFWS Alaska Region website
Wikipedia photos from the sea otter Wikipedia entry
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