photo source:Jimmy Hu http://www.silcom.com/~njhua/otter/ottertx1.html
In
progress 5/21/99
The Biogeography of the Sea Otter (Enhydra lutris)
by Tracy Benshoof, student in Geography 316
photo source:Jimmy Hu http://www.silcom.com/~njhua/otter/ottertx1.html
Species Name: Enhydra lutris
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Carnivora
Family:Mustelidae
Genus:Enhydra
Species:Enhydra lutris,
Description of Species:
According to Hu (1996),
there are three subspecies of Enhydra lutris. The Southern
sea otter is known as Enhydra lutris nereis, the Russian sea otter is Enhydra lutris
lutis the Alaskan sea otter
is Enhydra lutris kenyoni, and the Asian sea otter is Enhydra
lutris gracilis. While there are four subspecies, I will only
be talking about the Southern and Alaskan sea otters due to lack of information
on the other subspecies.
Sea Otters are about four feet long
and weigh an average of 65 pounds for males and 45 pounds for females.
They’ve got strong canines and strong molars to tear and crush their food.
Their lung capacity is 2.5 times the size of land mammals of the same size.
They have good eyesight and use their whiskers to sense vibrations in the
water. They’re known for the use of tools when eating. Because
they love mollusks, sea otters will use rocks as hammers and anvils to
help open the shells. Because they have no blubber, they must eat
25% of their body weight in food to maintain their high metabolism.
Grooming is important as it forces air bubbles into their fur that acts
as insulation (Friends of the Sea Otter).
Habitat:
Sea otters prefer the
temperate climate. They’re foragers who seek their food on the bottom
of rocky and soft-sediment subtidal habitats in coastal waters (VanBlaricom
& Estes 1988). They also make their home among the kelp forests.
Sea otters, in fact, help the kelp forests by eating the number one herbivore
in the region: sea urchins.
The original habitat of the sea otter
ranged from the Kurile Islands of Japan, to the Aleutian Chain of Alaska,
along the coasts of Washington and Oregon, and down the coast of
California to Baja California (Friends of the Sea Otter). There used
to be a continuous distribution of sea otters but their thick pelts made
them the favorite quarry of early fur traders in the 1700’s and 1800’s.
Also contributing to the demise of the sea otter is pollution.
Natural History:
Sea otters have extremely
thick fur. Estimates put the number of hairs per square inch at about
one million (Cohn 1998) while dogs only have about 60,000 hairs per square
inch. In the 18th century, otter fur was prized in the Russian, Chinese,
and Japanese courts (Woolfenden 1979). Land otters were hunted extensively
and became scarce. During an expedition to find a land passage between
Asia and North America, Vitus Bering discovered the Aleutian Islands and
Alaska. Stranded on an island on the way back to Russia, Bering and
some 30 others died. The survivors, among them a scientist named
Georg Wilhelm Steller, subsisted on sea otters and a sea cow until they
were able to build a new ship from the original, damaged ship. The
remaining members of the expedition would bring back to Russia 900 otter
pelts that would fetch a price of $30,000 (Woolfenden 1979).
Russian fur traders
quickly set out for the Aleutians and forced the aid of Aleut hunters.
Taking a cue from the Russians, the Spanish in California began to hunt
otters. According to Woolfenden (1979), in 1776, Captain James Cook
sailed the northwest coast of America, obtained otter furs cheaply and
sold them at high prices in Asia. Upon hearing this, European traders
also headed out to the North Pacific.
In 1812, the Russians established
Ft. Ross on the coast of Bodega Bay to be used as a center for their fur
trade operations in California and as agricultural land. According
to Essig (1933), by 1839, Ft. Ross was abandoned due to the dwindling numbers
of otters and the land was sold (Bailey puts the date of sale at 1841).
Bailey (1979) estimates that between 50,000 and 150,0000 otters were taken
by the Russians. After the Russians left, traders from other countries
came into the Bodega Bay area and resumed the killing of otters and took
thousands more (Bailey 1979).
In 1911, the International Fur
Seal Treaty saved the sea otters, as well as other marine mammals being
hunted for their pelts, from extinction. Under the 1972 Marine Mammal
Protection Act, sea otters have been listed as a "threatened" species in
1977. According to Cohn (1998), there were an estimated 150,000 sea
otters in Alaska and Aleutian Islands, 17,000-18,000 in Russia and northern
Japan, and 2200 in California, 1000 in British Columbia, and 500 in Washington
State. However, recent events have changed some of these numbers
dramatically.
Evolution:
Sea
otters are the smallest of marine mammal species. According to VanBlaricom
& Estes (1988), sea otters fall into two categories: those that eat
primarily fish and those that eat primarily invertebrates. The former
have evolved with sharp teeth for cutting and the latter have developed
strong molars for crushing their food. They also note that scientists
have traced the lineage of the modern sea otter back to an extinct species
called Enhydritherium that lived in the late Miocene in Europe and
North America.
Distribution:
Sea otters occupy much
of their historical range (VanBlaricom & Estes 1988). They are
found along the Kuril Islands off of Russia, the Aleutian Islands south
of the Bering Sea up to the southern coast of Alaska, and off the coast
of Central California. Their numbers have been reduced by heavy exploitation
in the 18th and 19th centuries for their pelts.
Sea otters are believed to have their
origins in the Old World and made their way to the New World (VanBlaricom
& Estes 1988). While the exact dispersal routes for the primitive
lutrinae aren’t known, there are theories as to what those possible paths
might have been. According to VanBlaricom and Estes (1988), some
suggestions include the sea otters using the Bering Land Bridge or the
North Atlantic to get to the New World. It’s also noted that the
species Enhydra lutris probably evolved in the North Pacific and
hasn’t dispersed since.
Maps of Distribution:
map source: Friends of the Sea Otter
map source: Friends of the Sea Otter
Other interesting issues:
A report
by the San Francisco Examiner (Kay 1999) states that the population
of Californian sea otters has declined beginning in 1995 (after a high
of 2,377 that year) at a rate of about 90 otters a year. If this
trend keeps up, the otters may become listed as "endangered". According
to a story by the San Francisco Chronicle, the 1998 population of
California sea otters numbered only 1,937 (McCabe 1999).
The Examiner report (1999)
lists as possible causes for the sharp decline in numbers infectious diseases,
contaminated waters, getting trapped in fishing equipment, starvation,
natural predators and speedboats. The report states that the National
Wildlife Health Lab has observed since 1992 that about 40 percent of dead
sea otters had carried diseases such as parasitic worms.
It’s been
10 years since the Exxon Valdez spilled nearly 11 million gallons of crude
oil into Prince William Sound. While the bald eagle and river otter
have recovered (Martin 1999), the Alaskan sea otter is still trying.
It’s estimated that about 800 Alaskan sea otters died as a result from
the oil spill.
According to Friends of the
Sea Otter, oil spills are the number one threat to sea otters. Otters
don’t have blubber like whales do. Instead, they get their insulation
from their thick fur. Constant grooming forces air bubbles into their
fur where it gets trapped and acts as insulation. Oil mats the fur
and if otters don’t have enough insulation, they’ll die of hypothermia.
Also, when the otter attempts to groom itself after a spill, the otter
will ingest the oil on its fur and get sick and/or die.
Another threat to the Alaskan
sea otter is the killer whale. A report by J. Estes et al. in the
journal Science (1998) points to increased killer whale predation
as the reason for the sharp decline in sea otter populations. According
to the article, an attack on a sea otter by a killer whale was first seen
in 1991 and since then there have been nine more. The possibility
that the otters died from starvation was ruled out as the urchin population,
the main diet of sea otters, is flourishing. Subsequently, kelp density
is also on the decline (the favorite food of sea urchins) (J. Estes et
al. 1998).
It is estimated in the report that a killer whale could
consume as many as 1,825 otters per year. That being the case, it
was concluded in the article that only 3.7 whales were necessary to cause
the otter population decline. Since whales and otters have existed
side by side for millennia, scientists believe that dwindling resources
of the whale’s natural prey are behind their sudden interest in eating
otters. Basically, less fish, less pinnipeds. With pinnipeds
on the decline, killer whales have turned to sea otters as a food source
(J. Estes et al. 1998).
There is some
hope for the sea otters. The Monterey Bay Aquarium has set up the
Sea Otter Research and Conservation Program. The main goal of this
program is to rescue and rehabilitate sea otter pups with the intent to
return them to the wild (Monterey Bay Aquarium 1999). They also aid
in rescuing sea otters from oil spills. Rescued sea otters will cleaned,
fed and groomed. Afterwards, they’ll be tagged with radio transmitters
so that scientists can continue to monitor them. According to the
Monterey Bay Aquarium’s website, over $450,000 is spent every year to support
the Sea Otter Research and Conservation Program.
One
controversial plan to save the sea otters is to have them relocated to
San Nicholas Island off the coast of Santa Barbara in the hopes of establishing
a population away from any potential oil spills that might occur in the
area in the future. Between 1987 and 1987, 139 otters were moved
to San Nicholas Island (Friends of the Sea Otters). At present, only
15 remain at the island. Some have died but others have returned
to their original "homes."
Bibliography
Bailey, Jane H. 1979. Sea Otter. Morro Bay California.
El Moro Publications.
E.O. Essig 1933. "The Russian Settlement at Ross" pp. 3-21. In the California Historical Society’s The Russians in California.
G.R. VanBlaricom and J.A. Estes, eds. 1988. The Community Ecology of Sea Otters. New York, NY. Springer-Verlag.
Wolfenden, John. 1979. The California Sea Otter: Saved or Doomed? Pacific Grove, CA. The Boxwood Press.
Journal or magazine articles:
Cohn, Jeffrey P. 1998. "Understanding Sea Otters" BioScience
48(3): 151-155.
J.A. Estes et al. 1998. "Killer Whale Predation on Sea Otters Linking Oceanic and Nearshore Ecosystems." Science 282 (16 October): 473-476
Kannan, Kurunthachalam et al. 1998 "Butyltin Resides in Southern Sea Otters (Enhydra lutris nereis) Found Dead along California Coastal waters." Environmental Science & Technology 32(9): 1169-1175.
Newspaper Articles:
Fernandez, Lisa, "Boaters on Slough Near Watsonville
Will Be Warned to Slow for Sea Otters," San Francisco Chronicle,
27 April, 1999, Sec. A. p. 20.
Kay, Jane, "Sea otters may be going down for 3rd time," San Francisco Examiner, 2 may, 1999, sec. C, p. 1.
Martin, Glen, "Valdez Spill Leaves Bitter Residue," San Francisco Chronicle, 24 March, 1999 Sec. A, p.1.
McCabe, Michael, "Otter Frustration," San Francisco Chronicle, 18, February 1999, sec. A, p. 15.
On-Line Sources:
Friends of the Sea Otter
http://www.seaotters.org
Jimmy Hu
http://www.silcom.com/~njhua/otter/ottertx1.html
Monterey Bay Aquarium
http://www.mbayaq.org/
http://www.discovery.com/stories/nature/otters/otters.html
send comments to bholzman@sfsu.edu
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