ossible Effects of OCS Gas and Oil
Activities on the California Sea Otter
Sea otters are vulnerable to adverse impacts resulting from both routine gas and
oil activities on the outer continental shelf (OCS) and accidental events such as oil
spills. In California, sea otters live in nearshore waters from Año Nuevo south to the
Santa Maria River on the central coast, and at San Nicolas Island in the Southern
California Bight.
The California sea otter population, which numbered more then 2,000, was listed as
threatened under the Endangered Species Act in 1977. Routine offshore activities that
involve noise and physical disturbance may affect sea otters. These include geophysical
surveys, drilling, vessel and air traffic, and pipeline and platform construction and
abandonment.
Acoustical pulses, or sound waves, which are used in seismic reflection surveys, are
generated by airguns or waterguns. These have not been shown to affect sea otter behavior,
even when the pulses have occurred less than one mile away. In California, sea otters
rarely move more than 1 mile from shore, while OCS activities generally occur 3 miles or
more from shore. Given their occurrence close to shore and the evidence that sea otters
may not be sensitive to this type of noise, it is unlikely that seismic surveys would have
an effect on the population.
There is no information on the potential impacts on sea otters from exploratory and
development drilling or platform and subsea pipeline construction. One study, however,
observed sea otters in the presence of drillship and production platform sounds and
reported no changes in behavior at distances as close as a kilometer from the source. The
otters continued to dive and feed during the playbacks.
Although there have been no systematic studies of the reactions of sea otters to
aircraft, sea otters exhibited no obvious reactions to a two-engine survey aircraft during
a series of aerial surveys of the California sea otter range conducted at an altitude of
about 300 feet. No sea otter reactions were observed during one study using playbacks of
helicopter noise.
Sea otters often allow close approaches by boats, but tend to avoid heavily disturbed
areas. They do, however, reoccupy those areas in times of less traffic. Accidental
collisions between sea otters and support-base boat traffic are unlikely, because of the
otters' mobility, their nearshore distribution, and the distance between their range and
gas and oil support bases in the Santa Barbara Channel.
Accidental oil spills have a greater negative effect, however. Sea otters must maintain
a layer of warm, dry air in their dense underfur to insulate against the cold; they are
the marine mammals most sensitive to the effects of oil contamination. Even partial
fouling of 30 percent of an otter's body surface could result in death.
In 1989, during the Exxon Valdez oil spill in Alaska, many sea otters did not avoid
oiled waters and were fouled. More than 1,000 dead sea otters were recovered, and another
350 oiled otters were rescued and taken to treatment centers for rehabilitation. Four
critical factors were identified in the sea otter mortality during the spill in Alaska:
pulmonary emphysema, caused by the inhalation of toxic fumes, occurred primarily during
the first 2 weeks of the spill; low body temperature, or hypothermia, was a direct result
of oil contamination of the fur, which decreased insulation; low blood sugar, or
hypoglycemia, was probably caused by poor gastrointestinal function due to ingestion of
oil; and lesions in other organs, including the liver, heart, spleen, kidney, and brain,
were also probably caused by ingestion of oil and by stress. Oil spills can also affect
sea otters indirectly by reducing available food resources, either killing prey organisms
or making them unpalatable. Sea otter habitat can also be lost temporarily if kelp forest
communities become contaminated.
If an oil spill comes in contact with nearshore waters inhabited by sea otters, it is
likely that some otters will die. The magnitude of sea otter mortality would vary with a
number of factors. Time of year, volume of oil spilled, and winds and currents all
contribute, as do the distance of the spill from shore. The volume and condition of oil
contacting the shoreline, the success of containment operations, and the effectiveness of
otter cleaning and rehabilitation are also significant factors.Because of the variety of
factors involved, the range of possible impacts to the sea otter population is wide. Over
time, spilled oil is weathered--hardened and rendered less toxic by exposure to the
elements. A highly weathered spill might contact the shoreline and not affect the sea
otter population at all. At the other extreme, a spill occurring close to shore within the
sea otter range could oil and kill hundreds of animals.
There are reasons for optimism, however. As a result of preventive measures taken by
the MMS and industry on the OCS, including stringent regulations, inspections, and safe
operating procedures, there have been no large offshore oil spills in the Pacific Region
since 1969. Additionally, California Senate Bill 2040, enacted in 1990, provides for the
construction of a permanent facility to clean and rehabilitate oiled sea otters, and for
the development of a statewide program to address the needs of all oiled wildlife. The sea
otter facility, which will be located at U.C. Santa Cruz's Long Marine Laboratory on
Monterey Bay, is scheduled to be operational in 1994. Once this facility and the program
are in place, the California sea otter population will be better protected from the
effects of oil spills. Oil tankers heading south from Alaska are now voluntarily rerouted
50 miles or more off the coast along the sea otter range, with the expectation of further
reducing the chances of a spill affecting this population.
Selected Readings
Bonnell, M.L., and M.D. Dailey. 1993. Marine mammals of the Southern California Bight.
Pp. 604-681, in, M.D. Dailey, D.J. Reish, and J.W. Anderson (eds.), Ecology of the
Southern California Bight: A Synthesis and Interpretation. University of California Press,
Berkeley/Los Angeles
Geraci, J.R., and D.J. St. Aubin (eds.). 1990. Sea mammals and oil: confronting the
risks. Academic Press, Inc., San Diego. 282 pp.
Orr, R.T., and R.C. Helm. 1989. Marine Mammals of California. California Natural
History Guides: 29. University of California Press, Berkeley. 93 pp.
Riedman, M.L., and J.A. Estes. 1990. The sea otter (Enhydra lutris): behavior, ecology,
and natural history. U.S. Department of the Interior, Fish and Wildlife Service,
Washington, D.C. Biological Report 90(14). 126 pp.
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