While scientists are
searching for all the reasons behind the decline of the California sea
otter, there is no question that disease is one cause. Starting in 1998,
disease has contributed to about 40 percent of the number of sea otter
deaths each year. This is an unprecedented figure for any wildlife
population.
Some
of the diseases observed in the California sea otter population include
fatal infections from acanthocephalan worms (intestinal in nature); a
variety of bacterial infections; protozoal encephalitis (infection of
the brain); and a fungal infection, coccidioidomycosis or San Joaquin
Valley fever.
What is causing this increase in diseases? Is it worsening pollution
in the Monterey Bay ecosystem, as well as other portions of the
California coast? Scientists are grappling with these questions in an
effort to save sea otters.
In a heavily agricultural area such as Monterey Bay, organochlorine
compounds, some of the
breakdown products of formerly used pesticides such as DDT, still
persist in the environment and enter into the marine ecosystem in
run-off. Other currently used pesticides may pose serious threats to sea
otters. The organochlorine compounds build up, or bioaccumulate, in the
organs of sea otters’ prey such as mussels, clams and other shellfish.
When sea otters eat these shellfish, the deadly chemicals concentrate in
their systems, and that sometimes results in debilitation and
reproductive failure. Shellfish appear on restaurant menus, so the
bioaccumulation of chemicals in marine invertebrates could potentially
become harmful to humans.
In addition to agricultural run-off, pollution such as
polychlorinated biphenyl (otherwise known as PCBs) and heavy metals
enter into the marine ecosystem through storm sewer discharge and
industrial discharge.
Tributyltin, from boat paints, can
enter into the marine ecosystem from marina-related activities.
Scientists have found that sea otters, from certain areas of Monterey
Bay, that were afflicted with infectious diseases contained a greater
concentration of tributyltin in their tissues than those sea otters that
died from trauma and other unknown causes. Tributyltin has been well
documented as causing immune suppression in other mammals and fish. It
is possible that tributyltin and other pollutants found in the waters in
Monterey Bay are making sea otters vulnerable to infectious diseases.
Even something as seemingly innocuous as cat litter may hurt sea
otters. Toxoplasma gondii, one of the species that causes
protozoal encephalitis in sea otters, is associated with the house cat.
One of the theories as to how this organism is showing up in sea otters
is through the improper disposal of flushable cat litter.
Finally, there is oil pollution -- the No. 1 threat to sea otters.
Oil pollution can cause hypothermia and organ damage in sea otters. When
their fur becomes matted by oil, the insulation is impaired. Sea otters
can’t maintain heat and they die from exposure.
Their organs can become damaged when they ingest oil by grooming
their fur.
