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 Although only a
small percentage of oil enters the ocean from major oil spills, it is from
studies during those events that we understand the extreme toxicity oil has
on marine animals. A smaller spill at the wrong time/wrong season and in a
sensitive environment may prove much more harmful than a larger spill at
another time of the year in another or even the same environment. Even small
spills can have very large effects. Thus, one should not merely compare
figures — the size of an oil spill is certainly not the only factor of
importance in terms of what environmental damage can be caused by the oil.
In 1976, a spill estimated to have been less than 10 tons killed more than
60,000 long-tailed ducks wintering in the Baltic Sea and attracted to the
seemingly calm water surface created by the oil slick. This could be
compared to the effects on seabirds in Alaskan waters from the approximately
40,000 tons of the larger Exxon Valdez oil spill in 1989, when an
estimated 250,000 birds died.
As
summarized by the Australian Maritime Safety Authority, important factors
related to the impact of an oil spill on wildlife are:
-
The
spread of the oil slick
-
The type
of oil spilled, its movement and weathering characteristics
-
The
location of the spill
-
The
area of estuary, sea and foreshore impacted by oil
-
The
sensitivity of the regional environment, e.g. proximity to bird breeding
colony
-
The
number of different habitats impacted, such as rock shore, beach,
mangrove, wetland
-
The
timing of the incident (during seasonal breeding, bird migration)
-
The
nature, toxicity and persistence of the oil
-
The
variety of species at the spill location
 Oil may kill
seabirds in several ways. The first effect is often that oil destroys the
structure of its protective layer of feathers and insulating down. The fat
under the birds skin is an energy reserve as well as an extra layer of
insulation. Cold water quickly penetrates into the down and reaches the
skin. The amount of oil that a bird is smeared with is not important. In a
cold climate an oil spot the size of 2-3 sq. centimetre can be enough to
kill a bird. The insulating effect of the plumage is destroyed by the oil,
and the bird freezes to death (hypothermia). If a bird gets smeared with a
lot of oil it may clog the bird's feathers making it impossible for it to
fly. The bird may also loose it buoyancy (its ability to float on the water
surface) and actually drown. In their efforts to clean themselves from oil
and put their feathers in their original state, the birds may inhale or
ingest oil. As many of the substances in oil are toxic, this may result in
serious injuries/health effects such as pneumonia, congested lungs,
intestinal or lung hemorrhage, liver and kidney damage. This poisoning is
often as deadly as hypothermia, although the effects may not manifest
themselves as quickly. Oil may also affect the reproductive success of the
birds as oil from feathers of a bird that is laying on eggs may pass through
the pores in the eggshells and either kill the embryos or lead to
malformations.
Seals are
very vulnerable to oil pollution because they spend much of their time on or
near the surface of the water. They need to surface to breathe, and
regularly haul out onto beaches. During the course of an oil pollution
incident, they are at risk both when surfacing and when hauling out. Fur
seals are more vulnerable due to the likelihood of oil adhering to their fur
which will result in the fur losing its insulating ability (as they lack any
blubber for additional insulation). Heavy oil coating on fur seals may
result in reduced swimming ability and lack of mobility when the seals are
on land. Seals could also be damaged through the ingestion of oiled food or
the inhalation of oil droplets and vapors. Oil, especially light oils and
hydrocarbon vapors, will attack exposed sensitive tissues. These include
mucous membranes that surround the eyes and line the oral cavity,
respiratory surfaces, anal and urogenital orifices. This can cause corneal
abrasions, conjunctivities and ulcers. Consumption of oil-contaminated prey
could lead to the accumulation of hydrocarbons in tissues and organs.
 Sea otters
spend a lot of their time on the sea surface and are totally depending on
their fur for isolation and for the ability to float. As a consequence, sea
otters are regarded as being very sensitive to oil spills as oil may result
in the fur losing its capacity to insulate the animals. However, inhaling
hydrocarbons or ingesting oil when they groom themselves can damage their
lungs, cause ulcers, and result in liver and kidney damage. Habitat loss and
diminishing food resources constitute indirect effects on the otters. The
Exxon Valdez incident is believed to have led to the death of 15,000
otters, mainly as a result of ingestion of oil.
Polar
bears are depending on blubber, so called guard hair and a thick underfur
for insulation. When grooming an oil contaminated fur they may swallow oil,
something that is known to have resulted in the death of polar bears. There
is also some evidence that the toxic effects of oil cause an inability of
polar bears to produce red blood cells and lead to kidney damage.
Due to
their migratory behaviour, there is little documented evidence of cetaceans
(whales) being affected by oil spills. It would, however seem likely that
baleen whales would be particularly vulnerable to oil while feeding. Oil may
stick to the baleens while the whales "filter feed" in the vicinity of oil
slicks. They plunge, take in huge quantities of water and then filter out
their feed of plankton and krill. Sticky, tar-like residues are then
particularly likely to foul their baleen plates. There are also indications
that whales can inhale droplets of oil, vapors and fumes if they surface in
slicks when they need to breathe. Exposure to oil in this way could lead to
damage of mucous membranes, injuries in airways or even cause death.
Dolphins are smooth-skinned, hairless mammals, and as a consequence oil
tends not to stick to their skin, but they can inhale oil and oil vapor.
This is most likely to occur when they surface to breathe. This may lead to
damages of the airway and lungs, mucous membrane damage or even death. A
stressed or panicking dolphin would move faster, breathe more rapidly and
therefore surface more frequently into oil which would increase exposure.
Dolphins eyesight may also be affected by oil.
Exxon
Valdez
oil spill research has revealed unexpected persistence of toxic subsurface
oil and chronic exposures. Even at sublethal levels, the 14 year old oil has
continued to affect wildlife. Delayed population reductions and cascades of
indirect effects has postponed recovery (see:
http://www.afsc.noaa.gov/Publications/misc_pdf/peterson.pdf)
Read about
the Conservation Science Institute
executive director's
and
science director's
work on the Exxon Valdez oil spill. |
|
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