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The U.S. Fish and Wildlife Serviceis the federal agency responsible for many of the nation’s sh and wildliferesources. Having this responsibilityhas established the agency as one of theprimary trustees for sh, wildlife andhabitat at oil spills.

Oil spills affect wildlife and their

habitats in many ways. The severityof the injury depends on the type and

quantity of oil spilled, the season andweather, the type of shoreline, and the

type of waves and tidal energy in thearea of the spill.

Oil can be categorized into ve groups,

ranging from very light to very heavyoils. Most oil has a density less thanwater, so it oats. Oil tends to spread

into a thin layer on the water surface asa sheen. Once in the water, oil undergoes

weathering, a process that describesthe physical, chemical, and biological

changes that occur when oil interactswith the environment.

Weathering reduces the more toxic

elements in oil products over time, asexposure to air, sunlight, wave andtidal action, and certain mircoscopic

organisms degrades and/or dispersesoil. Weathering rates depend on

factors such as type of oil, weather,temperature, and the type of shoreline

and bottom that occur in the spill area.

Types of Oil Very light oils (jet fuel, gasoline) are

highly volatile and evaporate quickly.Very light oils are one of the most

acutely toxic oils and generally affect

aquatic life (sh, invertebrates, and

plants) that live in the upper water

column.

Light oils (diesel, light crude, heating

oils) are moderately volatile and canleave a residue of up to one third of the

amount spilled after several days. Lightoils leave a lm on intertidal resources

and have the potential to cause long-term contamination.

Medium oils (most crude oils) are less

likely to mix with water and can causesevere and long-term contamination to

intertidal areas. Medium oils can also

severely impact waterfowl and fur-bearing marine mammals.

Heavy oils (heavy crude, No. 6 fuel oiland Bunker C) do not readily mix with

water and have far less evaporationand dilution potential. These oils tendto weather slowly. Heavy oil can cause

severe long-term contamination of intertidal areas and sediments. Heavy

oils have severe impacts on waterfowland fur-bearing marine mammals.

Cleanup of heavy oil is difcult and

usually long-term.

Very heavy oils can oat, mix, sink, or

hang in the water. These oils can beco

oil drops and mix in the water, oraccumulate on the bottom, or mix withsediment and then sink.

Wildlife and HabitatOil causes harm to wildlife throughphysical contact, ingestion, inhalationand absorption. Floating oil can

contaminate plankton, which includesalgae, sh eggs, and the larvae of 

various invertebrates. Fish that feedon these organisms can subsequently

become contaminated. Larger animals

in the food chain, including biggersh, birds, terrestrial mammals, and

even humans may then consumecontaminated organisms.

Initially, oil has the greatest impacts o

species that utilize the water surface,such as waterfowl and sea otters, and

species that inhabit the nearshoreenvironment. Although oil causes

immediate effects throughout the entispill site, it is the external effects of oon larger wildlife species that are ofte

immediately apparent.

Plants

Marine algae and seaweed responds

variably to oil, and oil spills may resulin die-offs for some species. Algae

may die or become more abundant inresponse to oil spills. Although oil can

prevent the germination and growthof marine plants, most vegetation,including kelp, appears to recover afte

cleanup.

Effects of Oil Spills on Wildlife and Habitat

 Alaska Region

Pool of oil on a heavily impactedbeach, Prince William Sound, AK.NOAA

Sediment plume and sheens of  reoated oil, Prince William

Sound, AK. NOAA

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sensitive to oil toxins.

Birds and Mammals

Physical contact with oil destroys theinsulation value of fur and feathers,

causing birds and fur-bearing mammalsto die of hypothermia. In cold climates,

an inch diameter oil drop can be enoughto kill a bird. Heavily oiled birds can

loose their ability to y and theirbuoyancy, causing drowning.

In efforts to clean themselves, birds

and sea otters ingest and inhale oil.Ingestion can kill animals immediately,but more often results in lung, liver, and

kidney damage and subsequent death.Seals and sea lions may be exposed to

oil while breathing or resting at thewater’s surface or through feeding on

contaminated species.

Long-term or chronic effects onbirds and marine mammals are less

understood, but oil ingestion has beenshown to cause suppression to theimmune system, organ damage, skin

irritation and ulceration, damage to theadrenal system, and behavioral changes.

Damage to the immune system canlead to secondary infections that cause

death and behavioral changes may affectan individual’s ability to nd food or

avoid predators. Oil also affects animalsin non-lethal ways such as impairingreproduction.

Avian and mammalian scavengerssuch as ravens, bald eagles, and arcticfoxes are also exposed to oil by feeding

on carcasses of contaminated sh andwildlife. Direct mortality and reduced

reproduction in bald eagles were

attributed to the Exxon Valdez oil spi

Habitat

Oil has the potential to persist in theenvironment long after a spill event a

has been detected in sediment 30 yearafter a spill. Oil spills may cause shift

population structure, species abundanand diversity, and distribution. Habit

loss and the loss of prey items also hathe potential to affect sh and wildlifepopulations.

Oil remains in the environment long

after a spill event, especially in areassheltered from weathering processes,

such as the subsurface sedimentsunder gravel shorelines, and in somesoft substrates. However, pelagic and

offshore communities are fairly resilieand rebound more quickly than inshor

habitats. Although oil is still present

in the sediment and coastal areas 15years after the Exxon Valdez oil spillin Prince William Sound, Alaska, somwildlife populations have recovered. I

is believed that continued effects willmost likely be restricted to population

that reside or feed in isolated areas thcontain oil.

The U.S. Fish and Wildlife Service

responds to spills to minimize impactsto trust resources and continues its

work long after a spill event. The

Service continues assess and monitorthe damage to habitat and wildlife and

attempts to minimize the long-termeffects on new generations of wildlife

U.S. Fish & Wildlife Service1 800/344 WILDhttp://www.fws.gov

For more information, contact:U.S. Fish and Wildlife Service

Regional Spill Response Coordinator1011 E. Tudor Road Anchorage, Alaska 99503

907/786 3598

Visit the Contaminant Program home paghttp://alaska.fws.gov/sheries/ 

contaminants/index.htm

December 2004

Oily sheen in the intertidal habitat with aquatic plants following theExxon Valdez spill.

Oiled loon, Prince William Sound, AK.

Invertebrates

Oil can be directly toxic to marineinvertebrates or impact them throughphysical smothering, altering metabolic

and feeding rates, and altering shellformation. These toxic effects can be

both acute (lethal) and chronic (sub-lethal). Intertidal benthic (bottom

dwelling) invertebrates may beespecially vulnerable when oil becomeshighly concentrated along the shoreline.

Additionally, sediments can becomereservoirs for the spilled petroleum.

Some benthic invertebrates can surviveexposure, but may accumulate high

levels of contaminants in their bodiesthat can be passed on to predators.

Fish

Fish can be impacted directly throughuptake by the gills, ingestion of oil oroiled prey, effects on eggs and larval

survival, or changes in the ecosystemthat support the sh. Adult sh may

experience reduced growth, enlargedlivers, changes in heart and respiration

rates, n erosion, and reproductiveimpairment when exposed to oil. Oilhas the potential to impact spawning

success, as eggs and larvae of many shspecies, including salmon, are highly

Oiled sea otter, Prince William sound AK  USFWS