Distinguishing Oiled Pelage

It can sometimes be challenging to determine whether a sea otter has been oiled! Various other materials may be foul sea otter fur and this page describes how to distinguish between oil and other substances as well as how to collect oil samples.

Because sea otters live in seawater, their hair coat may come in contact with a variety of materials that can be confused with oil, including both man-made and natural substances. It is important to complete a careful inspection and, if there is any doubt, collect samples for confirmatory testing.

Can you name characteristics of an externally oiled otter?

  1. Strong petroleum smell
  2. Corneal, mouth and/or skin burns
  3. Material often easy to wipe off at the surface (unless groomed in, high concentration of volatile components, weathered, or tar)
  4. Matted hair coat, coat may appear wet and shiny and feel “greasy”, OR
  5. Coat may appear dry and lackluster (if exposed to petroleum product enriched with volatile compounds)
  6. Coat may be stained colorless to black, red, brown or yellow
  7. Similar material in the mouth, nose, eyes or digestive tract
  8. Variably-sized tar patties that are adherent to the fur
  9. IMPORTANT: If a non-oiled, dead otter washes up on a beach, tar patties may attach passively to the carcass. This must be distinguished from antemortem oiling. In this situation, the tar patties are often large, sand or debris-covered, loosely attached to the outer tips of the fur, and are easily removed with gentle pressure.
  10. Evidence of antemortem grooming of adherent, weathered tar patties:  Fragmentation of larger tar patties into small bits that are driven deep into the coat, forming small hair clumps with petroleum at the central core. The oil is typically attached deeper than the hair tips.
  11. Weathered oil and tar are often retained longest in areas that are the hardest to groom effectively (back of head, back, dorsal pelvis, tail)

Can you think of reasons why otters that have been exposed to a petroleum compound might be hard to detect from external examination alone?

  1. Some petroleum compounds are enriched for  volatile components , which evaporate quickly
  2. Weathered petroleum products may be firm or tarry and may not have a strong petroleum smell
  3. The otter may have groomed off the petroleum product
  4. A small area of fur could be affected: Sea otters are dependent on their fur coat for warmth, and a small amount of oil can cause significant impacts, especially if in contact with seawater

Can you name things that could be confused with petroleum contamination of a sea otter’s coat?

  1. Algae-Sea otters that have not been grooming enough will often have red algae growing on their fur. This usually indicates that a sea otter has been sick or has impaired mobility
  2. Algal compounds-Breakdown products of some marine algal blooms can act as surfactants (wetting agents), causing the fur or feathers to lose their ability to trap air and repel water
  3. Blood, diarrhea or melena-Hair that has become fouled with blood, feces or digested blood (melena) can easily be confused with oil exposure
  4. Mud-Otters that haul out in near sediment or mud can accumulate this material on their coat
  5. Non-petroleum oils, such as grease, fish oil, vegetable oil, surfactants and detergents- Although not petroleum, fouling of wildlife by these man-made compounds could represent pollution or “spill” events, and should be investigated
  6. Open wounds and infections- Wounds near areas of haired skin will often “weep” serum or pus.  This material can accumulate on adjacent fur and cause wetting of the coat.
  7. Poor coat care or pre-existing skin disease-Sea otters that are sick or have skin infections often have matted, wet coats and can look oiled

How might you be able to distinguish between the above substances and petroleum compounds on a sea otter’s fur coat?

  1. Algae-No petroleum smell, often red or red-brown, does not easily wipe off, growth often most dense on hair nearest the urethra (tail, back, pelvis), microscopic examination
  2. Algal compounds- Recent local history of algal bloom with abundant foam production, no petroleum smell, dries quickly to a yellow-green crust that is easily washed off with plain water
  3. Blood, diarrhea or melena- No petroleum smell, easily wipes off, fecal smell, often most dense on hair nearest the anus, positive for hemoglobin
  4. Mud- No petroleum smell, easily wipes off, most dense on portions of the coat in contact with the mud (legs, feet, ventrum)
  5. Non-petroleum oils, such as grease, fish oil, vegetable oil, surfactants and detergents- No petroleum smell, recent history of spill/ leakage or use, often affects multiple animals in a well-defined area, requires fingerprinting/ biochemical tests for identification
  6. Open wounds and infections- No petroleum smell, most apparent on hairs surrounding region of trauma, healing wound or abscess found
  7. Poor coat care or pre-existing skin disease- No petroleum smell, no dark color when the coat is wiped with a paper towel, when hair mats are pulled apart, no petroleum smell elicited, skin disease that does not appear to be oil-related, evidence of pre-existing illness

When sampling a live sea otter’s coat for petroleum testing:


  1. Shave the fur
  2. Collect a tiny sample (it’s best to get more than you think you’ll need)
  3. Collect samples without wearing PPE (eg gloves, Tyvek suit , respiratory protection, if indicated)
  4. Store the sample in a hot area, or area exposed to car exhaust or other petroleum compounds
  5. Store the samples near open flame
  6. Store the sample for a prolonged period prior to submitting it for testing


  1. Wear nitrile gloves and change them frequently while handling potentially oiled animals
  2. Collect an adequate sample size
  3. Label each sample with the spill name, animal species, animal number and collection date
  4. Store sample in appropriate container (Ideally a clean glass sample jar with a Teflon-lined lid)
  5. Maintain chain-of-custody and complete all required forms
  6. Submit sample for testing as soon as possible after collection
  7. Make sure that potential source material is also collected at the spill site