The external effects of oil on marine mammals including sea otters, sea lions, seals, walruses, sea cows or manatees, dolphins, porpoises and whales, will depend on the species but may include:

• Hypothermia in fur seal pups by reducing or destroying the insulation of their woolly fur. Adult fur seals have blubber and would not suffer from hypothermia if oiled. Dolphins and whales do not have fur, so oil will not easily stick to them.
• Marine mammals such as fur seals become easy prey if oil sticks their flippers to their bodies, making it hard for them to escape predators; fur seal pups can drown if oil sticks to their flippers.
• Marine mammals lose body weight when they cannot feed due to contamination of their environment by oil.
• The scent that seal pups and mothers rely on to identify each other is disguised, leading to rejection, abandonment and starvation of seal pups.
• Inflammation or infection in manatees and difficulty eating due to oil sticking to the sensory hairs around their mouths.

The internal effects include:

• Poisoning and toxic effects due to ingestion of oil
• Congestion of lungs and damaged airways
• Gastrointestinal ulceration and haemorrhaging.