The harmful impact of oil on sea otter pelts leads to their demise
When oil from offshore drilling sites contaminates the ocean, it poses a risk to sea otters. Researchers from the United States conduct studies on deceased sea otter furs and discover disturbing findings. They discover that oil in the fur of these animals decreases buoyancy by roughly 55%, making it challenging for them to float. Even after washing, the original buoyancy cannot be fully restored, as stated in the journal "Journal of Experimental Biology".
California sea otters, specifically (Enhydra lutris nereis), spend the majority of their time in the sea where they float on the surface to rest, feed, or groom themselves. Their dense, waterproof fur gives them exceptional buoyancy, as researchers including Kate Riordan of California Polytechnic State University San Luis Obispo explain.
Dense fur for warmth and buoyancy
As the only marine mammal, sea otters do not have a thick layer of blubber. Instead, they rely on their thick, waterproof fur to stay warm and their high metabolism. A sea otter must consume 20-30% of its body weight in food daily to meet its energy needs, and even hunting requires a lot of energy due to their high buoyancy and inefficient swimming style.
US Fish and Wildlife Service describes that sea otter fur contaminated with oily substances can lead to their death due to ruined insulating properties and hypothermia. Riordan's team wanted to investigate the extent to which oil further compromises the animals' buoyancy in water.
The researchers received 37 fur samples from deceased sea otters from a Californian agency. These fur samples were tested under three conditions: untreated, oiled, and washed with detergent.
The furs were taken from newborns (under one month), small pups (one to two months old), large pups (three to five months old), juveniles (six months to one year old), adults (one to three years old), and older adults (four to nine years old).
The fur buoyancy force was measured in N. Untreated furs with a 25 square centimeter size had a buoyancy force of approximately 0.3 N, whereas oiled furs had only 0.145 N, about 55% less. After washing, the buoyancy force improved, but it still remained just over 40% less than the original fur (about 0.197 N).
Young otters have different buoyancy
Researchers paid particular attention to the fur of very young sea otters, whose fluffy fur has long been suspected to provide even more buoyancy than that of adult animals. "The buoyancy of the birth fur of sea otters had never been measured empirically."
In the experiment, all fur pieces provided comparable buoyancy, regardless of the age of the animals, likely because an equal amount of air was trapped everywhere, as researchers think. However, they observed differences between age classes when calculating the buoyancy force per entire animal and considering body size. Smaller animals have a relatively larger surface area, so young animals have proportionally more fur and thus more buoyancy – almost twice as much.
Oil in fur has the greatest effect on pups
"It's stated in the study that a pup must swim alone at the water surface when the mother goes on short hunting trips, in which case, the pup's buoyancy is particularly important." Around five weeks, young sea otters attempt to dive, but it's not successful until around ten weeks. If a pup's fur is contaminated with oil, the change in buoyancy is particularly significant.
The authors note that they only examined fur in the lab and not how much buoyancy live otters actually have. It could also be that the animals can restore their fur's full functionality through grooming after the oil is washed off.
An oil spill, such as an oil spill off California's coast, is currently the greatest human-induced threat to sea otters, explains lead author Riordan. However, if there's an oil spill, numerous organizations and thousands of volunteers know how to help the wildlife.
Researchers, inspired by the impact of oil on sea otter buoyancy, decided to investigate how oil contamination affects the buoyancy of sea otter fur in different age classes. They found that oil significantly reduces the buoyancy of sea otter fur, with a 55% decrease in buoyancy force for oiled furs compared to untreated furs. Moreover, the study revealed that young otters, particularly pups, are more susceptible to the effects of oil on their buoyancy.
