Sea Otters 'At Risk' From Low Genetic Diversity: 'This Is a Warning Sign, a Red Flag'

Scientists have warned sea otters have such a low level of genetic diversity that if their population were to decline, the species could be at risk of extinction.

Sea otters live in the shallow waters of the North Pacific Ocean and, before the 1700s, there were estimated to be between 150,000 to 300,000 worldwide. However, they were hunted to near extinction during the fur trade, with numbers plummeting to as few as 1,000.

In 1911, having realized the threat they were under, Russia, Japan, Great Britain and the U.S. signed the Treaty for the Preservation and Protection of Fur Seals. In the century since, sea otter numbers recovered, but the species is still listed as endangered—and its population is currently declining.

In a study published in the journal Molecular Biology and Evolution, researchers looked at the genetic diversity of sea otters. This is a measure of the differences between individuals within a given population. Large populations tend to have high diversity, while small ones—an endangered species, for example—tend to have low diversity.

Low genetic diversity means a species may be less likely to adapt to changing conditions. A species can lose genetic diversity when there is a sudden population crash—even if numbers recover, the diversity is lost. Cheetahs are an example of this—during the last ice age they almost went extinct.

In the latest research, led by Annabel Beichman from UCLA, scientists analyzed the genome of a sea otter from the Monterey Bay Aquarium. They then compared this to the genome of a South American giant otter. This species lives in a warm freshwater environment—far removed to the habitat of the sea otter.

sea otter
An Alaskan sea otter at a zoo in Japan. KAZUHIRO NOGI/AFP/Getty Images

Their findings showed sea otters have low genetic diversity, potentially harmful genetic variation and evidence of mating between closely related ancestors. "While low diversity isn't necessarily dangerous by itself, we also found elevated levels of potentially harmful variation within genes, possibly due to a history of population declines—which could impact the population going forward," Beichman said in a statement.

Study co-author Robert Wayne added: "Sea otters may be at risk. This is a warning sign, a red flag. We should make sure to not let their population decline again."

The team is now planning to analyze sea otters from other populations, including Japan, Alaska and the Aleutian Islands.

Sea otters are currently threatened by hunting and fishing, habitat disturbance, pollution from oil spills and climate change. Because of the vital role they play in the ecosystems they inhabit, they are known as a keystone species—without them, kelp forests and the animals that depend on them would also be at risk of disappearing.