TOP SECRET SUCCESS STORY: conspiracy saved sea otters

Sea otters in the wild. Photo credit: Dave Bezaire & Susi Havens-Bezaire.
Sea otters in the wild. Photo credit: Dave Bezaire & Susi Havens-Bezaire.

By Stacey Venzel

The unheralded discovery of a colony of California sea otters in 1915 and the surprising way biologists handled the situation just may the best-kept secret in marine biology history.

Skins of sea otters in 1892. Photo credit: NOAA.
Skins of sea otters in 1892. Photo credit: NOAA.

Due primarily to the booming otter fur trade of the 19th century, the California sea otter population was believed to be extinct by the start of the 1900s, according to the United States Geological Survey. But in 1915, a team of biologists encountered a population of 32 individuals, alive and thriving in a Big Sur cove 30 miles south of Monterey Bay. To protect the population from further exploitation, the biologists told no one.

Amazingly, their secret lasted for more than 20 years. The clandestine sea otter colony didn’t become public knowledge until 1938 when the construction of a major highway brought the hidden region into plain view. By then, the population had grown to approximately 50 otters. The 2014 U.S.G.S. census of California sea otters calculated that the population was just below 3,000, each one a descendant of the undisclosed Big Sur population.

Considering that sharing new discoveries with the public is the goal of most scientists, the decades-long secret maintained by a small group of biologists was a stunning success as well as highly unusual.


The California sea otter, also referred to as the Southern sea otter, is one of three subspecies. The Alaskan and Russian populations that inhabit colder climates once faced extinction, too. Sea otters are protected in U.S. waters under the Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973. Both the Alaskan and California sea otters are listed on the International Union for Conservation of Nature’s Red List as threatened. Though concern for the species’ survival due to hunting them for their fur coat is mostly a thing of the past, it appears that all populations are still recovering from the catastrophic effects of the extensive sea otter hunts more than a century ago.

Map of sea otter populations. Photo credit: Christophe Cagé.
Map of sea otter populations. Photo credit: Christophe Cagé.

Between the late 1700s and late 1800s, the trade decimated otter populations in Russian and Alaskan habitats, forcing trappers to move further south to California.

With the densest hair of any mammal, the sea otter boasts an impressive pelt, one that was a coveted possession for polar climate dwellers. A sea otter has up to one million hairs per square inch on its body, giving these furry swimmers a natural jacket of warmth. (To help put that in perspective, the average human head has a total of 100,000 hairs.) The sea otter fur trade only ended when the species was believed to have vanished. Enactment of the 1911 International Fur Seal Trade Act was too late to protect the obliterated sea otter population, except for the colony of 32 otters discovered in Big Sur.

Today, southern otter population trends are not as promising as scientists would hope, even though hunting them is still illegal. In California, the only known natural predator for sea otters is the great white shark; but deaths caused by shark attacks appear to be primarily from exploratory bites by great whites sharks, not outright predation by the sharks. Great whites feed on blubbery animals but are believed to occasionally mistake sea otters for a sea lion meal. When the sharks determine that the sea otters just aren’t plump enough, they abandon the kill, leaving the body to become a statistic that washes ashore.

But if predators are not making a noticeable dent in the numbers, why is the sea otter struggling to make a comeback?


Incidental bycatch and food shortage have dealt a hand in the animal’s decline. Genetics also might be playing a role. In a recent study, 18th– and 19th-century sea otter populations showed a wider genetic variation than current populations. These findings are not surprising considering the 21st century’s ancestry can all be traced back to the sea otters found in Big Sur. The implications of such facts are troubling. Low genetic diversity puts an already vulnerable species at elevated risks of successful reproduction and subsequent survival. Reduced biological fitness also makes these animals more susceptible to disease.

The U.S.G.S. reports that because of their habitat range’s close proximity to shore, sea otters are more readily affected by runoff, pathogens and pollution than marine life living far off the bank. This makes them an indicator species, which means when diseases start appearing in sea otter populations, we should look to our coasts for possible answers. Studies by the U.S.G.S. have found that sea otters display adverse effects to fire ash pollution from wildfires and can die from exposure to microcystin, a fertilizer toxin responsible for green-colored algal blooms.

In addition to being an indicator species, sea otters are vital to the marine ecosystem in other ways as well.

“They are uniquely capable of limiting herbivorous invertebrates like sea urchins that, if left unchecked, can decimate kelp beds and the fish habitat they provid,” said U.S.G.S biologist Tim Tinker, underscoring the importance of strong otter populations.

The Otter Project points out that sea otters are also an umbrella species, meaning that protecting them tangentially safeguards a myriad of other species that share the same ecosystem.

If researchers had revealed their discovery back in 1915, California’s kelp forests could be non-existent today.

When it comes to survival, sea otters seem to face extinction time and again, but they also seem to be experts at evading it. However, without the sworn secrecy of a group of 20th-century biologists, the California sea otter could have been wiped out completely before generations alive today had a chance to appreciate the world’s smallest marine mammal.