Southern (California) Sea Otter Population Status and Trends at San Nicolas Island, 2023-Winter 2026

The southern sea otter is a small, playful mammal that lives only along the coast of California. Once hunted nearly to extinction for its fur, the species was listed as threatened, prompting scientists to try a bold experiment: moving a group of otters to a remote island far from the mainland. This island, San Nicolas, was chosen to serve as a safety net, a place where the animals could live away from the dangers of oil spills or human activity that might wipe out the entire mainland population. For decades, researchers have watched to see if these transplanted otters could survive, grow, and eventually thrive on their own. The story of this population is not just about counting animals; it is about understanding how a species interacts with its food, its home, and the changing environment around it. When otters are healthy and well-fed, they eat a lot of shellfish and sea urchins, which in turn helps keep the underwater forests of kelp in balance. But if the population grows too fast or if the food runs out, the otters may struggle, or they might simply leave to find better conditions elsewhere.

For the last several years, a team of scientists from the U.S. Geological Survey, working alongside the U.S. Navy and other agencies, has been carefully tracking this island population. Their latest report covers the years from 2023 through the winter of 2026. The researchers spent their time on boats and on the island's shores, using powerful telescopes to count every otter they could see and to watch how they ate. They wanted to know if the population was growing, shrinking, or staying the same, and whether the otters were using the whole island or just sticking to certain spots. They also watched what the otters were eating, diving deep to see if they were catching their usual meals of sea urchins and snails, or if they were struggling to find food.

The results tell a story of change and movement. As of February 2026, the researchers counted 106 otters on the island. This number represents a decline. Over the three-year period leading up to that count, the population was shrinking by about 8 percent each year. This is the first time since the early days of the experiment that the population has shown such a clear, steady drop. The most significant event driving this change happened in the fall of 2023. For a few years, a large group of more than 40 otters had been living together in a tight cluster off the east end of the island. This group suddenly vanished. The scientists did not see them move to another part of the island; instead, the total number of otters on the entire island dropped at the same time the group disappeared. The researchers believe these otters likely left the island entirely, perhaps swimming back toward the mainland or moving to other islands. One male otter was even spotted nearly a year later off the coast of San Diego, far south of where otters usually live, which supports the idea that they were traveling.

The way the otters use the island has also shifted back to an older pattern. In the past, the otters mostly stayed on the west side of the island, where the water is calmer and kelp forests are thick. For a few years in the middle of the study, they spread out more, with large groups using the north and east sides. But as the large group on the east side disappeared, the remaining otters returned to their historical home on the west end. They are now concentrated in the same areas they used to occupy, particularly in a spot known as "The Boilers," where they gather in the summer and fall when the kelp is at its fullest. In the winter, when the kelp is often gone due to storms, the otters move to the south side of the island, following the food and shelter that the changing seasons provide.

While the population numbers dropped, the researchers also looked closely at what the otters were eating. They observed hundreds of dives, watching the otters crack open shells and eat their meals. The most common food was still the sea urchin, but the otters were eating fewer of the large, red sea urchins and more of the smaller purple ones. They were also eating more snails, clams, and crabs than they had in previous years. This change in diet suggests that the otters are adapting to what is available. The scientists calculated how much energy the otters were getting from their food. The rate at which they gained energy has been slowly decreasing over the last decade, which can happen when a population grows and the best food becomes harder to find. However, the data is not yet precise enough to say for sure if this decline is a sign of a serious problem or just a normal fluctuation. The researchers noted that their ability to watch the otters eat was limited by weather and the fact that they could only observe during the day, so the full picture of what the otters are eating, especially at night, remains incomplete.

The disappearance of the large group of otters highlights a major gap in what scientists know about these animals. They do not yet have a clear way to track where the otters go when they leave the island. The current methods involve counting them visually, which works well when they are there, but cannot follow them once they swim away. The scientists hope to use new technology in the future to tag the otters and track their movements across the ocean, which would help them understand if the population is stable or if animals are constantly coming and going. For now, the report confirms that the southern sea otter population on San Nicolas Island is dynamic and responsive to its environment. The recent decline suggests that the group may have reached a point where it is no longer growing, or that a specific group of otters decided to move on. The researchers will continue to watch, counting the otters and studying their habits, to see if the population will stabilize at this lower number or if it will begin to grow again.