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Over a decades-long career as a federal scientist, Jim Estes’s groundbreaking work on sea otters has shown just how much these fuzzy animals can teach us about how the world’s ecosystems work.

A Series of Fortunate Events

Jim Estes smiles at the camera
Former USGS scientist Jim Estes

While some scientists are drawn to their study systems from childhood, biologist Jim Estes came to studying otters in the way that so many others come to their life’s work—through a series of fortunate but largely unplanned events.

Born in Sacramento, Estes went off to college at the University of Minnesota without any intention of studying biology. He went to college on a baseball scholarship, and baseball was his main area of interest at the time. But he took an introductory biology course his first year, and it resonated with him, so he declared biology as a major.

After college, Estes decided to continue with biology, completing a master’s degree about African elephants at Washington State University in 1969. At that time, the country was in the middle of the Vietnam War. Estes was prepared to join the military, but to his surprise, he flunked the physical exam. He happened to mention a minor instability in his knee to the examiner—an old baseball injury—"and his eyes got big and he just said, you're out of here man,” recalled Estes.

The knee never bothered him for the rest of his life, but flunking that physical exam was a major turning point in Estes’s life. He had to figure out what to do next. And what came next was sea otters.

All the World is Green

While Estes was trying to figure out his next step after being rejected from the military, a professor friend, Vince Schultz, contacted him with a lead: the Atomic Energy Commission was looking for someone to study sea otters in the Aleutian Islands, a string of islands stretching from southern Alaska to nearly Russia. The Cannikin Nuclear Test was to take place in 1971 on the uninhabited Amchitka Island, and in response to controversy surrounding the test, the Commission requested a study of the impacts of the test on sea otters.  Schultz recommended Estes. Though Estes had not worked with sea otters, Schultz thought he’d be good at it. And off he went to Alaska.

Estes used what he learned about sea otters during his Atomic Energy Commission study to complete his PhD dissertation in 1974 at Arizona State University. He was hired that same year by the U.S. Fish and Wildlife Service, beginning his decades long career with the Department of Interior (DOI), and sea otters remained his primary focus through most of those years. Working in federal science made it possible to maintain a long-term research program that provided a deep understanding of just how important sea otters are to marine ecosystems.

A young Jim Estes sits near the campfire with snowy mountains in the back, circa 1972
Jim Estes on Attu Island in 1972

As Estes began his work on sea otters, the field of ecology was just beginning to think about the role of predators like sea otters in a new way. An influential 1960 paper outlined what came to be known as the “green world hypothesis,” which argued that the world was covered in green vegetation because predators limited herbivore populations. A few years later, an ecologist and University of Washington professor Robert (Bob) Paine published the results of an experiment where sea stars were removed from rocky tide pools where they were a top predator, which dramatically reduced the diversity of the ecosystem. Paine then coined the term ‘keystone predator.’ These publications and others suggested that predators had a major role to play in shaping ecosystems, but this idea was still new when Estes was starting out as a budding PhD scientist.

Early on, Estes thought he’d study the effects of the environment on sea otters. But a chance conversation flipped that idea on its head and set the course of Estes’s career. Paine, who conducted the sea star experiment, happened to visit Amchitka Island where Estes was working, and they chatted about Estes’s research plans. Paine thought the idea of studying the effect of the environment on sea otters was uninteresting. Had he considered studying how sea otters affected the ecosystem instead?

That question really resonated with Estes. The Aleutians were a place where sea otters were still recovering after being hunted to near extinction during the Maritime fur trade in the mid-late 1800s. The otters had been protected in the early 1900s, and by the 1970s, otter populations had recovered in some places, but remained absent from others.

“I said, here's a fabulous natural experiment that we can use to maybe answer that question,” recalled Estes, “So I went off to Attu Island, which didn't have any otters, and that was sort of the beginning of it all.”

When Estes scuba-dived at an island with lots of sea otters, there was lots of kelp. But he didn’t connect the otters with the kelp until he went diving at Attu, an island without otters. There, he found urchins covering the sea floor and little kelp.

“It became clear in an instant,” says Estes. Based on his surveys at the islands with and without otters, Estes proposed in a 1974 paper that sea otters were the primary cause of the differences in the marine communities. When sea otters were present, they ate urchins, which feed on kelp, allowing the kelp forest to thrive. When otters were absent, the urchin populations grew and devastated kelp forests. The sea otter, wrote Estes and co-author John Palmisano, is “an evolutionary component essential to the integrity and stability of the ecosystem.”

Otters All the Way Down

Two sea otters floating on their backs in water.
Two sea otters float in the ocean.

From there, the sea otter-urchin-kelp system became a classic example of a top-down, predator controlled trophic cascade, the type of strong but indirect interaction described in the Green World Hypothesis. And the natural experiment of the Aleutian Islands was the perfect place to learn just how far the reach of sea otters extended. Study after study, Estes found that the impacts of otters on the ecosystem were widespread, powerful, and consistent.

Sea otters influenced the diets of gulls and bald eagles, the size of local fish populations, the biomass and size of sea stars, and the growth rates of mussels and barnacles.

“I was once accused at one point in my life by somebody, sort of tongue in cheek, the next thing you're going to tell us is that otters caused the ice ages,” Estes recounts.

That was a joke, Estes says, otters didn’t cause the ice ages, but it’s not so far from the truth, either. Since sea otters eat sea urchins and allow carbon-sequestering kelp to flourish, otters do have a local impact on carbon dynamics and indirectly influence the climate.

And while sea otters are only found in the coastal North Pacific, mostly along the coasts of California, British Columbia, Alaska, and Russia, ecosystems all over the world have their own equivalents of sea otters, predators that exert powerful top-down effects on the system. When Estes organized a meeting in 2007 to learn just how widespread this type of dynamic was, the participants generated a long list of examples. A sample of that list includes wolves, elk, and willows in Yellowstone; predatory crabs, snails, and saltmarsh cordgrass in the southeastern United States; fish, lobsters, sea urchins, and kelp in New Zealand; and big cats, baboons, and small mammals in Ghana.

How to Solve a Marine Mystery: From History to Technology

The late 1990s brought shifts for Estes’s career. It was during this time that Estes moved from the USFWS to the USGS during a series of organizational changes for biological research in DOI. It was also around this time that Estes was considering moving on from the sea otter system to study something else.

A sea otter resting in kelp as two orcas swim past. Glacier Bay at Point Carolus, Alaska
A sea otter resting in kelp as two orcas swim past. Photo taken in Glacier Bay at Point Carolus, Alaska

As it turned out, Estes stuck with sea otters, because in the Aleutian islands sea otters were experiencing a dramatic shift of their own. Over the first two decades that Estes studied the sea otters there, his research largely told a story of recovery. His ‘otter-no otter’ concept had been founded in the premise that sea otter populations were thriving at many islands. But in the early 90s, Estes and colleague Tim Tinker observed that many of these previously thriving populations had collapsed. Studying sea otters so intensely and for so many years set Estes up not only to notice the change but also to take on the challenge of figuring out what had happened. Ultimately, Estes and colleagues concluded that killer whales were consuming sea otters, and that the killer whale feeding strategy had been influenced by declining ‘great-whale’ populations in the northern Pacific after WWII through 1970 due to an increase in modern commercial whaling.

Estes has observed over the course of his career how different approaches to ecology contribute to answering big questions like these. Solving the sea otter collapse mystery required synthesizing many different types of information and collaborations with physiologists, modelers, and oceanographers. It drew on observations from the field as well as modern statistics and computer power. His work was strongly influenced by experimentalists like Paine, he says, but his sea otter or kelp forest work could have never been discovered through any purposeful experiment.

Answering these questions also required a keen understanding of history—including both long term evolutionary history and modern human history. It would be impossible to understand sea otter dynamics without understanding evolutionary history of the North Pacific and the history of the fur trade and whaling.

“Much of what we have learned and can learn about the way the world works, why species are where they are, and why the distribution and abundance of species is as it is, that history is an absolutely essential dimension to understanding those things,” says Estes.

Estes retired from the federal workforce in 2007, though he continued to collaborate with USGS scientist Tim Tinker in a joint lab at the University of California, Santa Cruz. Following his retirement, he continued to work as a professor at the University of California, Santa Cruz, retiring from that role in 2018.

Close up of resting sea otter in Homer harbor in Alaska. Otter has eyes closed.
A resting sea otter with eyes closed. Photo taken in the Homer harbor in Alaska. Sea otters provide one of the best documented examples of top-down forcing effects on the structure and function of nearshore marine ecosystems in the North Pacific Ocean

After decades of challenging field seasons, hundreds of scientific papers, numerous awards, and election to the National Academy of Sciences, it is clear Estes’s career is the result of a lot of hard work, but he often reflects on the role fortune played in setting the whole thing in motion (he titled a book about his life Serendipity).

“I just feel so lucky that I was there when that opportunity came along and wound up in a place where I got to do these kinds of things,” he says, “It was just fabulous wilderness. And it was such an exciting place to be scientifically, and it was an exciting place to be because these islands were just an amazing laboratory for doing large scale comparative ecology.”


For more information on Dr. James Estes, please contact A. Keith Miles.

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