Defenders Magazine

Sea Otters Take a Nose Dive

Are orcas to blame for a recent 70 percent drop along Alaska’s remote Aleutian Island chain?

by Joel Bennett

From the moment naturalist Georg Wilhelm Steller spotted a sea otter near the Aleutian Islands from the Russian ship St. Peter in 1741, humans have for one reason or another been in pursuit of this unique species. Steller referred to it as a “sea-ape” because of its peculiar antics, and other Russians called the otters “little bears.”

Curiosity soon gave way to a ruthless hunt. From numbers too high to count, sea otter populations along this windswept chain of misty islands whipsawed over the next two centuries to almost nothing and then back again.

Over the past decade sea otters have suddenly plummeted again, and scientists are struggling to determine why. Can the Aleutian sea otter once again rebound? And what does the present biological crisis tell us about the health of this critical Bering Sea ecosystem, home to an abundance of species?

The magnitude of the earliest sea otter decline was staggering — it is estimated that between 500,000 and one million otters were killed over 170 years in Alaska . When they became scarce, a single otter pelt fetched $1,000 on the international fur market — a value 10 times greater than any other fur. It was not until 1911 that the International Fur Seal Treaty put an end to otter hunting and a period of new consciousness about otter conservation began.

Sea otters are one of the largest members of the weasel family, often even heavier than the giant otter of South America . A large male can weigh almost 100 pounds. In spite of their weight, they are virtual acrobats underwater and can stay under the surface for several minutes at a time. Otters usually produce one pup, which the mother then clutches to her belly while she swims through rolling ocean swells.

Sea otters are voracious eaters. To maintain their 100-degree body temperature and high metabolic rate, they eat between 20 and 30 percent of their body weight a day — primarily slow-moving invertebrates such as abalone, clams, crabs, mussels and sea urchins. Because they lack the layer of fat common in most marine mammals, they must rely on their dense fur for insulation, which means nearly constant grooming to keep clean.

A 2000 survey by U. S. Fish and Wildlife Service (FWS) biologists made the startling disclosure that the otter population in the central and western Aleutians had dropped by more than 70 percent since 1992, and as much as 90 percent around certain islands. Around the island of Adak , which has the largest human population, FWS biologists counted 470 otters in 2000 — less than half the number seen in 1992. In a free-fall that can only be characterized as catastrophic, there are now thought to be a mere 6,000 sea otters left in the Aleutians , down from 55,000 to 100,000 in the 1980s.

This time authorities knew that the decline was not due to commercial hunting — a thing of the past — or native subsistence hunting, so research was directed at other possible sources of mortality. After discounting disease, starvation, emigration, hunting and reproductive failure, marine biologists Jim Estes and Tim Tinker of the U.S. Geological Survey Biological Resources Division advanced a totally unexpected theory: Tens of thousands of sea otters must have been eaten by orcas, also known as killer whales.

“The number of sea otters went down so fast that it was over before you could blink an eye,” says Estes, who has worked in the Aleutians for years. He and others realized that at about the same time sea otters had plummeted, seals and sea lions became less abundant as well. Killer whales, which up to this point had preyed primarily on seals and sea lions, became the prime suspects. “Although we were skeptical at first, when we did the bookkeeping it all made sense,” says Estes. What researchers didn’t know, however, was whether it was just a few killer whales eating a lot of otters — or a lot of whales eating just a few otters each. By Estes’ calculation, a single killer whale could eat at least 1,800 sea otters in a year — meaning that as few as a half dozen whales could consume tens of thousands of sea otters over several years.

One area in the central Aleutians gave Estes’ theory more credence. On Adak Island, at a place called Clam Lagoon, biologists observed that an otter population of 100 to 200 individuals remained remarkably constant over many years, compared to Kuluk Bay nearby, where the population had declined by more than 70 percent. Estes found that killer whales frequented Kuluk but were barred from Clam Lagoon by a narrow, shallow entrance channel.

“If you’re an otter, it’s a nice place to be,” says Jeff Williams, an FWS biologist in Adak. To stress his point, he tells of how his office clerk witnessed a killer whale seize an otter in Kuluk Bay just outside his office.

As Estes expected, the responses to his killer whale hypothesis have ranged from total acceptance to disbelief. Commercial fishermen tend to be solidly in his camp. While few have actually observed a killer whale attack a sea otter, many believe they would based on the increasing loss of hooked fish to the hungry whales. According to the fishermen, the whales have learned to key in on the sound of the hydraulic longline fishing gear being pulled in from boats. Once they arrive, they feast on the hooked halibut and black cod until nothing is left.

Robert Fowler has fished out of Dutch Harbor for 11 years and has no doubt that killer whales are responsible for the loss of sea otters. “The killer whale is the big bully on the block out here — and he pretty much takes what he wants. First a couple show up off the bow, then more, and they bring the little babies to watch. They can just pluck a fish off the line, leaving a pair of lips hanging on the hook.”

No one has precise information about how much commercial catch is lost to killer whales in the Bering Sea, but authorities with the National Marine Mammal Laboratory say depredation occurs on at least 20 percent of all fishing sets — the placing of longline gear under water — and is believed to be huge. Whether this means the whales are hungrier from lack of their usual food or are merely being conditioned to follow boats because of the large amount of by-catch being thrown overboard is unknown.

Others are not so sure that the blame for otter decline should be put on killer whales. Craig Matkin, an experienced whale researcher in Alaska, believes that there is some evidence that killer whales could hold a population down at low levels once it gets there, but he doubts they were the original cause of the decline of either sea otters or sea lions. He points to the fact that little is known about the movement patterns or the numbers of killer whales in the Bering Sea or how many comprise the transient, marine mammal-eating whales, as opposed to the fish-eating “resident” whales. “We’ve seen no substantial predation by killer whales in the Prince William Sound-Kenai Fiords part of coastal Alaska,” he says. “We shouldn’t jump to conclusions before more data is gathered.”

One of the possible factors that could account for the loss of marine mammals is contaminants. In its 1994 conservation plan for sea otters, FWS stated that preliminary data from the Aleutians suggested that DDT/DDE ratios in sea otters were unexpectedly high. These pesticides become more concentrated as they move up the food chain — a process known as bioaccumulation. FWS is presently cooperating with the Alaska Sea Otter and Sea Lion Commission to retrieve and test otter carcasses for various toxins. Unfortunately, the database for this line of inquiry is small, since few dead otters have been located so far.

Matkin is uncomfortable ruling out contaminants just because few otters have been found — a fact that has been used to bolster the theory that killer whales have eaten them. In fact, he says, otter carcasses could quickly vanish after being beaten against rocky beaches in frequent storms or fed on by scavengers, and not many people during much of the year are out looking for them anyway. Matkin also knows that other Alaska marine mammals high on the food chain have had elevated levels of toxins for years, so why would sea otters be exempt? Most notably, several killer whales from Alaska sampled in 1999 were the most contaminated marine mammals ever measured — primarily from DDTs and PCBs. Such substances travel northward towards Alaska on ocean currents and storm systems from China and Southeast Asia. Nick Prince, a Yupik native from Bristol Bay who now lives and fishes in Adak, advises researchers to “follow the Japanese current. These contaminants are coming from Asia to Adak, and showing up in halibut livers.”

Regardless of how Aleutian sea otters have died, their disappearance has caused an ecological chain reaction, with enormous implications for the health of the near-shore environment of the Bering Sea. This in turn could have serious consequences for the commercial fisheries of the area — the mainstay of the local economy. The primary problem relates to kelp, a marine algae, which is normally maintained in healthy quantities because sea otters prey on the sea urchins that graze on it. Without sea otters, urchins overgraze the kelp, eating the base of the plant so that it becomes detached from the sea floor and dies. Vast patches or “forests” of kelp have now disappeared, removing essential habitat that acts as a foundation of the coastal ecosystem. Fish such as herring, rockfish and juvenile salmon lose important nursery grounds and escape areas. Invertebrates such as crabs, starfish and sea cucumbers lose essential habitat. Even seabirds that dive into the jungle of wavy fronds must now look for food elsewhere. In addition, kelp serves as coastal buffering against severe winter storms.

Whatever factors have produced this crisis for sea otters, most scientists agree that a broad view of the Bering Sea ecosystem must now be taken. And there will be no quick fix. Estes believes that the problem in the Aleutians could be the result of a complex domino effect. “Ultimately, he says, “we have to look at the oceans to see what we’ve done. If it’s killer whales, find out what drove them to prey on sea otters.”

Another human-induced factor, global warming, causes rising temperatures in the Bering Sea that could be affecting fish stocks. Add to this the huge commercial bottomfish fishery, which removes more than a million tons of marine life a year, and the cumulative adverse impact of trawling on the ocean floor over the years, and the task of unraveling the related events and their cumulative impact will be daunting.

If killer whales continue to be implicated as the main factor in the decline of sea otters, there are few direct management options available. Orcas are currently managed by the National Marine Fisheries Service and are protected under the Marine Mammal Protection Act (MMPA). Universally admired for their beauty, strength and intelligence, it would be almost impossible, as a political matter, for any governmental program to control whales by killing them. Some form of non-injurious deterrence has been suggested by beleaguered fishermen, but this would be experimental at best.

Perhaps the best short-term solution is to work on restoring depleted populations of sea lions and seals in the Bering Sea to achieve a better balance of marine mammals. This would in turn reestablish a normal prey base for killer whales. In 1997, the western stock of Steller sea lions — found in Prince William Sound, Alaska and westward — were listed as a federally endangered species, triggering a more aggressive recovery program. Stricter fishing quotas, more extensive “no trawl zones” around sea lion rookeries, the reduction of high amounts of by-catch and the establishment of more marine protected areas are all measures that can aid in the restoration of the seal and sea lion populations.

There is also growing pressure to create a larger, more up-to-date database on contaminants. If insufficient incentives exist to motivate local people to bring in otter carcasses for testing, additional resources could be redirected for this effort. Currently, the state of Alaska is pushing the U.S. Department of Energy to conduct new tests for radioactivity in the sea surrounding Amchitka Island, where the U.S. military detonated three atomic bombs between 1965 and 1971. In its request, the state cites concerns that radioactivity could harm subsistence food users and major commercial fisheries, stressing that no sampling has been done there since the 1970s.

Conservationists believe that a formal listing of the Aleutian sea otter as depleted under the MMPA or endangered under the federal Endangered Species Act is warranted. This would be an important first step in gaining more crucial information and in adequately funding a full-fledged recovery program.

But that may not be enough. For Steller’s “sea-ape,” the future is far from certain. The colossal decline of this keystone species in the Aleutians may well point to the most serious systemic failure of the Bering Sea ecosystem in history. The cooperative efforts of multiple agencies and individuals working together is the best chance of finding the real missing pieces to the elusive puzzle of why the otters have gone.

Joel Bennett, a documentary filmmaker and photographer, is a Defenders field representative in Alaska.