We Alaskans 7/11/99
Copyright Anchorage Daily News

The Otter Enigma

Sea otter populations explode in Southeast and crash in the Aleutians, triggering chain reactions that will alter the ecosystem and the economy.

By Doug Schneider

Thirty. Sixty. One Hundred Feet. Sea Otter No. 23 Quickly Disappeared

into the blue-green depths of Cross Sound, a remote waterway along Southeast Alaska's Icy Strait.

At the surface, Brendan Kelly watched his laptop computer to see how deep the otter was diving. A transmitter attached to the 97-pound male's flipper relayed the depth.

At 300 feet, the otter finally leveled off. ''He's hit bottom,'' said Kelly, a marine mammal scientist at the University of Alaska Fairbanks.

No. 23 was probably looking for lunch, a task that is becoming increasingly competitive as sea otters repopulate areas of Southeast for the first time since Russian and American fur traders hunted them to extinction 150 years ago.

These days, an estimated 10,000 to 15,000 sea otters populate Southeast waters, about as many as probably existed when Vitus Bering stumbled onto the region's rocky coast in 1741 and claimed it for Russia.

The resurgence of sea otters in Southeast is a mixed blessing for the region's residents. Fishermen worry sea otters, which are voracious shellfish predators, will eat too many Dungeness crabs -- a favorite prey and the mainstay of the region's multimillion-dollar commercial fishery. Natives who depend on clam beds for subsistence also worry about the sea otter's impact.

Yet tourists love them, and in a region increasingly dependent on tourism, more sea otters is good news.

''After whales, I'd say the sea otter is the one animal that most impresses visitors,'' said Jim Hammond, operations manager for Auk-Nu Tours, a sightseeing company based in Juneau. ''We have nice viewing out in Icy Strait, where they hang out in the kelp forests. They are an important part of our business.''

But while Southeast is swimming in sea otters, populations in the Aleutian Islands have plummeted nearly 80 percent in the last seven years. Scientists say the two circumstances are not related. In Southeast, abundant prey has fueled the sea otters' dramatic population increase, while predation is responsible for the decline in the Aleutians.

More interesting, say scientists, is what will happen to these two ecosystems as the sea otter populations change.

''Sea otters are a keystone species,'' said Jim Bodkin, a sea otter researcher with the U.S. Geological Survey. ''By definition, that means their presence or absence will trigger a host of significant changes to the ecosystem.''

In Southeast, scientists want to know if too many sea otters will wipe out commercial crab stocks and decimate shellfish beds. In the Aleutians, they wonder if too few will erode the very foundation of the region' s coastal marine food chain.

Largest of the Weasels

The sea otter is the largest of the mustelid family, which includes the mink, river otter, weasel and wolverine. But it's also the smallest marine mammal; adults weigh 60-100 pounds.

They've inhabited the North Pacific since the late Pleistocene era about 20,000 years ago, and Native peoples have harvested them almost that long, using their dense fur and thick hides for clothing and handicrafts. The sea otter still holds an important place in the cultures of Southeast Natives and the Aleuts of the Aleutians

Long and sleek, with large, leathery flippers, sea otters are most comfortable in the water. But they generally stick close to shore and rarely venture more than a few miles from land. That may help explain why Alaska's sea otters went undiscovered by Europeans for so long.

But once discovered, news of abundant sea otters and fur seals led to their exploitation. Russian traders arrived in the mid-1700s, followed by Americans beginning in the late 1700s. Russians aren't entirely to blame for the otters' demise, according to Bob DeArmond, longtime Southeast resident and historian who has written on Alaska's history and who now lives in the Anchorage Pioneers' Home.

''Natives did the hunting and the killing,'' DeArmond said. ''They mostly sold their pelts to the Americans. There were probably 50 American trading vessels here from 1790 to around 1840. By that time there weren't enough sea otters left for it to be worthwhile.''

Seventy-one years later, in 1911, Congress adopted the fur seal treaty, ending legal hunting of sea otters. By then they were considered extinct in Southeast and rare throughout the rest of the state.

Skyrocketing in Southeast

Today it's hard to imagine sea otters were ever missing from Southeast. They can be found in nearly every harbor, floating on their backs while grooming their fur or tending to pups.

From the mid-1800s to the 1960s, there were no sea otters in Southeast. In the late 1960s, federal biologists relocated 412 to Southeast waters from healthy colonies in Prince William Sound and the Aleutians; nearly half went to Khaz Bay. At first, the otter population grew slowly. Then, beginning in the late 1980s, the numbers skyrocketed.

''They're now increasing at a rate of about 20 percent a year in Southeast,'' said Tom Shirley, a marine ecologist at the University of Alaska Fairbanks. ''That's a better return than much of the stock market.''

Today, about 10,000 sea otters live in Southeast. Without accounting for natural mortality and hunting (which is restricted to Alaska Natives), Shirley said that number is expected to double about every five years.

Ironically, Southeast sea otters owe their recovery to their nearly 150-year absence from the region. During that time, Dungeness crabs, urchins, clams, and abalone stocks grew -- becoming easy prey for today's otters.

''The predator niche filled by the sea otter was left empty for a long time after the sea otter was exterminated,'' Kelly said. ''So the prey base was able to expand.''

Crashing in the Aleutians

While life is good for Southeast sea otters, the good times have vanished for their Aleutian brethren. Along this remote 3,500-mile archipelago, sea otter numbers had recovered from the hunting of a century before. Yet in just the last few years, some 45,000 animals -- about 80 percent of the region's population -- have disappeared.

Jim Estes, a marine biologist with the U.S. Geological Survey in Santa Cruz, Calif., has visited the now-abandoned Navy station on Adak Island the last eight summers, studying sea otters. During that time, he's watched the population around the island tumble from 2,500 animals to about 300.

In addition, aerial surveys done in 1965 and again in 1992 show that sea otter numbers were lower at 26 of the 27 major islands in the Aleutian chain.

''That was a pretty clear signature in my mind that something fundamental was going on here -- and on a wide scale,'' Estes said.

Estes and his colleagues conducted studies on the likely culprits -- disease, starvation, pollution and other causes. They ruled out each one.

Another possibility was that something was eating the otters. But what could eat so many over such a large area in so little time? In an article published last October in the journal Science, Estes and his co-authors put forth an unexpected answer: killer whales.

''Even we thought that killer whales being responsible was the most outlandish thing,'' Estes said. ''They don't normally feed on sea otters much, since otters don't offer much in the way of nutritional reward. They are bony, furry creatures without much meat or fat.''

But then he and his colleagues began witnessing killer whale attacks on sea otters in 1991. They found further evidence when they compared two sites: Clam Lagoon, a place where sea otters gather that is too shallow for killer whales, and Karluk Bay, an area frequented by both killer whales and sea otters that's just a few miles away.

Between 1993 and 1997, the Clam Lagoon otter population remained stable while the population on the exposed coast of Karluk Bay declined 76 percent.

Based on killer whale attacks observed at Karluk Bay, Estes estimated that whales could be responsible for the loss of 45,000 sea otters in an area from Kiska Island to Seguam Island, a span of about 300 miles

''That really perked us up,'' Estes said.

Diet studies showed that sea otters could sustain a killer whale, but it takes a lot of sea otters to replace their normal diet of sea lions and seals.

''We calculated that a single killer whale could consume around 1,800 sea otters in one year,'' Estes said. ''So with that figure, four killer whales could be responsible over several years. That's assuming they were eating nothing but sea otters.''

Estes said the killer whale theory is the only one put forth so far that can explain the disappearance of so many otters. But he says it's unlikely that as few as four whales are to blame. He believes more killer whales are eating sea otters. He's not sure exactly how many, but a science cruise in the Pribilof Islands north of the Aleutians last summer counted more than 400 killer whales.

Why killer whales would target sea otters in the Aleutians is a mystery, too. Estes and others suggest that the short supply of such traditional prey as Steller sea lions and seals is a factor.

''Learning more about why this is happening is the next step,'' Estes said.

Otter declines change kelp forest

In the Aleutians, rapidly disappearing sea otters have triggered a host of changes to the marine environment -- all of them linked to each other and, ultimately, to a crucial habitat called the kelp forest.

Kelp forests are large jumbles of seaweed, kelp and algae. Some species, like laminaria, anchor themselves to the seafloor. Others float with the currents. Either way, kelp forests harbor an oasis of sea life.

''Kelp forests are the foundation of the coastal ecosystem,'' Estes said.

Crabs, starfishes, sea cucumbers and urchins live at the base of the forest canopy. Farther up, numerous fish and shellfish find refuge in the kelps' endless green-and-brown tangles as well as easy prey. Species such as herring spawn by laying their eggs on kelp.

The benefits of kelp forests even extend to airborne creatures. Sea birds can find easy prey there.

Kelp forests have just one mortal enemy: sea urchins. These spiny, round animals don't just eat kelp, they chow down on it.

Because otters love to eat urchins, they help kelp forests flourish. But without otters, urchins can quickly decimate a kelp forest.

''When otters aren't present . . . sea urchins come in and go hog wild eating the kelp,'' said Brenda Konar, a kelp forest ecologist at the University of Alaska Fairbanks. ''When urchins clean out a kelp forest we call it 'barren ground' because there's literally nothing left.''

Unfortunately, that may be happening in the Aleutians. With so many sea otters gone, kelp is taking a beating, scientists say.

''As we went through the forests a couple of years ago, we saw thousands of urchins eating the kelp,'' Konar said. ''There was literally nothing left but stumps. It was interesting to witness because you saw the marine community structure changing right there in front of you.''

Without kelp, a variety of species could be in for a tough time, Estes said.

''As an example, halibut, which aren't a kelp bed species per se, do come in and feed in shallow water and consume . . . species that feed on the kelp,'' Estes said. There could be impacts on the region's commercial fisheries if too much kelp is lost.''

Southeast shellfish stocks suffer

While Aleutian otters continue to decline, Southeast Alaska's booming population has hit shellfish stocks hard. Some scientists believe the government's reintroduction of sea otters may have worked too well.

''Typically, sea otters come into a new area and exploit the best prey first,'' said Stephanie Haverlack, a graduate student studying sea otter feeding habits in Southeast. ''They'll start off with clams and crabs and urchins and abalone. They work those populations down to very low levels before going after less-desirable prey like cockles, chitons and marine worms.''

Many of Southeast's best clam beds and crab-fishing areas have been decimated by sea otters. Commercial catches of Dungeness crab are down, and area Natives who once harvested from traditional clam beds now find the beds empty.

''After the otters moved in here in the late '70s, they totally wiped out our subsistence crabs and clams,'' said Mark King, a Chugach native from Cordova and member of the Alaska Sea Otter Commission. ''There are some real small cockles, but no large ones like we used to harvest. They're down to starfish and blue mussels and worms.''

Other species have been hit hard too, said UAF's Shirley.

''Abalone stocks along islands exposed to the open ocean where sea otters were first introduced will probably never come back now, because of the sea otters,'' Shirley said. ''There used to be a small but vigorous fishery there. People blamed the decline on the fishermen, but in fact it may have been the continuing increase in otter populations.''

The damage sea otters wreak on shellfish is due to their need to keep warm against the cold North Pacific. Although otters have the densest fur of any mammal, they lack the insulating layer of blubber that protects seals and other marine mammals. So otters must burn a lot of energy to stay warm.

To get it, otters eat up to 30 percent of their body weight each day to stay warm, Estes said. That translates into a lot of crab.

''One study done in Prince William Sound found that a sea otter could eat 14 adult Dungeness crabs per day, if that's the only thing it ate,'' Shirley said. ''If you take 10,000 and multiply it by 14, you can see that the current population of sea otters could eat the entire commercial Dungeness catch in Southeast Alaska in less than two weeks.''

To be sure, sea otters alone are not responsible for the region's declining crab stocks. Other factors include fishing, natural crab population cycles, ocean temperature and other predators. But as otters continue to increase, Southeast's ecosystem appears headed toward a time reminiscent of the days just before the Russians arrived.

''I think commercial fishermen have seen the handwriting on the wall,'' Shirley said. ''The otters are coming back, and we're basically getting our crab numbers back to a natural level.''

Next stop, Glacier Bay

Just a few years ago, Glacier Bay National Park had no sea otters. Today close to 500 reside there.

At the same time, Dungeness crab stocks in the bay have declined 35 percent during the past seven years, said Shirley, who studies the bay's crab stocks.

''All of the bays show the same downward decline,'' Shirley said. ''Whether or not that is due to sea otters or to a long-term cycle, we don't know.''

For years, the National Park Service has tried to ban commercial crab fishing in waters it claims. Crab biologist Jim Taggart of the U.S. Geological Survey said the growing otter population may soon make the bay unprofitable for commercial fishermen.

''That's an interesting detail in all of the negotiations . . . over the plan to close the park to commercial fishing,'' Taggart said. ''A significant amount of money may be allocated to buy out Dungeness crab fishermen so that the park can be closed to fishing. And yet, in a relatively short period of time, there is probably not going to be any fishery . . . because of otter predation.''

Running for cover

But Dungeness crabs may have found an escape, according to Karen Scheding. She's finishing her master's degree study on the distribution of crabs in Southeast -- in bays with sea otters and those without them. One of the bays, Dundas Bay in Icy Strait, has had a growing sea otter population since 1989.

''There is something interesting happening there,'' Scheding said.

Scheding said the bay used to have large numbers of Dungeness crab in the shallow areas. Shortly after sea otters moved in, Scheding started catching fewer Dungeness crabs in her traps. Fishermen have encountered similar shortages, she said.

''There are still Dungeness there but now they are found primarily at depths sea otters can't reach,'' Scheding said. ''We found lots of them at depths close to 600 feet, far out of reach of sea otters and probably too deep for fishermen to bother with,'' Scheding said. ''The population may be reacting in that it doesn't come up into the shallows much anymore.''

Scheding can't say for sure whether these deep-dwelling crabs are escaping sea otters, are there because of a migration pattern or have always been there. Still, when she looked for Dungeness crabs in areas lacking sea otters, she found them in shallow water but not in deep water.

Bubbling Up

Back in Icy Strait, researchers Bodkin and Kelly bobbed atop a gentle ocean swell in their 25-foot Boston Whaler, watching their computer's readout of sea otter No. 23's dive.

''They are fairly rapid swimmers,'' Bodkin said. ''It takes them only about 90 seconds to get down to 300 feet. With a maximum dive time of four to five minutes, that doesn't leave them with much time on the bottom.''

Having tracked more than 4,000 otter dives in Southeast, Bodkin and Kelly have found that otters routinely dive deeper than previously thought. ''They are effectively foraging twice as deep as we thought,'' Kelly said.

After a few minutes, the number on the computer screen began changing again.

''He's on his way up,'' Kelly said. ''Twenty meters. Ten . . . five, four, three . . .''

Bodkin watched through a high-powered spotting scope as the otter broke the surface about a quarter-mile away. It rolled onto its back, then quickly pried open the shell of a large clam and slurped its meaty contents, oblivious to its role in the ecosystem.

Doug Schneider is the science writer at the Alaska Sea Grant Program at the University of Alaska Fairbanks.