Sea otters’ stone tools provide new clues for archeologists

Animal archeology could reveal where sea otters lived in past, how tool use evolved

A sea otter cracks open mussels with a rock at Elkhorn Slough, near the study site. (Jessica Fujii/Monterey Bay Aquarium)


Archeologists dig up clues about the lives of ancient humans by studying the tools and piles of trash they left behind. Now, it turns out they can do the same thing with another species of skilled tool users in the midst of their own “Stone Age” — sea otters.

This kind of “animal archeology” could open up a new window into the past and has already generated new discoveries, such as the fact that most otters appear to be right-handed, researchers say.

Sea otters use stones as tools to pound and crack open snails, mussels, clams and other seafood that can be hard to open with their teeth and paws.

It turns out all that pounding can also be damaging to the shell-cracking tools involved — that is, the stones — “creating a distinctive archeological record that parallels and may even pre-date that of the humans they currently live alongside,” reports a new study led by Michael Haslam, an independent archeologist based in London, England.

Within their first hour of being out there, they had already found something that we’d missed for decades.– Tim Tinker, biologist

Canadian biologist Tim Tinker, a co-author of the new paper published today in the journal Scientific Reports, has been studying sea otters on the California coast with his team for decades. He had noticed their pounding leaves the shells unusually damaged.

“They’re the most destructive things in the natural environment other than humans,” said Tinker, an adjunct professor at the University of California, Dalhousie University and the University of Victoria, who is now based in Halifax. “There’s really nothing that can smash a clam or urchin or snail with the same sort of force that a sea otter can.”

Sea otters enjoy mussels crusted to drainage pipes at Bennett Slough Culverts. (Michael Haslam)

Several years ago, Haslam, then a research fellow at Oxford University, invited Tinker to a meeting about the new field of “animal archeology.” Haslam had studied the use of stone tools in monkeys and apes using archeological techniques, and proposed doing similar research on sea otters.

Tinker said he was skeptical, since sea otters mostly use rocks that they collect in the bottom of the ocean. After use, they drop the rocks back into the sea, where they would be very difficult to find again.

But he invited Haslam and Natalie Uomini, an archeologist and anthropologist at Max Planck Institute for the Science of Human History, to California to see the otters.

A sea otter eats a mussel that it opened with a stone that it rests on its belly. (Jessica Fujii/Monterey Bay Aquarium)

After visiting several sites where sea otters were floating on their backs, carrying rocks on their chests and using them to crack food open, Tinker and his team took their visitors to Bennett Slough Culverts in Moss Landing, Calif., where otters pull off and eat mussels encrusted on a series of drainage pipes. The otters can’t collect stones from the bottom there because it’s muddy. But humans had piled rocks along the side of the road that the otters were pounding the mussels on.

Rock study

Tinker, a biologist, said the archeologists “immediately did something we’d never done — climbed down, scrambled over the rocks, right down into the water, basically, and started studying the rocks that the otters were pounding their mussels on.”

Uomini recalls that initially, they didn’t see anything unusual about the rocks. Then they started noticing broken mussel shells piled up in certain places.

“At first we thought, ‘Hey, that’s funny. Somebody must have come here, and had a picnic and eaten loads of mussels,'” said Uomini, who mostly studies stone tools made by ancient human relatives 500,000 to a million years ago..

Then it occurred to her that since the mussels were raw, that “somebody” was probably otters, not humans.

“And then we realized these piles of mussels were everywhere, and that there were damaged rocks near them.”

Natalie Uomini sets up her camera to observe otters at Elkhorn Slough, close to Bennett Slough Landing in Moss Landing, Calif. (Michael Haslam)

Tinker said he was dumbfounded: “Within their first hour of being out there, they had already found something that we’d missed for decades.”

That highlights the power of researchers from very different disciplines working together on problem “and bringing different ways of looking at nature together,” he added.

The team examined the piles of shells, which the archeologists call middens — the same word used to describe the trash heaps left by ancient humans that are also a rich source of archeological information.

They shot video of the otters pounding the mussels against the rocks and mapped the rocks themselves.

They found the otters tend to pound on points and ridges on the side of the rocks facing the water, leaving them smooth, worn down and lighter in colour.

The otters pound mussels on ridges and points on the side of the rocks facing the water, causing characteristic damage. (Michael Haslam)

Caught right-handed

The pounded shells also show an unusual pattern — the right shell is always broken, and the left never is.

Tinker said video observations showed the otters were holding the shells in a very precise way as they pounded.

“Right before they hit the rock, they slightly twist the shell so that their right hand is the one that’s really smashing it on the rock,” he said. The finding suggests that most otters — like most humans — are right handed.

Wild sea otter at Bennett Slough Culverts opening mussels using emergent anvil stone. (Jessica Fujii/Monterey Bay Aquarium)

Jessica Fujii, a senior research biologist with the Monterey Bay Aquarium and co-author of the paper, says the team hopes to see if they can find similar patterns on similar rocks at other locations used by otters. So far, they’re not sure if those patterns apply just to otters eating mussels or if they’re similar for other shellfish.

In any case, Fujii said using archeological methods opens up lots of new research opportunities.

“It’s kind of a whole new field.”

By looking for those sea otter signatures from the past, researchers may be able to uncover new information, such as how widely they were distributed before they were nearly wiped out by the fur trade in the early 20th century. (They are currently still listed as endangered on the IUCN Red List, threatened in the U.S., and a species of special concern in Canada). It may even be possible to get information about how sea otters’ diets have evolved over time or how and when tool use evolved in sea otters, the researchers suggest.

And knowing what rocks — and piles of shells — look like after being pounded by a feasting otter can prevent archeologists from confusing them from those left behind by ancient humans, the researchers note. Previously, Tinker said, biologists had assumed that because sea otters moved so much from place to place, they never left big piles of shells in any one place. But it turns out some underwater otter middens at Bennett Slough Culverts could contain more than 100,000 shells. Similar piles may well have been mistaken for human middens in the past.

Sea otters leave the right side of the mussel shell broken and the left side unbroken. Observations suggest they tend to be right-handed. (Michael Haslam/Neil Smith/Scientific Reports)

Erin Rechsteiner is a research ecologist with the Hakai Institute and a PhD candidate at the University of Victoria who studies sea otters on the B.C. coast. She wasn’t involved in the study, but has worked with some of the co-authors.

She says B.C. sea otters use rocks to pry abalone off boulders or break open shells.

“You rarely see them eating snails without using a rock.”

She has never seen them using fixed boulders like the ones at Bennett Slough Culverts, but wonders if they break mussel shells open the same way with individual rocks.

Rechsteiner said she thinks looking for an archeological record for otters is a “cool idea.”

“I think it could give us a lot of insights into the past.”

The new study was funded by the European Research Council, the Max Planck Institute for the Science of Human History, the Monterey Bay Aquarium, the US Geological Survey and the University of California, Santa Cruz.

This could explain all those strange happenings in Alaska’s waters

Bears feeding on a fin whale carcass in Larson Bay, Alaska. Photo: NOAA© Provided by WP Company LLC d/b/a The Washington Post Bears feeding on a fin whale carcass in Larson Bay, Alaska. Photo: NOAA

The Washington Post
by Ryan Schuessler

New research is shedding light on how far toxic algae blooms have spread in Alaska, and surprised scientists are saying this is just the beginning.

A study from the National Oceanic and Atmospheric Administration’s Northwest fisheries center found domoic acid and saxitoxin – algae-produced neurotoxins that are deadly in high doses — in 13 marine mammal species across Alaska, including as far north as the Beaufort and Chukchi seas.

Researchers say the study is just the latest piece of evidence that warming ocean temperatures are allowing these blooms to stretch into Arctic ecosystems, threatening marine life and the communities who rely on the sea to survive.

“The waters are warming, the sea ice is melting, and we are getting more light in those waters,” said Kathi Lefebvre, NOAA Fisheries research scientist. “Those conditions, without a doubt, are more favorable for algal growth. With that comes harmful algae.”

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The study, which analyzed more than 900 samples taken from stranded or harvested marine mammals in Alaska between 2004 and 2013, found algal toxins in all species sampled, including bowhead whales, fur seals and sea otters.

“We were surprised,” Lefebvre said. “We did not expect these toxins to be present in the food web in high enough levels to be detected in these predators.”

“There seems to be a potential risk for marine mammal health,” she added. “Then there’s also a seafood security risk, in that these communities rely on and depend on these animals for food.”

“I think that’s going to have a huge impact on the Native communities and coastal communities in Alaska,” said Bruce Wright, senior scientist for the Aleutian and Pribilof Island Association, the federally recognized tribal organization of Alaska’s indigenous Aleut citizens. “I think that we’re going to see a number of shifts in our ecosystem as a consequence of warming, and I think some species will be displaced by other species, and others will disappear. There [are] going to be consequences and people are going to have to adapt.”

NOAA’s new study, released last week, comes after months of strange marine life die offs in Alaska. Last year, NOAA declared the deaths of more than 30 whales in the Gulf of Alaska to be an unusual mortality event. Just last month, thousands of dead birds began washing ashore in Prince William Sound.

“I’m pretty sure that’s associated with these algal blooms,” Wright said of the bird die offs and other events. Toxic algal blooms in the region, particularly 2015’s, likely wipe out entire parts of the lower food chain, he added, the effects of which reverberate through the ecosystem.

A massive toxic algal bloom, believed the largest ever recorded, reaped havoc in the Pacific in 2015. Stretching from southern California north to the Aleutian Islands and Bering Sea, it prompted the closure of recreational and commercial fisheries across the American and Canadian coastlines.

“It really does point out that there is a need for more monitoring,” Lefebvre said.

Increasingly warm waters in the north Pacific are believed to be behind other strange disease outbreaks as well. A recent study from the University of Puget Sound found that warmer waters in 2014 contributed to an epidemic of sea star wasting disease in the North Pacific, which decimated starfish populations in the north Pacific.

“My thought is, absolutely, the environment is changing very rapidly in Alaska,” Lefebvre said. “And it’s warming, and there are changes in fundamental parts of the ecosystem.”

She added: “And these ecosystems have developed over millions of years, so when they’re rapidly changing, the chances they’re going to be changed for the better, over all, are very slim.”

Climate Change May Impact Predators to Influence Entire Ecosystems

Predators play crucial roles in ecosystems. They weed out prey that are sick or old, and they can even push species to move in order to stay in their climatic comfort zones. Now, scientists have taken a look at how climate change might impact predators which could, in turn, affect entire ecosystems…

A historical example of this particular phenomenon is the sea otter. These mammals were once decimated by the fur trade that spanned the late 1700s to the early 1900s. This important predator species regulated prey in areas spanning from Alaska to Baja California, Mexico.

“The near extinction of sea otters is one of the most dramatic examples of human-induced impacts to the structure and functioning of temperate nearshore marine ecosystems,” said Rebecca G. Martone, one of the researchers, in a news release.

Without sea otters, which live on abalone, clams, crabs, mussels, shrimp and sea urchins, kelp forests suffer. Without the otters, undersea urchins prey on kelp forests, causing dense areas to become barren and essentially disrupting entire ecosystems. In fact, scientists found that this may even have an effect on climate change.

Kelp forests grow rapidly and store large amounts of carbon. This means that if otters are absent and urchins are destroying these forests, more carbon is released. Not only that, but kelp provides a three-dimensional habitat for species such as rockfish, seals, sea lions, whales, gulls, terns, snowy egrets and some short birds. Without otters, though, these communities rapidly decline.

The analysis of the effect of sea otters shows that predators play huge roles in ecosystems. This means that climate change that affects predators negatively can also greatly impact ecosystems. A symposium focusing on climate’s effects on predators will occur during the Ecological Society of America’s 99th Annual Meeting in Sacramento, California.

Sea otter return boosts ailing seagrass in California

[Proof that nature can take care of her own, if only we’d step aside and let her…]

Sea otter return boosts ailing seagrass in California

By Suzi Gage BBC News

sea otter ecology A sea otter enjoys a crab in California, and helps seagrass in the process.

The return of sea otters to an estuary on the central Californian coast has significantly improved the health of seagrass, new research has found.

Seagrass was deemed to be heading for extinction in this region before the otters returned.

But scientists found that the animals triggered a chain reaction of events that boosted the water-dwelling plants.

The research is published in the journal, PNAS.

The urbanisation of California has led to a huge increase in nutrient pollution in coastal waters, from increasing use of nitrogen-rich fertilizers.

Continue reading the main story

“Start Quote

It’s almost like these sea otters are fighting the effects of poor water quality”

End Quote Brent Hughes University of California

This is said to be the reason for the dieback of seagrass, which has also been declining worldwide.

This research suggests that the hunting to near-extinction of sea otters in the late 19th and early 20th Century may have exacerbated the problem, and conversely that their reintroduction is helping revive ailing seagrass populations, even in the face of hugely nutrient-rich water.

Links in the chain

The researchers assessed seagrass levels over the past 50 years in the Elkhorn Slough in Monterey Bay, and mapped their increases and declines.

They looked at a variety of changes that may have affected the grass, but the only factor that really matched the changes in seagrass was sea otter numbers.

They theorised that sea otters were eating the crabs which prey upon small invertebrates in the water.

These invertebrates eat a type of algae which blooms when there are more nutrients in the soil. It grows on the leaves of the seagrass, shading them from sunlight and causing them to die back.

This is quite a complex cascade of effects, so the researchers tested out their theory by comparing similar estuaries with and without sea otters, and by doing experiments in the lab, and in the field.

These experiments, which included putting cages that sea otters either could or couldn’t access, down on the seagrass, confirmed their hypothesis.

otters Sea otters have been responsible for improving the health of the seagrass in these estuaries.

Brent Hughes, lead author of the study, said: “This estuary is part of one of the most polluted systems in the entire world, but you can still get this healthy thriving habitat, and it’s all because of the sea otters.

“So it’s almost like these sea otters are fighting the effects of poor water quality.”

Hughes described seagrass as “the canary in the coalmine” in terms of predicting levels of nutrient pollution in the water.

Foundation species

It also acts as a nursery habitat for many species of fish and it uses CO2 from sea water and the atmosphere, thus potentially helping with climate change.

Not only that, but it acts as protection to the stability of the shoreline.

Hughes said: “It’s what we call a foundation species, like kelp forest, salt marsh or coral reef. The major problem from a global perspective is that seagrass is declining worldwide. And one of the major drivers of this decline has been nutrient inputs from anthropogenic sources, via agriculture or urban runoff.”

These findings are of particular interest at the moment, as a ban on sea otters moving along the coast to southern California was lifted last year. The ban was in place as there was a fear the sea otters would impinge on fisheries in the area.

Hughes told BBC news: “That’s important because there’s a lot of these kind of degraded estuaries in southern California because of all the urban runoff from places like Los Angeles and San Diego.

“Coastal managers will now have a better sense of what’s going to happen when sea otters move in to their systems.

“There’s a huge potential benefit to sea otters returning to these estuaries, and in to these seagrass beds that might be threatened.”

Otters—a Pinnacle of Evolution

As is often the case, I awoke this morning to the sensation of our cat walking gingerly across my head. Sleek and silky, with luxuriant dark fur, Winnie reminds me of the river otter I saw yesterday afternoon crossing the road and heading upstream into our backyard beaver pond system.

I’d been hoping the otter I have been seeing in the waterways nearby would find our ponds, which are fed by several small streams flowing out of the surrounding hills. Though the ponds turn a light brown this time of year from the clay-rich soil leaching from their banks, they support a healthy variety of life, from frogs, fish and crawdads; to ducks, herons, kingfishers and osprey; to beaver, muskrat, raccoon, mink…and now otter.

A descendant of the diverse weasel family, the river otter is a pinnacle of evolution if ever there were one. While their kin adapted to every other habitat in North America—the ermine and pine marten, to the snowy north woods; fisher, the ancient forests; mink, the riparian zones; badger, the arid plains; and wolverine, the mountainous high country—river otters are masters of inland waterways and freshwater lakes. To those who know them, “otter” is synonymous with the word “play.” Among the most spirited of species, they clearly enjoy themselves in the water, delighting in games with each other like tag and hide-and-go-seek. They also enjoy snow sports: otter “slides” are a familiar sight on snowy slopes along frozen rivers in winter.

Like every other fur-bearer on the continent, otters were nearly decimated during the mindless fur trade era. Unbelievably, otters are still killed in traps set by nineteenth century throw-backs even today. Others are shot by selfish humans unwilling to share aquatic resources that otters had adapted to hundreds of thousands of years before Homo sapiens reached the Western Hemisphere.

The threat of human greed is even more pervasive for sea otters, who have all but lost their ability to move about on land, giving themselves and their terrestrial origins up to their oceanic habitat. Unlike commercial fishermen, they don’t sit out the storms in a cozy home or a dry shack heated by an oil furnace; they spend day and night floating among the coastal kelp beds.

River otter are more than welcome to stay as long as they like here in our beaver ponds. Hopefully we’ll get an occasional glimpse of them swimming fluidly by, or moving on land with their trademark weasel-esque, undulating lope. I’m just glad Winnie is lighter afoot when she tip-toes across my head in the morning.


Back To the Bad Old Days

What’s up with all the anti-wildlife legislation going on around the country these days? Everywhere you look there’s some state senator or representative introducing bills to keep non-human animals down and implement some new form of cruelty to punish them for the crime of not being born of our privileged species.

A few examples: a self-amused eastern Washington representative is calling for east-side wolves to be moved out of his district to the west side of the Cascade Mountains; at the same time Washington State politicians just introduced three bills to make it easier for ranchers to use lethal measures on wolves whenever they see fit; and of course you’ve heard that Montana’s public servants are on a rampage to get rid of their resident wolves. Now one of their legislators wants to lower the minimum hunting age for that state to nine years old.

Meanwhile, in Alaska, a senator just put forth legislation to instate a $100.00 bounty on sea otters! Never mind that these playful, aquatic mammals were nearly completely wiped out during the fur trade era, are critically endangered or extinct from much of their former range and are still listed in Alaska as Threatened or Endangered under the federal ESA, those poor, underpaid (sarcasm intended) commercial crab fishermen see them as competition. (Far from downtrodden, crabbers take pride in being the wealthiest of commercial fishermen; no doubt the senator who proposed the bounty is counting on a kickback into his campaign coffers from the crabbing industry for his otter oppression bill.)

And the list of detrimental anti-wildlife legislation goes on and on.

Is it just me, or have good ol’ boy state politicians stepped up the pace of non-human animal persecution? It’s as though they’re intentionally trying to drag us back to the bad old days of the 1800s, arguably this country’s most reckless period for uncontrolled animal exploitation—besides, perhaps, the present.

Take Action:

Not surprisingly, state legislators only take input from residents of their given state, but since there are bogus bills and measures cropping up across the country, there should be something to speak out against wherever you live. For instance, if you live in Washington State, contact your senator and urge them to oppose anti-wolf bills SB 5187, SB 5188 and SB 5193. Let them know:

  • These three bills would undermine the state’s wolf management plan by giving authority to the county legislators and local sheriffs over the state wildlife agency biologists, and would allow the public to override the state and kill wolves perceived to be a threat to livestock on public and private lands.
  • There are only 50 wolves in Washington.  Now is not the time to remove their protection.
  • Washington’s wolf management plan was created with massive public involvement and adopted unanimously by the Washington Wildlife Commission; powerful ranching advocates should not be allowed to undermine it.
Text and Wildlife Photography ©Jim Robertson, 2013. All Rights Reserved

Text and Wildlife Photography ©Jim Robertson, 2013. All Rights Reserved