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Ancient Aleut stabilized Pacific marine ecosystem, study finds

Doug O'Harra
Smithsonian Institution photo

During the 5,000 years Aleuts lived on Sanak Island off the Alaska Peninsula — perhaps one of the longest occupied locales in the Far North — they scarfed down just about everything that squirmed, wiggled, oozed or splashed through the roiling sea. 

Clams, mussels, algae, kelp, snails, crabs, salmon, cod, seals, sea lions — whatever was easiest to snatch or kill was on the menu. When one species got scarce, they switched as easily as a diner at well-appointed smorgasbord. Unlike other animals that subsisted off the near-shore waters along the rim of the Pacific Ocean, these human omnivores could dramatically alter their diet in response to scarcity. 

This flexibility by a top predator — in this case, those shrewd humans working the tide line or paddling amid the coves in skin kayaks — appears to have stabilized the marine ecosystem for thousands of years, according to a team of scientists involved in the long-term Sanak Island Biocomplexity Project.

“This is our first detailed picture of how humans fit into food webs,” ecologist Jennifer Dunne of the Santa Fe Institute in New Mexico told a special symposium at the 2012 annual meeting of the American Association for the Advancement of Science. Based on archaeological and biological evidence, the scientists discovered that the humans played a special role in the marine food web, acting as “super generalists” that munched on a greater variety of species than most other predators.

They “were very tightly connected to nearly all the species in the marine ecosystem,” Dunne said in a Science Now story provocatively titled — No Omnivore’s Dilemma for Alaskan Hunter-Gatherers. “The Aleuts were positioned to have great effects on local diversity.”

“They … were highly omnivorous,” she added in a SFI story, “eating everything from kelp to sea otters.”

Dunne is part of a remarkable, ongoing multi-disciplinary investigation focusing on the ancient Aleut culture that thrived for millennia along the Alaska Peninsula and in rich island enclaves such as Sanak.

Led by archaeologist Herbert Maschner at Idaho State University, over the past dozen years the team has excavated hundreds of ancient sites in the western Alaska Peninsula region. Included are digs at 33 ancient villages occupied off and on during the past 4,600 years on Sanak Island, located about 30 miles south of False Pass on the brink of North Pacific’s most productive waters.

By one account, Maschner, Dunne and others examined 115,000 bits of remains and 163 pounds of ancient shellfish garbage taken from more than 30 former settlements along Sanak’s craggy shore, according to one recent paper.

With the data, they created a detailed food web that involved 500 different species interconnected via 6,000 links. Among these different critters — from sea stars to sea otters to sea lions — the human Aleuts were among the champion networkers.

“In the intertidal food web, for example, the Aleuts ate the highest number of different prey, 50 of 171 species, with a sea fish and marine crab taking the next slots, consuming 39 and 37 species respectively,” according to the Science Now story about the project.

“In the marine food web, however, the Pacific cod takes the top spot, munching on 124 of the 513 species, although the Aleuts aren’t far behind with a diet encompassing 122 species.”

Even if they weren’t specifically on the menu, most of the animals contributed indirectly to the Aleut diet. About 96 percent of the species in the Sanak Island food web were within two feeding links of a human palate, Dunne said.

The work by Maschner’s team documenting what the Aleuts ate over centuries, before discarding into garbage piles, opens a window on the past climate and marine life of the North Pacific.

Middens of ancient settlements on Sanak provide clues into the rise and fall of marine mammals, fish species and other sea life in the region. How? If the critter was flourishing, basically, its bones show up in trash. Humans have been a major player all along.

“One observation is clear — modern 25- to 50-year fisheries and climate data sets for the North Pacific region represent little of the dramatic shifts in climate, productivity, and human feedbacks that have occurred over the last 5,000 years,” Maschner and 13 co-authors wrote in a 2009 paper discussing the Sanak Island project.

“As such, at least for the last few thousands of years, there is no ‘natural’ North Pacific ecosystem without humans as one of the key species in that ecosystem.”

Another insight: Long-term climate shifts of the sort now whomping the North Pacific have probably shuffled the concentration of species many times in the past, including humans at the top of the food chain.

For instance, the crash of Steller sea lions in the western Aleutians seen since the 1970s appears to resemble ecological events triggered during earlier warm periods, Maschner and his team have argued. One occurred about 800 years ago and another peaked during the mid-1800s. For a seafaring people who needed six sea lion pelts to sew the skin for a single kayak, Maschner has said, a sea lion crash spells great difficulty. Some village sites temporarily lost 80 percent of their human population during these climatic shifts.

Overall, though, the Aleut people managed to ride out the vagaries of the North Pacific climate and marine ecosystem for eons, repeatedly rebounding and reoccupying sites. The Egyptian pyramids rose, and the Roman Empire fell, and Europe colonized the globe — all while the Aleuts continued to hunt, harvest and gather as key members of the local ecology.

“We know that the Aleut lived on this island for thousands of years without other species going extinct,” Dunne said here. “A super-generalist can co-exist with other species if it focuses on just a few of its possible prey at a time and switches prey regularly.”

“This is a natural behavior for predators. It’s stabilizing for the system because it allows populations to recover.”  

Contact Doug O'Harra at doug(at)alaskadispatch.com