Andrew Crighton

Staff Writer

A study co-authored by Bruce Finney, professor in the department of biological sciences, has confirmed that native people captured and consumed ocean going salmon as a staple of their diet as far back as 11,500 years ago, the earliest date able to be confirmed in North America.

The study was a combination of excavation in the field and analysis done in the lab.

In the Upward Sun River Site in central Alaska, researchers found the remains of salmon and of human burials in association with a cooking hearth. There were two main questions about the bones that needed to be answered in order for the researchers to be make conclusions about the implications of having salmon remains at that date: to determine the species of the fish bones found, and to determine if they had been ocean going.

In order to determine the species, a DNA analysis was done to match the remains with the DNA they would be confirmed as, chum salmon. The second question was if these fish made it to the ocean and returned to spawn.

Occasionally due to any number of circumstances like landslides or glacial activity, a group of salmon can be locked inside of the freshwater ecosystem. Depending on the variety, it has the ability to adapt and live inside of that ecosystem without ever leaving the freshwater.   

“Freshwater fish populations at high latitudes like that aren’t super abundant,” said Finney, who specializes in oceanography, paleoclimate, paleoecology and paleoclimate change. “If it was freshwater salmon, it probably wouldn’t have been that big of a food source. You think of Alaska if you want to catch a lot of big fish; the fresh waters aren’t that productive though, but it is because of that ocean link.”

In order to determine if these fish were ocean going, the field researchers contacted Finney to ask him to help in the identification and interpretation of the results. Finney has developed and published papers on a way to determine if a salmon has left the freshwater ecosystem based on analyzing stable isotopes.

When salmon grow in the ocean, they take in many nutrients, namely nitrogen, which contain certain stable isotopes that aren’t found in the same levels in freshwater. Once the fish returns to the freshwater to spawn, it dies and the body decomposes leaving behind traces of those nutrients on the sediment layer of the river or stream at the time of that salmon run. By taking core samples of rivers, lakes and streams and analyzing a particular stable isotope in the nitrogen, the presence and size of salmon runs can be determined.

By adapting his existing research, Finney found that these 11,500-year-old salmon were in fact ocean going.

Because these bones were from ocean going fish, the researchers were able to infer that one of the staple food sources for the people who lived in the area at the time was the annual salmon run, providing a large resource to them, which may have helped with the migration of North America, south from Asia.

This study, published in the “Proceedings of the National Academy of Sciences,” had gained widespread media attention, and for one particular reason.

Many people assume that the people in the area ate salmon before this study. However, up until this point it has been very hard to provide evidence for that.

“Salmon bones do not preserve very well at all in geological or even archeological context, that’s why that paper is so important,” said Finney.

Salmon most often die in gravely stream beds, areas that are not productive to fossilization.

The fact that these bones were found in a cooking hearth can be viewed as both a blessing and a curse. Because they were cooked, it provides extremely strong evidence that people were indeed eating them, as well as essentially centralizing a mass of those hard to find remains. But cooking also damaged many of the bones to the point that the isotope Finney was looking for was not present.

Samples that were able to provide useable results were found and analyzed, which Finney attributes to the skill of the field researchers who discovered and developed the field site.

Another implication of the study shows how the range of wild salmon has been reduced through time, by factors such as climate change and development. The location that the field site was discovered at was described in the study as, “near the modern extreme edge of salmon habitat in central Alaska.”

Much of Finney’s work is targeted at the salmon population in both the present and the past, and understanding how it has changed.

“In this whole Pacific Rim area from Japan all the way to California where salmon are, or used to be,” said Finney. “It’s just another reminder to how significant they are to people and the ecosystem. Maybe there’s a little message that maybe we should try to not mess them up anymore.”