INTRO: Fishermen accustomed to the quick boom-then-bust of Alaska's salmon runs may wish they were born in a different time—about 800 years ago, to be exact. As Doug Schneider reports in this week's Arctic Science Journeys Radio, scientists studying Alaska lakes have found evidence that the state's salmon booms once lasted centuries, not the mere decades seen today.
STORY: Alaska and Canadian scientists published their results in the April 18 issue of the journal Nature. They found that sockeye salmon runs to Alaska once rode waves of abundance lasting centuries. The most recent long-term boom began in the year 1200 and lasted until commercial fishing began in earnest in the 1900s. Bruce Finney is the study's lead author and a marine scientist at the University of Alaska Fairbanks Institute of Marine Science.
FINNEY: "In this present study, we're going back a little over 2,000 years. What we found in this study was that some of these periods of high and low abundance could be sustained for hundreds of years, not just several decades."
To reach their conclusions, scientists studied cores of mud taken from the bottom of two lakes on Alaska's Kodiak Island. The mud contained traces of the stable nitrogen isotope, N15, released into the lakes by salmon that died and decayed after spawning. While some of that nitrogen ended up trapped forever in the sediment, much of it nourished the growth of algae called diatoms. Researchers dated the mud layers using carbon dating techniques and known events such as volcanic eruptions that left ash in the mud. They then analyzed the abundance of nitrogen and diatoms in the layers to estimate the relative size of ancient salmon runs to the lakes. John Smol is a co-author of the study and a biologist at Queen's University in Ontario, Canada.
SMOL: " Since the carcasses give a very large part of the nitrogen and phosphorous into these lakes, we reasoned with Bruce that we could use diatoms—in addition to nitrogen isotopes—to reconstruct past nutrient levels. The argument being that we have higher nutrient levels, we would have more dead carcasses."
Using these techniques, the researchers say salmon runs rose and fell on timescales unheard of today. Of course what went up, eventually came down. In the case of salmon, the busts also lasted centuries. In one such bust, from about 100 BC to 800 AD, the number of salmon returning to Alaska lakes plummeted, according to co-author and graduate student Irene Gregory-Eaves of Queen's University.
GREGORY-EAVES: "If you look during the period around the time of Christ, the N15 levels were down much lower, so we're looking at substantially less than several hundred thousand (salmon)."
While salmon runs flourished in Alaska, other fish species declined in waters farther south. The finding lends support to the belief that fish stocks in Alaska rise and fall in trends opposite those of species along the U.S. West Coast.
Their research was funded by the National Science Foundation, the Alaska Sea Grant Program at the University of Alaska Fairbanks, and the National Oceanic and Atmospheric Administration's Auke Bay Laboratory in Juneau, Alaska.
The scientists also say their data supports the belief that salmon upswings influenced the development of Alaska's coastal Native cultures. Finney says evidence found at archeological sites on Kodiak Island shows the island's indigenous groups further developed fishing gear and began using salmon more frequently from 800 AD through 1200 AD, a time when salmon were more abundant.
FINNEY: "Since the Native people living along the coast heavily depended on salmon, the changes in the salmon were in fact influencing some of their cultural means, such as the type of hunting and fishing gear they used for subsistence. And so at a couple of these times when salmon changed abruptly, we see that that seems to coincide with when Native people relied more and more on marine mammals during low salmon periods to about 800 years ago, when salmon came back in higher numbers. Then all of a sudden the archeological data shows, 'Wow,' they shifted to relying way more heavily on salmon."
Finney says learning how the environment affected past salmon runs may help researchers predict how salmon might respond to future environmental changes. He and his colleagues aren't new to the study of ancient salmon runs. Two years ago, the team published in the journal Science the results of research on salmon runs going back 300 years. They next plan to reconstruct salmon runs going back to the end of the last major ice age, some 15,000 years ago, a time when salmon are thought to have colonized North Pacific watersheds as glaciers retreated.
OUTRO: This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program and the University of Alaska Fairbanks. I'm Doug Schneider.
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Thanks to the following individuals for help preparing this script:
John P. Smol
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks. The shortcut to our ASJ news home page is www.asjnews.org.
URL for this page is http://seagrant.uaf.edu/news/
Related Web sites
Alaska salmon booms once lasted centuries—Sea Grant news release
Climate change, fishing, alter salmon abundance—Science 10/26/2000
Why Salmon Boom, Then Bust—Arctic Science Journeys Radio
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