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Posted January 11, 2000

Influences of Past and Future Climates on Atlantic Salmon

By George L. Jacobson Jr., Professor of Quaternary Biology, University of Maine

Populations of Atlantic salmon in New England are near the natural southern limit of the species. Because climate is continually changing, a critical question is whether variations in climate affected the natural populations in the past, and whether future warming will provide even greater challenges to restoration efforts.

Salmon's Range . . .

Atlantic salmon (Salmo salar) are distributed throughout northern forest ecosystems surrounding the North Atlantic Ocean. They range from Maine at the southern end through Maritime Canada, north to Greenland, and eastward to Scotland and Norway. The species requires the cool, well-oxygenated water typically found in streams of moderate to steep gradient.

Climate Variability . . .

Information about past climates comes from detailed scientific investigations of recent earth history. Geological and biological research involving lake sediments, ocean sediments, and thick ice deposits in places such as Greenland allows the following reconstruction: In northern New England, the climate for most of the past 10,000 years was warmer and drier than the present climate. Conversely, for much of the last 1000 years, and in particular in the recent cool period known as the Little Ice Age (ca. 1450 to 1850 AD), New England has been cooler and moister than at present. That cooling caused the forest of Maine to change significantly; for example, our spruce/fir forests became dominant in northern and eastern Maine only in the past 500 years, probably as a result of the cool Little Ice Age. These and other climate data demonstrate that Maine's climate has varied significantly over time. One important implication is that the fringe populations of salmon encountered by the early European settlers in New England may well have resulted from southward range expansion during the Little Ice Age. Prior to the past 500 years or so, salmon were likely absent from Maine, restricted to cooler regions to the north for most of the past 10,000 years.

Support from Archaeology . . .

The archeological record supports the hypothesis that salmon were either not present or not abundant in Maine prior to the Little Ice Age. Along Maine rivers, archaeological sites dating to the period prior to European settlement contain thousands of bones of several anadromous fish species (e.g., sturgeon Acipenser sp. and American shad Alosa sapidissima) that hatch in fresh water, mature in the open ocean, and return to our rivers to spawn. However, only a few large salmonid bones have been found among the many thousands of specimens recovered. In contrast, an archaeological dating to the 18th Century site from interior Maine has abundant remains of Atlantic salmon. Analysis of word origins in several native languages of the tribes in the northeastern U.S. suggests that Atlantic salmon was not of long-standing importance to those peoples. These lines of evidence support the hypothesis that the range of Atlantic salmon shifted southward or expanded in New England within the past several hundred years.

What of the Future? . . .

Maine's climate has become warmer during the past 150 years. Current climate models predict that even warmer conditions will occur as a result of human-induced increases in greenhouse gases. These observations suggest that the range limit of Atlantic salmon habitats may be driven northward as New England rivers become increasingly marginal.

For more information contact:

George Jacobson, Professor of Quaternary Studies, 207-581-2991, jacobson@maine.edu

Dr. Jacobson is a member of the Department of Biological Sciences and Director of the University of Maine Institute for Quaternary Studies. His research involves long-term changes in climate and their influences on forests and other natural ecosystems. His research has involved sites in Maine, Minnesota, Florida, Sweden, Chile, and other associated areas.

If you would like to receive addition copies of this white paper or any other papers in the series, please contact:

Judith Round, College of Natural Sciences, Forestry, and Agriculture, University of Maine, 5782 Winslow Hall, Orono, Maine 04469-5782

Telephone: (207) 581-3229; E-Mail: judy.round@umit.maine.edu

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