other stream, occurs, but only occasionally. For example, Penobscot River salmon show more than 98% fidelity to the home stream (Baum 1997).

Distribution

Atlantic salmon are distributed from about 40° N, northward, on both sides of the Atlantic Ocean. In Europe, wild salmon breed from western Russia to Iceland and south to northern Spain; on the western side, wild breeding populations are found from Labrador to Maine. These distributions have been influenced by geological changes, including ice ages (MacCrimmon and Gots 1979). Populations in the United States probably date from the end of the last ice age 10,000 years ago. Atlantic salmon were probably present in all watersheds from the Hudson River in New York north to the St. Croix River, the Canadian border (Kendall 1935). Atlantic salmon once occupied 34 rivers and streams in Maine (Beland 1984). Today, wild Atlantic salmon populations in the United States are found only in Maine,2 from the lower Kennebec River in the southwest to the Canadian border.

Maine’s salmon take part in extensive marine migrations, including movements to the waters off western Greenland (Friedland 1994), where they become a small portion of a large mixed-stock complex of salmon from both European and North American sources. Unlike Atlantic salmon populations across the Canadian border from Maine, where 1SW fish are common among spawning adults, about 94% of adults returning to Maine are 2SW fish (USASAC 1999). Thus, the average body size of Maine adults is larger than Canadian adults. Because spawning populations of Maine salmon include several age groups (especially 2SW and 3SW adults but also precocious mature parr3), there is considerable exchange of genetic material across age classes (cohorts).

Atlantic salmon spawn in freshwater streams on both sides of the Atlantic (Figure 2). The oceanic fishery in recent years has been concentrated to the west of Greenland, where fish from North America and Europe are encountered (Reddin andFriedland 1999). Natural movement (straying) of spawning

2  

Many Atlantic salmon have escaped from farms off the west coast of North America and concern has been expressed about their becoming established there (e.g., Volpe et al. 2001). Although adult Atlantic salmon have been observed in streams there, they are not wild and have not become established.

3  

Parr are young salmon growing in fresh water. Precociously mature parr are young males that spawn without first migrating to the sea.



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