Cyclical Variations in the Return Migration of Scottish Salmon by Sea-age c.1790 to 1976

George, Anthony Frank (1982). Cyclical Variations in the Return Migration of Scottish Salmon by Sea-age c.1790 to 1976. MPhil thesis The Open University.



The thesis demonstrates by detailed statistics and factual
historical comment that the return-migration of the Atlantic salmon of Scotland has varied by sea-age periodically over the past two hundred years’ or so. The conclusion reached is that such periodic variations by sea-age are a natural characteristic of the salmon run.

The numerical return of the Scottish salmon consists of two
principal classes of fish: One that has spent a single winter in the sea after migrating as a smolt (’’grilse”), and the other that has spent one winter and a part of a second, or longer, in the sea (’’salmon”). Therefore a consideration of periodic variations by sea-age implies a statistical comparison of the numbers of grilse with the numbers of salmon for identical years. This is the method adopted in the thesis which also conforms with the historical method of recording catches.

The thesis identifies to the nearest approximate year or few
years the principal cycles of return-migration by sea-age between c.1790 and 1976. Such variations are of major significance to both the commercial and the sporting salmon fisheries.

Other properties of the return-migration are described and
discussed, including periodic variations in the seasonal timing of the-main migrations of salmon and grilse and periodically varying fish average weights, both important factors affecting the salmon fishery.

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