Historical rise of waterpower initiated the collapse of salmon stocks

Historical rise of waterpower initiated the collapse of salmon stocks

By H. J. R. Lenders, T. P. M. Chamuleau, A. J. Hendriks, R. C. G. M. Lauwerier, R. S. E. W. Leuven and W. C. E. P. Verberk

Scientific Reports 6, Article number: 29269 (2016)

Detail of a marginal miniature of a leaping salmon in a river in Munster. British Library MS Royal 13 B VIII f.23

Abstract: The collapse of Atlantic salmon (Salmo salar) stocks throughout North-Western Europe is generally ascribed to large-scale river regulation, water pollution and over-fishing in the 19th and 20th century. However, other causes have rarely been quantified, especially those acting before the 19th century. By analysing historical fishery, market and tax statistics, independently confirmed by archaeozoological records, we demonstrate that populations declined by up to 90% during the transitional period between the Early Middle Ages (c. 450–900 AD) and Early Modern Times (c. 1600 AD). These dramatic declines coincided with improvements in watermill technology and their geographical expansion across Europe. Our extrapolations suggest that historical Atlantic salmon runs must have once been very abundant indeed. The historical perspective presented here contributes to a better understanding of the primary factors that led to major declines in salmon populations. Such understanding provides an essential basis for the effective ecological rehabilitation of freshwater ecosystems.

Excerpt: In the Palaeo-Rhine catchment many watermills with vertical water wheels were in operation in the Middle Ages, in contrast to the much smaller horizontal water wheel mills, mostly operated in peripheral regions in Europe such as Ireland, Scotland and Scandinavia. Vertical water wheel mills are associated with hydropower dams and reservoirs that create conditions for sufficient fall for water to drive the water wheels. These dams allowed watermills to be constructed in streams with relatively low water flow. Improvements in construction techniques enabled mills to be constructed in increasingly larger, higher order rivers.

The use of watermills spread rapidly in the Palaeo-Rhine catchment from the 11th century onwards. In the Meuse catchment, mill presence peaks in the 18th century. In the Rhine catchment, a greater proportion of mills was constructed in earlier centuries. In both catchments, the number of newly constructed watermills declined sharply in the 20th century when other modes of power generation arose. While several watermills present in historical records no longer exist, they have had a lasting impact on streams, either in the form of extant dams or through geomorphologic alterations of the stream-bed and the stream valley.

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