Historical ecology of anadromous houting (Coregonus oxyrinchus / C. lavaretus) in the Rhine-Meuse delta

Houting ( Coregonus oxyrinchus / C. lavaretus ) is a facultative anadromous fish species that gradually declined and finally extirpated from the Rhine-Meuse delta during the first half of the 20 th century, together with several other migratory fish species. We examined >10k multi-characteristic historic sources of potential information on houting, like paintings and newspaper articles, to reconstruct historic presence, abundance and environmental history of houting. Our results showed that houting was present in the Rhine-Meuse delta at least from the early 13 th century and started to decline from the second half of the 19 th century, decades earlier than stated in previous studies. The strong decline in houting abundance coincided with large morphological changes and intensifying river fisheries. This trend preceded the strong deterioration of the chemical water quality and the period in which river connectivity was lost by the building of barriers, like weirs and dams. The recent recovery of houting in the Netherlands coincided with a strong improvement of chemical water quality and restocking programs in NW-Europe. Since river fisheries are virtually absent to date, and the river morphology is still highly artificial, we argue that houting suffered mainly from fisheries in the period 1850-1940 and that its recovery was hampered by a poor chemical water quality and not by a loss of river connectivity. Our multi-source, single-species approach provided greater insight into the human induced impacts on the decline and recovery of a keystone migratory fish species. Our study supports the development of targeted, species-specific actions to address bottlenecks hindering the successful recovery of migratory fish populations in European rivers.