The potential influence of Atlantic salmon Salmo salar and brown trout Salmo trutta on density and breeding of the white‐throated dipper Cinclus cinclus |
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Authors: | Anna L. K. Nilsson Jan Henning L'Abée‐Lund L. Asbjørn Vøllestad Kurt Jerstad Bjørn Mejdell Larsen Ole Wiggo Røstad Svein Jakob Saltveit Thomas Skaugen Nils C. Stenseth Bjørn Walseng |
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Affiliation: | 1. Department of Biosciences, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, Oslo, Norway;2. Norwegian Water Resource and Energy Directorate, Oslo, Norway;3. Jerstad Viltforvaltning, Mandal, Norway;4. Norwegian Institute for Nature Research, Trondheim, Norway;5. Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, ?s, Norway;6. Freshwater and Inland Fisheries Laboratory, Natural History Museum, University of Oslo, Oslo, Norway;7. Norwegian Institute for Nature Research, Oslo, Norway |
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Abstract: | Interactions between birds and fish are often overlooked in aquatic ecosystems. We studied the influence of Atlantic salmon and brown trout on the breeding population size and reproductive output of the white‐throated dipper in a Norwegian river. Acidic precipitation led to the extinction of salmon, but salmon recolonized after liming was initiated in 1991. We compared the dipper population size and reproductive output before (1978–1992) and after (1993–2014) salmon recolonization. Despite a rapid and substantial increase in juvenile salmon, the breeding dipper population size and reproductive output were not influenced by juvenile salmon, trout, or total salmonid density. This might be due to different feeding strategies in salmonids and dippers, where salmonids are mainly feeding on drift, while the dipper is a benthic feeder. The correlation between the size of the dipper population upstream and downstream of a salmonid migratory barrier was similar before and after recolonization, indicating that the downstream territories were not less attractive after the recolonization of salmon. Upstream dipper breeding success rates declined before the recolonization event and increased after, indicating improved water quality due to liming, and increasing invertebrate prey abundances and biodiversity. Surprisingly, upstream the migratory barrier, juvenile trout had a weak positive effect on the dipper population size, indicating that dippers may prey upon small trout. It is possible that wider downstream reaches might have higher abundances of alternative food, rending juvenile trout unimportant as prey. Abiotic factors such as winter temperatures and acidic precipitation with subsequent liming, potentially mediated by prey abundance, seem to play the most important role in the life history of the dipper. |
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Keywords: | birds breeding predators river salmonids |
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