University of Oulu

Ecology and impacts of nonnative salmonids with special reference to brook trout (Salvelinus fontinalis Mitchill) in North Europe

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Author: Korsu, Kai1,2
Organizations: 1University of Oulu, Faculty of Science, Department of Biology
2Finnish Game and Fisheries Research Institute, Kainuu Fisheries Research
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.6 MB)
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Language: English
Published: 2008
Publish Date: 2008-10-06
Thesis type: Doctoral Dissertation
Defence Note: Academic dissertation to be presented, with the assent of the Faculty of Science of the University of Oulu, for public defence in Kuusamonsali (Auditorium YB210), Linnanmaa, on October 16th, 2008, at 12 noon
Reviewer: Professor Per-Arne Amundsen
Professor Larry Greenberg


My main objectives in this thesis were to explore general patterns and mechanisms driving salmonid invasions globally and, more specifically, to examine the invasion dynamics and impacts of the North American brook trout in North European stream systems.

Non-native salmonids have often spread extensively and caused many harmful impacts on their native counterparts. Among the three globally introduced salmonids, the European brown trout appeared as the ’worst’ alien species (strongest impact on native fish), followed by the North American rainbow trout and brook trout.

Brook trout, which is widely established in European streams, was found to be a non-aggressive species. Moreover, the growth of brown trout was unaffected by brook trout, indicating negligible interspecific interactions between the two species. Habitat niche segregation between brook trout and brown trout was evident, with brook trout occupying mainly low-velocity pool habitats, whereas brown trout resided in fast-flowing riffles. At the river-wide scale, brook trout occurred mainly in small, slightly acid headwater streams, whereas brown trout was found primarily in larger downstream river sections. Evidently, North European streams with a very low number of native fish species offer underutilized niche space for tolerant headwater specialists such as brook trout.

However, the habitat niche filled by brook trout was not completely vacant, as brown trout co-occurred with brook trout in numerous small and mid-sized (3–16 m wide) streams. In these streams, brown trout reproduction was negligible presumably related to the presence of brook trout. Brook trout had also increased in density relative to brown trout during the 10-yr study period (1994 vs. 2004). Moreover, the growth rate and population densities of brook trout were high and the species had spread extensively towards the upmost headwater streams during the 10-yr study period. Thus, harmful effects on the native brown trout by brook trout are likely to occur in the core habitat of the invader, i.e. headwater streams, leaving populations of the native species unaffected elsewhere. Due to the high conservation value of the potentially impacted populations of brown trout, I strongly caution against further stocking of brook trout in European watersheds.

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Series: Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
ISSN-E: 1796-220X
ISBN: 978-951-42-8864-7
ISBN Print: 978-951-42-8863-0
Issue: 512
Copyright information: © University of Oulu, 2008. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.