Teppo Vehanen - Academia.edu (original) (raw)
Papers by Teppo Vehanen
The growing concern on declining salmonid populations has resulted in numerous restoration projec... more The growing concern on declining salmonid populations has resulted in numerous restoration projects with variable responses worldwide. In this spatially replicated multiyear study, we assessed the long-term (12 years postrestoration) effects of in-stream habitat restoration (i.e., addition of boulders or large woody debris (LWD) together with boulders) on densities of three age-classes of juvenile brown trout (Salmo trutta) in six forest streams in northern Finland. LWD combined with boulders was more beneficial, particularly for the larger trout (age-2 and older), than were boulder structures alone, indicating that the more diverse habitat created by LWD may have provided a safeguard against drought for the larger fish. Density of age-0+ trout showed a significant long-term increase in boulder-restored sections, providing evidence that log structures may need to be complemented by stony enhancement structures to guarantee the availability of suitable stream habitat for all trout age-classes. As trout densities are known to exhibit inherently wide interannual variability that tracks climatically induced hydrological variation, long-term postrestoration monitoring that encompasses extreme hydrological events is critical for evaluating the success of restoration projects. Résumé : La préoccupation de plus en plus grande que constitue le déclin des salmonidés s'est traduite par de nombreux projets de restauration dans le monde entier dont les effets sont variables. Dans une étude sur plusieurs années répétée dans l'espace, nous avons évalué les effets a ` long terme (après 12 ans) de la restauration d'habitats de cours d'eau (p. ex. ajout de blocs rocheux ou de débris ligneux grossiers (DLG) jumelés a ` des blocs) sur les densités de trois classes d'âge de truites de mer (Salmo trutta) juvéniles dans six cours d'eau forestiers du nord de la Finlande. Les DLG combinés a ` des blocs étaient plus bénéfiques, particu-lièrement pour les truites plus grandes (2 ans et plus) que les structures constituées uniquement de blocs, ce qui indique que les habitats plus variés créés par les DLG pourraient offrir une protection contre la sécheresse aux poissons de plus grande taille. La densité de truites d'âge 0+ année présentait une augmentation a ` long terme significative dans les tronçons restaurés avec des blocs, indiquant que des structures rocheuses pourraient devoir être ajoutées aux structures de billots pour garantir la dis-ponibilité d'habitats de cours d'eau convenables pour toutes les classes d'âge de truites. Comme il est établi que la densité des truites présente en soi une grande variabilité interannuelle qui suit les variations hydrologiques induites par le climat, une surveillance a ` long terme post-restauration qui couvre des évènements hydrologiques extrêmes est particulièrement importante pour assurer l'efficacité de projets de restauration. [Traduit par la Rédaction]
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Collated electrofishing data from wade-able riffles of boreal rivers in Finland revealed a substa... more Collated electrofishing data from wade-able riffles of boreal rivers in Finland revealed a substantial shift in the fish assemblage composition, accompanied by a decline in total fish density and a reduction in species richness from early summer to late autumn. As the major changes in fish assemblages, the density of cyprinids decreased sharply from June towards autumn, whereas salmonids peaked in September. These shifts were considered to originate mainly from spawning migrations, fish movements to winter refuge habitat and other temperature-related responses of rheophilic versus eurytopic fish species. Temporal change in fish assemblages induced a prominent variation in the monthly fish-based index values used for bioassessment. The proportion of sampled sites classified as high or good in ecological status within the Water Framework Directive (WFD) based on fish increased from 25.9% in July to 68.3% in October. These results, combined with the observed timing of young of the year (0?) fish recruitment to electrofishing catch, suggest that sampling of fish in boreal rivers for WFD monitoring should be restricted to a considerably shorter period than the prevailing practice in order to avoid temporal bias.
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An Integrated Approach, 2013
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Annales Zoologici Fennici
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Regulated Rivers: Research & Management, 1997
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North American Journal of Fisheries Management, 2003
The effect of length (total length = 15-50 cm) at release on the yield and recapture of stocked b... more The effect of length (total length = 15-50 cm) at release on the yield and recapture of stocked brown trout Salmo trutta was examined by tagging experiments in a large boreal lake, Lake Oulujärvi in Finland (928 km). The time the fish spent in the lake before harvesting and the size of the area from which they were harvested diminished
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Lakes & Reservoirs: Research & Management, 2008
... 140, 91–116. Web of Science® Times Cited: 49. Franklin RF & Smith LL (196... more ... 140, 91–116. Web of Science® Times Cited: 49. Franklin RF & Smith LL (1963) Early life history of northern pike, Esox lucius L., with special reference to the factors influencing the numerical strength of year-classes. ... Kurkilahti M., Appelberg M., Hesthagen T. & Rask M. (2002 ...
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Journal of Fish Biology, 2003
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Hydrobiologia, 2000
The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juve... more The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juveniles were studied in four indoor and six outdoor experimental channels. Northern pike (Esox lucius L.) was used as a predator. Brown trout were more active during the night compared to day, but in the presence of pike the increase in activity was less
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Hydrobiologia, 2005
... To describe the physical conditions along the shore, the water depth, current velocity and su... more ... To describe the physical conditions along the shore, the water depth, current velocity and sub-strate size were measured from three lines (1, 2 and 3 m from the shoreline) across each electrofishing area (3 in each of the 3 sampling areas). ...
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The growing concern on declining salmonid populations has resulted in numerous restoration projec... more The growing concern on declining salmonid populations has resulted in numerous restoration projects with variable responses worldwide. In this spatially replicated multiyear study, we assessed the long-term (12 years postrestoration) effects of in-stream habitat restoration (i.e., addition of boulders or large woody debris (LWD) together with boulders) on densities of three age-classes of juvenile brown trout (Salmo trutta) in six forest streams in northern Finland. LWD combined with boulders was more beneficial, particularly for the larger trout (age-2 and older), than were boulder structures alone, indicating that the more diverse habitat created by LWD may have provided a safeguard against drought for the larger fish. Density of age-0+ trout showed a significant long-term increase in boulder-restored sections, providing evidence that log structures may need to be complemented by stony enhancement structures to guarantee the availability of suitable stream habitat for all trout age-classes. As trout densities are known to exhibit inherently wide interannual variability that tracks climatically induced hydrological variation, long-term postrestoration monitoring that encompasses extreme hydrological events is critical for evaluating the success of restoration projects. Résumé : La préoccupation de plus en plus grande que constitue le déclin des salmonidés s'est traduite par de nombreux projets de restauration dans le monde entier dont les effets sont variables. Dans une étude sur plusieurs années répétée dans l'espace, nous avons évalué les effets a ` long terme (après 12 ans) de la restauration d'habitats de cours d'eau (p. ex. ajout de blocs rocheux ou de débris ligneux grossiers (DLG) jumelés a ` des blocs) sur les densités de trois classes d'âge de truites de mer (Salmo trutta) juvéniles dans six cours d'eau forestiers du nord de la Finlande. Les DLG combinés a ` des blocs étaient plus bénéfiques, particu-lièrement pour les truites plus grandes (2 ans et plus) que les structures constituées uniquement de blocs, ce qui indique que les habitats plus variés créés par les DLG pourraient offrir une protection contre la sécheresse aux poissons de plus grande taille. La densité de truites d'âge 0+ année présentait une augmentation a ` long terme significative dans les tronçons restaurés avec des blocs, indiquant que des structures rocheuses pourraient devoir être ajoutées aux structures de billots pour garantir la dis-ponibilité d'habitats de cours d'eau convenables pour toutes les classes d'âge de truites. Comme il est établi que la densité des truites présente en soi une grande variabilité interannuelle qui suit les variations hydrologiques induites par le climat, une surveillance a ` long terme post-restauration qui couvre des évènements hydrologiques extrêmes est particulièrement importante pour assurer l'efficacité de projets de restauration. [Traduit par la Rédaction]
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Collated electrofishing data from wade-able riffles of boreal rivers in Finland revealed a substa... more Collated electrofishing data from wade-able riffles of boreal rivers in Finland revealed a substantial shift in the fish assemblage composition, accompanied by a decline in total fish density and a reduction in species richness from early summer to late autumn. As the major changes in fish assemblages, the density of cyprinids decreased sharply from June towards autumn, whereas salmonids peaked in September. These shifts were considered to originate mainly from spawning migrations, fish movements to winter refuge habitat and other temperature-related responses of rheophilic versus eurytopic fish species. Temporal change in fish assemblages induced a prominent variation in the monthly fish-based index values used for bioassessment. The proportion of sampled sites classified as high or good in ecological status within the Water Framework Directive (WFD) based on fish increased from 25.9% in July to 68.3% in October. These results, combined with the observed timing of young of the year (0?) fish recruitment to electrofishing catch, suggest that sampling of fish in boreal rivers for WFD monitoring should be restricted to a considerably shorter period than the prevailing practice in order to avoid temporal bias.
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An Integrated Approach, 2013
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Annales Zoologici Fennici
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Cowx/Management, 2002
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An Integrated Approach, 2013
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Regulated Rivers: Research & Management, 1997
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North American Journal of Fisheries Management, 2003
The effect of length (total length = 15-50 cm) at release on the yield and recapture of stocked b... more The effect of length (total length = 15-50 cm) at release on the yield and recapture of stocked brown trout Salmo trutta was examined by tagging experiments in a large boreal lake, Lake Oulujärvi in Finland (928 km). The time the fish spent in the lake before harvesting and the size of the area from which they were harvested diminished
Bookmarks Related papers MentionsView impact
Lakes & Reservoirs: Research & Management, 2008
... 140, 91–116. Web of Science® Times Cited: 49. Franklin RF & Smith LL (196... more ... 140, 91–116. Web of Science® Times Cited: 49. Franklin RF & Smith LL (1963) Early life history of northern pike, Esox lucius L., with special reference to the factors influencing the numerical strength of year-classes. ... Kurkilahti M., Appelberg M., Hesthagen T. & Rask M. (2002 ...
Bookmarks Related papers MentionsView impact
Journal of Fish Biology, 2003
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Hydrobiologia, 2000
The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juve... more The effect of predation threat on behaviour and habitat use by brown trout (Salmo trutta L.) juveniles were studied in four indoor and six outdoor experimental channels. Northern pike (Esox lucius L.) was used as a predator. Brown trout were more active during the night compared to day, but in the presence of pike the increase in activity was less
Bookmarks Related papers MentionsView impact
Hydrobiologia, 2005
... To describe the physical conditions along the shore, the water depth, current velocity and su... more ... To describe the physical conditions along the shore, the water depth, current velocity and sub-strate size were measured from three lines (1, 2 and 3 m from the shoreline) across each electrofishing area (3 in each of the 3 sampling areas). ...
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