Teppo Vehanen - Profile on 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]

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.

An Integrated Approach, 2013

Life in the ice lane: a review of the ecology of salmonids in winter

Annales Zoologici Fennici

Management of Fisheries in a Large Lake - for Fish and Fishermen

Cowx/Management, 2002

An Integrated Approach, 2013

Happamien sulfaattimaiden vesiensuojelumenetelmien ekologiset, taloudelliset ja sosiaaliset vaikutukset Kyrönjoen valuma-alueella

The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water d... more The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water discharge (simulating hydropeaking) but with a stable water-covered area were studied in six experimental stream channels, both during the winter and summer. Thirty fish were stocked into each channel, and the growth, body fat and movements of the fish were followed for about 2.5 months in each season. During the winter, no effect of hydropeaking was documented on performance or movement. In the summer, fish experiencing hydropeaking had lower body mass, lower body fat, and higher movement rates than the control fish. In general, effect sizes were small, and the rapid and frequent changes in water discharge and water level in the present study had small effects on the performance of juvenile Atlantic salmon. The cumulative long-term effect at the population level is unknown, but a reduced growth rate of 10% and a reduction in body fat of 16% in the hydropeaking experiments in the summer might to some extent translate into increased smolt age and lower overwintering survival.

Short-term regulation of hydro powerplants. Studies on the environmental effects

A. M ä ki-Pet ä ys and T. Vehanen, Finnish Game and Fisheries Research Inst., Oulu Game and Fishe... more A. M ä ki-Pet ä ys and T. Vehanen, Finnish Game and Fisheries Research Inst., Oulu Game and Fisheries Research, PO Box 413, Finland. Temporal coherence or spatial synchrony refers to the tendency of population, community or ecosystem dynamics to behave similarly among locations through time as a result of spatially-correlated environmental stochasticity (Moran eff ect), dispersal or trophic interactions. While terrestrial studies have treated synchrony mainly as a population-level concept, the majority of freshwater studies have focused on community-level patterns, particularly in lake planktonic communities. We used spatially and temporally hierarchical data on benthic stream invertebrates across six years, with three seasonal samples a year, in 11 boreal streams to assess temporal coherence at three spatial extents: 1) among regions (watersheds), 2) among streams within a region, and 3) among riffl es within a stream, using the average of correlation coeffi cients for stream/riffl e pairs across years. Our results revealed the primacy of strongly synchronized climatic factors (precipitation, air temperature) in inducing temporal coherence of macroinvertebrate assemblages across geographically distinct sites (i.e. Moran eff ect). Coherence tended to decrease with increasing spatial extent, but positive coherence was detected for most biological variables even at the largest extent (about 350 km). Th e generally high level of coherence refl ected the strong seasonality of boreal freshwater communities. A hydrologically exceptional year enhanced the synchrony of biological variables, particularly total macroinvertebrate abundance. Regionally low precipitation in that year led to a substantial decrease in benthic densities across a broad spatial extent, followed by a rapid post-drought recovery. Coherence at the among-riffl e (within-stream) extent was lower than expected, implying that local-scale habitat fi lters determine community dynamics at smaller spatial extents. Th us, temporal coherence of stream benthic communities appears to be controlled by partly diff erent processes at diff erent spatial scales.

Impacts of acid sulfate soils on river biota in Finnish rivers

Regulated Rivers: Research & Management, 1997

The Oulujoki, Iijoki and Kemijoki Rivers in northern Finland, all of them previously important ri... more The Oulujoki, Iijoki and Kemijoki Rivers in northern Finland, all of them previously important rivers for the fishing of migratory salmonids, were dammed for hydropower production in the 1940s-1960s. Some 20 years after the construction of the last power plant, the fish communities, fishing and the effects of brown trout (Salmo trutta m. lacustris) and rainbow trout (Oncorhynchus mykiss) stocking were studied in fifteen reservoirs, five in each of these rivers. Test fishing, echo sounding and fish tagging were used to collect descriptive information about the fish communities and the distribution and movements of fish. Catch statistics were used to estimate the yields and the fishing in the reservoirs. The results showed similarity in the fishing effort and the fish stocks in the reservoirs studied. Cyprinids, especially roach (Rutilus rutilus), were the most numerous species in the area. The hydroacoustic survey suggested that most of the fish occurred near to the river banks. Fishing in these reservoirs has recently increased, but it is mostly directed at predatory species rather than roach. The increase in the amount of fishing can partly be attributed to the stocking of rainbow trout of a takeable size (018-112 kg), which give good yields. Poor yields resulting from the previously standard stockings of brown trout smolts have been improved by stocking fish exceeding 30 cm in length. The results, however, show that stocking is not profitable in all the reservoirs. The future prospects for recreational rod fishing in the reservoirs are good, but improvements in the conditions for operating traps and gill nets are needed to optimize yields. This could include an intensive stocking of predatory fish, brown trout and rainbow trout.

Length at Release Affects Movement and Recapture of Lake-Stocked Brown Trout

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

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 ...

Journal of Fish Biology, 2003

Juvenile Atlantic salmon Salmo salar were shown experimentally to make adaptive behavioural decis... more Juvenile Atlantic salmon Salmo salar were shown experimentally to make adaptive behavioural decisions as a short-term response to changes in food availability and predation risk. Restricted food availability caused an increase in activity, whereas activity was decreased under predation threat. Although changes in activity were not more pronounced among the hungermotivated fish, suggesting that they were not balancing risk and hunger, hungrier fish spent less time in refuges in the presence of a predator, indicating that they were more willing to take risks than satiated fish. Aggressive interactions among juvenile Atlantic salmon were decreased by predation threat, but were highest when predators were absent and food was abundant.

Predation Threat Affects Behaviour and Habitat Use by Hatchery Brown Trout (Salmo Trutta L.) Juveniles

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

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). ...

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]

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.

An Integrated Approach, 2013

Life in the ice lane: a review of the ecology of salmonids in winter

Annales Zoologici Fennici

Management of Fisheries in a Large Lake - for Fish and Fishermen

Cowx/Management, 2002

An Integrated Approach, 2013

Happamien sulfaattimaiden vesiensuojelumenetelmien ekologiset, taloudelliset ja sosiaaliset vaikutukset Kyrönjoen valuma-alueella

The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water d... more The performance and movements of juvenile Atlantic salmon Salmo salar exposed to variable water discharge (simulating hydropeaking) but with a stable water-covered area were studied in six experimental stream channels, both during the winter and summer. Thirty fish were stocked into each channel, and the growth, body fat and movements of the fish were followed for about 2.5 months in each season. During the winter, no effect of hydropeaking was documented on performance or movement. In the summer, fish experiencing hydropeaking had lower body mass, lower body fat, and higher movement rates than the control fish. In general, effect sizes were small, and the rapid and frequent changes in water discharge and water level in the present study had small effects on the performance of juvenile Atlantic salmon. The cumulative long-term effect at the population level is unknown, but a reduced growth rate of 10% and a reduction in body fat of 16% in the hydropeaking experiments in the summer might to some extent translate into increased smolt age and lower overwintering survival.

Short-term regulation of hydro powerplants. Studies on the environmental effects

A. M ä ki-Pet ä ys and T. Vehanen, Finnish Game and Fisheries Research Inst., Oulu Game and Fishe... more A. M ä ki-Pet ä ys and T. Vehanen, Finnish Game and Fisheries Research Inst., Oulu Game and Fisheries Research, PO Box 413, Finland. Temporal coherence or spatial synchrony refers to the tendency of population, community or ecosystem dynamics to behave similarly among locations through time as a result of spatially-correlated environmental stochasticity (Moran eff ect), dispersal or trophic interactions. While terrestrial studies have treated synchrony mainly as a population-level concept, the majority of freshwater studies have focused on community-level patterns, particularly in lake planktonic communities. We used spatially and temporally hierarchical data on benthic stream invertebrates across six years, with three seasonal samples a year, in 11 boreal streams to assess temporal coherence at three spatial extents: 1) among regions (watersheds), 2) among streams within a region, and 3) among riffl es within a stream, using the average of correlation coeffi cients for stream/riffl e pairs across years. Our results revealed the primacy of strongly synchronized climatic factors (precipitation, air temperature) in inducing temporal coherence of macroinvertebrate assemblages across geographically distinct sites (i.e. Moran eff ect). Coherence tended to decrease with increasing spatial extent, but positive coherence was detected for most biological variables even at the largest extent (about 350 km). Th e generally high level of coherence refl ected the strong seasonality of boreal freshwater communities. A hydrologically exceptional year enhanced the synchrony of biological variables, particularly total macroinvertebrate abundance. Regionally low precipitation in that year led to a substantial decrease in benthic densities across a broad spatial extent, followed by a rapid post-drought recovery. Coherence at the among-riffl e (within-stream) extent was lower than expected, implying that local-scale habitat fi lters determine community dynamics at smaller spatial extents. Th us, temporal coherence of stream benthic communities appears to be controlled by partly diff erent processes at diff erent spatial scales.

Impacts of acid sulfate soils on river biota in Finnish rivers

Regulated Rivers: Research & Management, 1997

The Oulujoki, Iijoki and Kemijoki Rivers in northern Finland, all of them previously important ri... more The Oulujoki, Iijoki and Kemijoki Rivers in northern Finland, all of them previously important rivers for the fishing of migratory salmonids, were dammed for hydropower production in the 1940s-1960s. Some 20 years after the construction of the last power plant, the fish communities, fishing and the effects of brown trout (Salmo trutta m. lacustris) and rainbow trout (Oncorhynchus mykiss) stocking were studied in fifteen reservoirs, five in each of these rivers. Test fishing, echo sounding and fish tagging were used to collect descriptive information about the fish communities and the distribution and movements of fish. Catch statistics were used to estimate the yields and the fishing in the reservoirs. The results showed similarity in the fishing effort and the fish stocks in the reservoirs studied. Cyprinids, especially roach (Rutilus rutilus), were the most numerous species in the area. The hydroacoustic survey suggested that most of the fish occurred near to the river banks. Fishing in these reservoirs has recently increased, but it is mostly directed at predatory species rather than roach. The increase in the amount of fishing can partly be attributed to the stocking of rainbow trout of a takeable size (018-112 kg), which give good yields. Poor yields resulting from the previously standard stockings of brown trout smolts have been improved by stocking fish exceeding 30 cm in length. The results, however, show that stocking is not profitable in all the reservoirs. The future prospects for recreational rod fishing in the reservoirs are good, but improvements in the conditions for operating traps and gill nets are needed to optimize yields. This could include an intensive stocking of predatory fish, brown trout and rainbow trout.

Length at Release Affects Movement and Recapture of Lake-Stocked Brown Trout

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

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 ...

Journal of Fish Biology, 2003

Juvenile Atlantic salmon Salmo salar were shown experimentally to make adaptive behavioural decis... more Juvenile Atlantic salmon Salmo salar were shown experimentally to make adaptive behavioural decisions as a short-term response to changes in food availability and predation risk. Restricted food availability caused an increase in activity, whereas activity was decreased under predation threat. Although changes in activity were not more pronounced among the hungermotivated fish, suggesting that they were not balancing risk and hunger, hungrier fish spent less time in refuges in the presence of a predator, indicating that they were more willing to take risks than satiated fish. Aggressive interactions among juvenile Atlantic salmon were decreased by predation threat, but were highest when predators were absent and food was abundant.

Predation Threat Affects Behaviour and Habitat Use by Hatchery Brown Trout (Salmo Trutta L.) Juveniles

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

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). ...