Aki Mäki-Petäys

Twenty years of stream restoration in Finland: little response by benthic macroinvertebrate communities

The primary focus of many in-stream restoration projects is to enhance habitat diversity for salmonid fishes, yet the lack of properly designed monitoring studies, particularly ones with pre-restoration data, limits any attempts to assess whether restoration has succeeded in improving salmonid habitat. Even less is known about the impacts of fisheries-related restoration on other, non-target biota. We examined how restoration aiming at the enhancement of juvenile brown trout (Salmo trutta L.) affects benthic macroinvertebrates, using two separate data sets: (1) a before-after-control-impact (BACI) design with three years before and three after restoration in differently restored and control reaches of six streams; and (2) a space-time substitution design including channelized, restored, and near-natural streams with an almost 20-year perspective on the recovery of invertebrate communities. In the BACI design, total macroinvertebrate density differed significantly from before to after restoration. Following restoration, densities decreased in all treatments, but less so in the controls than in restored sections. Taxonomic richness also decreased from before to after restoration, but this happened similarly in all treatments. In the long-term comparative study, macroinvertebrate species richness showed no difference between the channel types. Community composition differed significantly between the restored and natural streams, but not between restored and channelized streams. Overall, the in-stream restoration measures used increased stream habitat diversity but did not enhance benthic biodiversity. While many macroinvertebrates may be dispersal limited, our study sites should not have been too distant to reach within almost two decades. A key explanation for the weak responses by macroinvertebrate communities may have been historical. When Fennoscandian streams were channelized for log floating, the loss of habitat heterogeneity was only partial. Therefore, habitat may not have been limiting the macroinvertebrate communities to begin with. Stream restoration to support trout fisheries has strong public acceptance in Finland and will likely continue to increase in the near future. Therefore, more effort should be placed on assessing restoration success from a biodiversity perspective using multiple organism groups in both stream and riparian ecosystems.

Microhabitat Use by Age-0 Brown Trout and Grayling: Seasonal Responses to Streambed Restoration under Different Flows

Abstract We examined microhabitat selection by age-0 brown trout Salmo trutta and grayling Thymallus thymallus in experimental flumes with channelized (monotonic configuration and low amount of stones) or restored (highly heterogenous substrate) streambed structures at low and high flows and at different times of year. Both brown trout and grayling used higher water velocities in summer high flows. Both species also occupied higher-velocity microhabitats in channelized than in restored flumes, but for grayling this difference was significant only in summer. Overall, brown trout used lower water velocities than grayling. In winter and in high-flow treatments, brown trout were more susceptible to downstream displacement in channelized compared with restored flumes. For grayling, the effect of flume type occurred only in winter when fish were located further downstream in channelized flumes. Both species were more aggregated in winter. Brown trout also exhibited a different spatial pattern among the flume ty...

Short sea migration and precocious maturation in reared Atlantic salmon post-smolts in the northern Baltic Sea

Short sea migration and precocious maturation in reared Atlantic salmon post-smolts in the northern Baltic Sea Panu Orell*, Jaakko Erkinaro, Mikko Kiljunen, Jyrki Torniainen, Tapio Sutela, Mikko Jaukkuri, and Aki Mäki-Petäys Natural Resources Institute Finland, University of Oulu, PO Box 413, Oulu FI 90014, Finland Department of Biological and Environmental Science, University of Jyvaskyla, PO Box 35, Jyvaskyla FI 40014, Finland Natural History Museum, University of Jyvaskyla, PO Box 35, Jyvaskyla FI 40014, Finland *Corresponding author: tel: þ358 405305830; e-mail: panu.orell@luke.fi

Seasonal shift in boreal riverine fish assemblages and associated bias in bioassessment

Collated electrofishing data from wadeable 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.

Impacts of Water Quality and Hand-Picking of Dead Eggs on the Survival of Brown Trout and Atlantic Salmon Eggs

Abstract The effect of water source and removal of dead eggs by hand on egg survival of brown trout Salmo trutta and Atlantic salmon S. salar was studied experimentally in a hatchery trial, which started from fertilization in October and lasted until egg eye-up in early March; no antifungal chemical treatments were used. The experimental treatments were water source (surface water, filtered surface water, or groundwater), species, and hand-picking of dead eggs (used, not used); we used four replicates per treatment, resulting in 48 batches. Incubation of eggs in groundwater yielded higher egg survival to eye-up than incubation in surface water or filtered surface water. Hand-picking of dead eggs enhanced survival of eggs incubated in surface water but not those incubated in groundwater. The best combination for egg survival in both species was the use of groundwater incubation without hand-picking of dead eggs.