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River restoration offers the potential to enhance biological integrity, often measured as fish population changes. We used a meta-analytical approach to synthesize density responses to in-stream habitat restoration by young-of-the year (YOY) brown trout and Atlantic salmon in 28 rivers (overall 32 restoration projects) in Finland. We also examined which local and watershed-scale factors most influenced restoration success. Finally, we conducted an expert survey to obtain an independent estimate of a sufficient density enhancement for restoration to be considered successful. Despite strong context-dependency, habitat restoration had an overall positive effect on YOY salmonid density. When compared to target levels derived from the expert survey, density responses mainly reached the minimum expected success rate, but remained short of the level considered to reflect distinct success. Variability in restoration responses of trout was linked mainly to river size, predominant geology, water quality and potential interspecific competition (trout vs. European bullhead). Fishing mortality tended to obscure positive effects of restoration and stocking by YOY fish affected negatively trout’s response to restoration, supporting a shift towards self-sustainable schemes in fisheries management. These results imply that habitat restoration is a useful approach for improving the ecological and conservational status of salmonid populations in boreal rivers. To further improve the success rate, and thereby public acceptance, of restorations they need to be complemented by other management measures that enhance the potential for the recovery of threatened salmonid populations. peerReviewed

Two small-scale surveys were conducted in a small river to examine the effects of physical habitat characteristics, spatial spawning redd distribution and abundance of older juveniles on the Atlantic salmon (Salmo salar L.) fry (age 0+) distribution 1) shortly after the emergence and 2) after the assumed main dispersal period of fry. The effect of physical habitat variables (water depth, water velocity and substratum size), spatial spawning redd distribution and densities of older juveniles were examined using multiple linear regressions. Identical models were fitted with generalized habitat suitability indices to test their applicability to predict the variation in fry densities. Clear patterns of habitat use were found in relation to individual physical habitat variables and suitability indices, but there was a large variation in densities, with this variation often being largest within optimum habitats and the capability of regression models to explain this variation was relatively poor, ranging from 22 to 34 %. It is suggested that physical habitat variables may rather act as limiting edges than determinants of habitat selection of fry at within-reach scales. Fry densities were not significantly related to densities of older juveniles. Spatial spawning redd distribution was positively correlated with fry density approximately 2 months after the emergence. This result supports previous findings that the spatial distribution of spawning areas is an important factor that affects habitat selection of Atlantic salmon fry.

Syönnösvaellus ja nopea kasvu ovat olennainen osa Atlantin lohen (Salmo salar L.) ekologiaa, niinpä kasvunopeuden selvittäminen on tärkeä osa kalatutkimusta. Tuottavimmat syönnösalueet tulisi tietää, jotta olisi mahdollista suojella villejä sekä kalastaa istutettuja lohia kestävän käytön periaatteella. Tämän tutkimuksen tavoitteina oli selvittää Itämeressä elävän villin ja viljellyn Atlantin lohen kasvunopeuden eroja vuosien ja merialueiden välillä. Lisäksi pyrittiin selvittämään, vaikuttavatko saalislajien runsaus, saalislajisuhteet lohen ravinnossa ja veden lämpötila kasvunopeuteen. Absoluuttinen pituuskasvu arvioitiin takautuvalla kasvunmäärityksellä suomuista vuosilta 1989–2010. Suomut oli kerätty pääsyönnösalueilta (ICES osa-alueet (SDt) 25, 26, 28, 30 ja 32). Villin lohen ensimmäisen merivuoden kasvu oli nopeinta SD25:stä (pääallas) ja hitainta SD30:sta (Selkämeri) pyydetyillä yksilöillä, kun taas viljellyn lohen kasvu oli nopeinta SD32:sta (Suomenlahti) ja hitainta SD26:sta (pääallas) pyydetyillä yksilöillä. Villin lohen toisen merivuoden kasvu oli nopeinta SD28:sta (pääallas) ja hitainta SD30:sta pyydetyillä yksilöillä. Viljellyn lohen toisen merivuoden kasvu oli nopeinta SD25:stä ja hitainta Selkämereltä pyydetyillä yksilöillä. Villin lohen molempien merivuosien kasvunopeudessa oli nouseva trendi läpi tutkimusjakson ensimmäisen merivuoden kasvun ollessa viime vuosina keskimäärin 25 cm ja toisen merivuoden kasvun 30 cm vuodessa. Tutkimusjakson alussa viljellyn lohen ensimmäisen merivuoden kasvu oli noin 20 cm, mutta 1994 lähtien se on ollut 25 cm vuodessa. Viljellyn lohen toisen merivuoden kasvu oli tutkimusjakson alussa alle 15 cm, josta se on kohonnut lähes 30 cm:iin vuodessa. Villin lohen keskimääräinen kasvu oli nopeampaa molempien merivuosien aikana verrattuna viljeltyyn. Korkeamman lohen trofiatason ja suuremman kasvunopeuden välillä havaittiin yhteys ensimmäisen merivuoden aikana pääaltaalla, mikä viittaa saalislajisuhteiden vaikuttavan kasvunopeuteen. Lämpimämmän veden ja hitaamman ensimmäisen merivuoden aikaisen kasvun välillä havaittiin yhteys Suomenlahdella sekä lämpimämmän veden ja hitaamman toisen merivuoden aikaisen kasvun välillä pääaltaalla. Itämeren lohella vaikuttaa olevan alueiden ja vuosien välisiä eroja kasvunopeudessa. Tämän tutkimuksen perusteella ne näyttävät johtuvan lohen alkuperästä, ravinnonkäytöstä ja veden lämpötilasta. The feeding migration to the sea and the associated faster growth is an essential part of the ecology and life history of Atlantic salmon (Salmo salar L.). Thus the quantification of growth is an important part of fisheries research. The most productive feeding areas have a key role in the conservation of wild stocks and at the same time ensuring sustainable exploitation of reared stocks. The aims of this study were to investigate if there are spatial, temporal and stock (wild, reared) related differences in the growth of salmon in the Baltic Sea and to determine if individual diet preferences, prey species stock abundance and water temperature affect growth. The absolute length growth of Baltic salmon first and second sea growth season was back-calculated from time series (1989–2010) of archived salmon scales obtained from the main salmon feeding areas (ICES subdivisions (SDs) 25, 26, 28, 30 and 32). During first sea growth season wild salmon caught from SD25 (Main Basin) were fastest growing and individuals caught from SD30 (Bothnian Sea) grew slowest. Reared salmon caught from SD32 (Gulf of Finland) grew fastest during first sea growth season and individuals caught from SD26 (Main Basin) the slowest. During second sea growth season wild salmon caught from SD28 (Main Basin) were fastest growing and individuals caught from SD30 grew slowest. Reared salmon caught from SD25 had the fastest growth during second sea growth season and individuals caught from SD30 the slowest. There was a general increasing trend in the growth of wild salmon, recent growth during first sea growth season being annually 25 cm and during second sea growth season 30 cm. At the beginning of the study period reared salmon growth during first sea growth season was 20 cm, but since 1994 it has stayed close to 25 cm. Their growth during second sea growth season has been increasing through-out the study period from