Abiotiska faktorers inverkan på laxens (Salmo salar) dagliga lekvandring i två älvar i norra Sverige

Atlantic salmon (Salmo salar) depends on two major migrations to fulfil their life cycle, from their birth place in rivers to sea, and back upstream the river again to spawn. Salmon stocks have been heavily reduced during the last century due to human activities such as hydropower and timber floating. Construction of fish ladders and restoration of rivers are recent management actions taken aiming at improving the remaining salmon stocks. Salmon are monitored during their migrations to get information on the stock status. This study focused on how environmental factors correlated with adult salmon upstream spawning migration data from two rivers in northern Sweden, Västerbotten County, Umeälven and Byskeälven. Salmon data from both rivers were obtained from fish counters placed in fish ladders. The fish ladder in river Umeälven was equipped with two VAKI fish counters, and salmon data from 2010-2013 was used. Salmon data from 2009-2013 from river Byskeälven were used, the fish ladder was equipped with a PORO fish counter 2009-2012, and a VAKI fish counter 2013. There were three questions that led the study; (I) which environmental variables can explain the daily variations in salmon upstream migration? (II) Are there any major differences between the factors influencing salmon spawning migration in an exploited river compared to an unexploited river? (III) Can an environmental factor be of greater or less importance for salmon upstream migration during the first and the last half of the season? Stepwise linear regressions were used to create models to find how the environmental factors correlated with salmon upstream migration. Both rivers had a seasonal migration pattern with most of the salmon migrating early in the season. Water flow had most influence on the salmon upstream migration in the studied rivers. There was a difference in which environmental factors had most influence on salmon migration between the first and second 50 % of migrating salmon in river Byskeälven. Adjusted Julian day number explained most of the migration in the best model for the migration first half of the season. Water temperature, water flow, and adjusted Julian day number explained the migration in the second half of the season

Skillnader i migrationsframgång mellan vild och odlad laxsmolt (Salmo salar L.)

Laxen är en anadrom fiskart som reproducerar sig i sötvatten men lever huvuddelen av sitt vuxna liv i saltvatten. På grund av vattenkraftens dammbyggen hindras laxen att göra dessa habitatbyten och reproduktionen drabbas. För att kompensera för minskade laxstammar sätter vattenkraftbolagen varje år ut miljontals odlad laxsmolt i vattendrag som mynnar ut i östersjön. I Umeälven släpps 80000 laxsmolt ut årligen. Tidigare rapporter visar att överlevnaden hos dessa är lägre än hos vild smolt. I den här rapporten försöker vi ta reda på om det finns en skillnad i migrationsframgång mellan vild och odlad smolt i Umeälven och vad konditionsfaktorn har för betydelse för den odlade smoltens migrationsframgång. Vi har använt oss av tre grupper med fiskar, två odlade och en vild grupp. Dessa skiljer sig från varandra gällande storlek och konditionsfaktor. Vi har också genom akustiska sändare i samma individer mätt hur fort de migrerat och hur långt de har kommit. Överlevnaden varierade, vild smolt hade 39 % den odlade gruppen med lägre medelvikt hade 48 % och den odlade gruppen med högre medelvikt hade 16 % överlevnad till Holmsund. Migrationshastigheten varierade mellan sträckor i älven men inte mellan grupper av fisk. Tendenser fanns i alla grupper att smolten föredrog att migrera nattetid, tydligast var det bland de vilda smolten på den senare sträckan. Vi tycker att man i framtida kompensationsodlingar ska satsa på mindre smolt med lägre konditionsfaktor för att efterlikna vild smolt och därmed förhoppningsvis öka överlevnaden till havet.The Atlantic salmon (Salmo salar L.) is an anadromous fish. It reproduces in freshwater streams but spends the major parts of its mature life in seawater. Due to hydropower dams the salmon is prevented from making these habitat changes and reproduction is compromised. Hydropower companies stock millions of salmon smolt in the Baltic Sea annually to compensate for decreasing salmon populations. In the Ume River 80000 hatchery reared salmon smolts are stocked every year. Previous reports show that the survival of these smolts is lower than the survival of wild smolts. In this report, we try to find out if there is a difference in migration success between wild and reared smolts in the Ume River and how conditionfactor affect the migration success. We have used three groups of fishes, two hatchery reared groups and a wild group. These differ from one another regarding size and condition factor. Acoustic transmitters measured how fast they migrated and how far they came. The rate of survival was 39 % for the wild smolt, 16 % for the hatchery reared group with high condition factor and 48 % for the hatchery reared group with low condition factor. Migration rate differed significant between stretches of the river, but not among groups of fish. We also discovered that there was a tendency for all groups to migrate at night, especially among the wild smolts in the later stretch of the river. We think that future hatcheries should aim for smaller smolts with lower condition factor to mimic wild smolts and thus hopefully increase migration success