Predation by northern pike Esox lucius on migrating hatchery-reared salmonid smolts
(English)Manuscript (preprint) (Other academic)
Supplementary stocking of hatchery-reared smolts is the main method used to mitigate and compensate for lost production of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) populations in rivers. The survival of hatchery reared smolts in nature is generally low, and predation is one explanation for this. In the River Klarälven, Sweden, approximately 175 000 hatchery reared salmon and trout smolts are annually released into the rivr approximately 25 km upstream of Lake Vänern, to where they migrate and remain until maturity. During 2006-2010 half of the released hatchery reared smolts tagged with telemetry transmitters did not reach Lake Vänern. The loss rate of smolts was higher in river reaches with shallow vegetated areas and in reaches with deep pool areas than in the dominant habitat type, consisting of intermediate depths and sandy, uniform bottom substrates. Similarly, average CPUE of northern pike (Esox Lucius) was high in the same habitats as where smolts were lost. Gut content analyses of pike showed that they fed chiefly on European smelt (Osmerus eperlanus) in April, hatchery-reared salmonid smolts in May and European river lamprey (Lampetra fluviatilis) in June. We argue that when these different energy and lipid rich alternative prey occur at high densities during their spawning periods they are probably an easily caught energetically favorable prey. Our results indicate that there may be ecological windows of opportunity for stocking hatchery-reared smolts that could increase survival in the River Klarälven.
ecological window; habitat-specific predation; migration; opportunistic predator; salmonid management
Research subject Biology
IdentifiersURN: urn:nbn:se:kau:diva-31979OAI: oai:DiVA.org:kau-31979DiVA: diva2:714120