Interaction between hatchery and wild juvenile white‐spotted charr Salvelinus leucomaenis in a stream enclosure experiment

Abstract

The competitive interactions between hatchery and wild juvenile white‐spotted charr Salvelinus leucomaenis were examined in enclosure experiments in a natural stream. A total of 24 enclosures (1·0 × 1·0 × 0·7 m height) were arranged in stream in an array for randomized block design with replicates of three treatments (wild fish only, hatchery fish only, wild plus hatchery fish). Three experiments were conducted in 2006, using different densities and sizes for each experimental trial. When densities in enclosures were controlled to be equal among treatments (4 individuals m−2: substitutive design), wild fish in the presence of hatchery fish had significantly higher growth rates than the wild fish alone treatment. When densities in enclosures were controlled to be 4 individuals m−2 hatchery fish only treatment, 4 individuals m−2 wild fish only treatment and 8 individuals m−2 in the hatchery plus wild fish treatment (additive design), wild fish in the presence of hatchery fish had significantly lower growth rate than the wild fish alone treatment. Hatchery fish in the presence of wild fish also grew significantly slower than the hatchery fish alone treatment. When densities in enclosures were controlled to be equal among treatments (4 individuals m−2) but hatchery fish were 1·1 times longer than wild fish, growth of wild fish in the presence of the larger hatchery fish did not differ significantly from growth of the wild fish alone treatment. These results suggested that relative size of hatchery fish in relation to wild fish and increased fish density are two important factors influencing the growth of wild juvenile S. leucomaenis.