Survival, growth and hatching of brown trout Salmo trutta embryos were studied using in situ incubation experiments in two lake outlet streams in Finland. The experimental design in both streams included an outlet site and a reference site far downstream. The date of hatching was recorded and the Elliott–Hurley model was then used to predict the time of emergence based on water temperature. For data analyses, the incubation period was divided into ‘winter’ (from fertilization to mid March) and ‘spring’ (from mid March until the end of the experiment). Temperature of the large-lake outlet remained at 1° C through the winter, while in other sites temperature was close to 0° C. In spring, temperature increased more slowly in the large-lake outlet. The survival of embryos was overall very high, from 83 to 98%, and they were larger in the outlets than in the downstream sites. Embryos hatched at the large-lake outlet in March, and 3–5 weeks later in the other sites. Although there were considerable between-site differences in hatching intervals, difference in expected 50% emergence dates of the earliest and latest site was only 4 days. Thus, any growth advantage that the outlet embryos had in winter disappeared by the end of the alevin period. Lake outlets, however, may be important for age 0 year brown trout later during the summer when other stream habitats do not provide adequate food resources.
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Document Type: Regular Paper
Department of Biological and Environmental Science, University of Jyväskylä, P. O. Box 35, 40014 University of Jyväskylä, Finland
Central Finland Regional Environmental Centre, P. O. Box 110, 40101 Jyväskylä, Finland
Publication date: 01 March 2008