| Summary: | Hagen, I.J. & Karlsson, S. 2023. Knowledge gained from evaluating 16 Norwegian stocking programs for Atlantic salmon (Salmo salar). NINA Report 2347. Norwegian Institute for Nature Research. The Norwegian Institute for Nature Research (NINA) and collaborators have evaluated the effects of stocking in 16 supplementation programs for Atlantic salmon in Norway. Of these, eight release eyed eggs or alevins, four release smolts and four release smolts as well as earlier life history stages such as parr, eyed eggs and alevins. Using molecular genetic methods, we have analyzed a total of 67 cohorts in the 16 stocking programs and genotyped around 6000 individuals in addition to the broodfish. For 39 cohorts the data was suitable to estimate the effective number of broodfish. The outcomes of these studies indicate: 1. Norwegian stocking programs typically use around 20 – 30 broodfish each brood year. 2. In 20 of the analyzed cohorts, a Ryman-Laikre effect was observed and in 17 of these cohorts, the effect was substantial. This means that the number of broodfish used has not been balanced against the proportion stocked fish and the number of wild breeders in the population. Particularly when smolts have been released, the proportion stocked fish has been too large considering the number wild spawners and the effective number of broodfish. 3. A severe Ryman-Laikre effect - as observed in some of the stocking programs - is expected to lead to reduced genetic variation over time, thus compromising the population’s ability to adapt to environmental changes. In three stocking programs with severe Ryman-Laikre effect, the data allowed temporal comparisons and showed that the effective population size indeed had been reduced over time. 4. In stocking programs releasing smolts, the proportion stocked fish for 15 out of 21 analyzed cohorts was over 40% (found in five stocking programs) and around 80% (found in three stocking programs) for five of these cohorts. 5. Out of nine stocking programs where the size of the broodfish ...
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