Genetisk analys av avelsfisk, Lax och havsöring 2017-2018 från svenska kompensationsodlingar

Hatchery reared salmon and sea trout are released in several of Sweden's major rivers, as compensation for reduced natural reproduction due to hydropower exploitation. To separate hatchery fish from wild conspecifics, all farmed fish released must have their adipose fin removed. In addition, according to water court decisions, a small amount of the released fish must be individually tagged. For many years, external tags (i.e. Carlin-tags) were used for large-scale tagging of smolts. However, for several reasons the reporting rates of recaptured tags in the Baltic Sea have declined significantly, and therefore it has been a reduction in the use of the Carlin-tags. As an alternative to external tags, one can utilise the fact that all individuals are "genetically labeled" from birth by individually unique DNA-profiles. Collection of DNA-samples from spawners allows for various follow-ups of breeding activities such as identification of full-siblings among spawners and of strayers from other rivers. Over time, it is also possible to assign parents to returning offspring. In this report we presents results following DNA analysis of salmon and sea trout spawners from six and five compensatory hatcheries in Sweden, respectively. The aim has been to lay the foundations for a "genetic labeling program" for these species. All hatchery stocks showed comparatively high levels of genetic variation, which can be explained by the fact that new spawners are collected each year (i.e. sea ranching) and that straying between rivers occurs (i.e. some fish migrate to another river than where it was born). Brood stocks in 2017 and 2018 mainly consisted of “homers” although some strayers could be identified. Genetic similarity was higher between years within rivers than it was between rivers. Generally, hatchery stocks in neighboring rivers were also genetically more similar to each other – a pattern seen in wild salmon and sea trout. However, sea trout from northern Lule River deviated by being were genetically most similar to sea trout from the distant southern rivers Dalälven and Ljusnan. These similarities could reflect earlier transfers of fish (genetic material) between hatcheries. A number of full-sibling groups of varying sizes were identified among the analysed spawners, and in some cases full-sibs had also been artificially fertilised. The hatchery at River Skellefteälven have had their brood-stock genetically analysed for several years; for the fish stripped in 2018 it was possible to identify parents (from 2014) to 89 % of the returning spawners.