Lonely, but Strong; Management of the Remnants of a Historical Large-Grown Brown Trout Population

Conservation of natural systems are facing a new era with the implementation of next generation sequencing techniques allowing identification of adaptive traits and high resolution population structure. Lake Altevatn, North Norway, harbor one of the seven brown trout (Salmo trutta) populations defined as “large grown” in Norway. This population has experienced a drastic decline within the last decades and conservation actions have therefore been initiated by the nature managers. In the present study we used 19 microsatellites and 3135 informative SNPs to address whether large grown brown trout in L. Altevatn could be assigned to a single spawning location and to identify adaptive genetic traits. Additionally, we linked genotypic and phenotypic information to provide a synthesized advice for the continued conservation of the large grown brown trout. The results showed that 92 % of the brown trout characterized as large grown (> 474 mm) could be assigned to a single spawning creek. Moreover, we identified adaptive traits specific for the large grown brown trout from this spawning creek. Taken together with previous investigations, we conclude that the establishment of a supportive stocking program should be avoided, since the consequences for the native large grown brown trout population are unpredictable.