Aquaculture and the conservation of wild salmon populations

Abstract

Aquaculture of Atlantic salmon is a highly successful industry that affects wild salmon populations in ways that threaten their genetic integrity and viability. We have identified a set of SNPs that distinguish between wild and farmed salmon, and developed a statistical method to quantify genetic introgression of escaped farmed to wild salmon. One half of 200 studied wild populations in Norway show significant introgression of farmed salmon in wild salmon (1). The level of introgression increases significantly with the proportion of escaped farmed salmon in the population over the last 25 years. Introgression affects several vital life-history traits of wild salmon. The age and body size at return of wild salmon to a river vary with the level of introgression, and differ between groups of populations having different phylogenetic origin and ecotype (2). Controlled experiments of families of wild and farmed salmon, and their hybrids, show differential survival between wild and farmed offspring in nature. Moreover, the experiments have uncovered some of the mechanisms that determine the fitness and effects of farmed offspring in the environment. Our study and an extensive literature (3) provide evidence that domesticated introgression has a strong effect on important biological characteristics of wild populations. We expect gene flow from other genetically altered domesticated animals to have similar effects on their wild conspecifics. The methodology used in these studies can serve as a model for how to quantify and understand effects on wild biodiversity of domesticating aquatic organisms.

(1) Karlsson, S., Diserud, O. H., Fiske, P. & Hindar, K. 2016. Widespread genetic introgression of escaped farmed Atlantic salmon in wild salmon populations. ICES Journal of Marine Science 73: 2488–2498. doi:10.1093/icesjms/fsw121

(2) Bolstad, G.H., Hindar, K., Robertsen, G., Jonsson, B., Sægrov, H., Diserud, O.H., Fiske, P., Jensen, A.J., Urdal, K., Næsje, T.F., Barlaup, B.T., Florø-Larsen, B., Lo, H., Niemelä, E. & Karlsson, S. 2017. Gene flow from domesticated escapes alters the life history of wild Atlantic salmon. Nature Ecology & Evolution, 1: 0124. DOI: 10.1038/s41559-017-0124

(3) Glover, K.A., Solberg, M.F., McGinnity, P., Hindar, K., Verspoor, E., Coulson, M.W., Hansen, M.M., Araki, H., Skaala, Ø. & Svåsand, T. 2017. Wild Atlantic salmon, farmed escapees and genetic interactions: status of knowledge and unanswered questions after 40 years of research. Fish and Fisheries, 18: 890-927. DOI: 10.1111/faf.12214.