Captive-bred Atlantic salmon released into the wild have fewer offspring than wild-bred fish and decrease population productivity

• Published in: Proceedings of the Royal Society B: Biological Sciences
• Main Authors: O'Sullivan, Ronan James, Aykanat, Tutku, Johnston, Susan E., Rogan, Ger, Poole, Russell, Prodöhl, Paulo A., de Eyto, Elvira, Primmer, Craig R., McGinnity, Philip, Reed, Thomas Eric
• Other Authors: Suomen Akatemia, Science Foundation Ireland, Marine Institute, H2020 European Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2020
• Subjects: Atlantic salmon
• Online Access: http://dx.doi.org/10.1098/rspb.2020.1671; https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2020.1671; https://royalsocietypublishing.org/doi/full-xml/10.1098/rspb.2020.1671

The release of captive-bred animals into the wild is commonly practised to restore or supplement wild populations but comes with a suite of ecological and genetic consequences. Vast numbers of hatchery-reared fish are released annually, ostensibly to restore/enhance wild populations or provide greater angling returns. While previous studies have shown that captive-bred fish perform poorly in the wild relative to wild-bred conspecifics, few have measured individual lifetime reproductive success (LRS) and how this affects population productivity. Here, we analyse data on Atlantic salmon from an intensely studied catchment into which varying numbers of captive-bred fish have escaped/been released and potentially bred over several decades. Using a molecular pedigree, we demonstrate that, on average, the LRS of captive-bred individuals was only 36% that of wild-bred individuals. A significant LRS difference remained after excluding individuals that left no surviving offspring, some of which might have simply failed to spawn, consistent with transgenerational effects on offspring survival. The annual productivity of the mixed population (wild-bred plus captive-bred) was lower in years where captive-bred fish comprised a greater fraction of potential spawners. These results bolster previous empirical and theoretical findings that intentional stocking, or non-intentional escapees, threaten, rather than enhance, recipient natural populations.