Recent marine growth declines in wild and ranched Atlantic salmon <i>Salmo salar</i> from a western European catchment discovered using a 62-year time series

Abstract To address population declines, many salmon populations are supplemented with hatchery-bred fish. Little is known about how growth performance of and wild compare during critical periods such as the first summer at sea. This study compares scale measurements between 1725 ranched 1976 from Burrishoole catchment (western Ireland) over 62 years (1956–2017). Post-smolt (PSG) was greater in than fish; this difference consistent compensatory rather size-dependant growth. Temporal trends marine fish were similar, a marked decline PSG return size after early 2000s. The significantly related to freshwater autumn sea surface temperature Norwegian Sea. changes pattern intercirculi spacings along trajectory also identified; circuli deposited narrower 2000s 2010s compared earlier decades, while winter wider. recent affects both similarly, associated increasing manifested change well overall