Populations on the Brink: Low Abundance of Southern Upland Atlantic Salmon in Nova Scotia, Canada

Populations of Atlantic salmon Salmo salar in the Southern Upland region of Nova Scotia, Canada, have declined to very low abundances. Sixty‐three rivers in this region—9% of the total number of Canadian rivers that contain Atlantic salmon—are known to have supported populations in the recent past. Annual adult abundance data from four rivers show declines of 83–99% from peak levels in the 1980s; this pattern is consistent with trends in recreational catch within the region. Regionwide comparisons of juvenile density data from more than 50 other rivers indicate significant ongoing declines and provide evidence for river‐specific extirpations. Based on surveys conducted in 2000 and again in 2008–2009, total juvenile density decreased substantially at the majority of locations; during the 2008–2009 survey, juveniles were not found at nine sites (four rivers) where they were present in 2000. Although river acidification has significantly contributed to the deterioration or extirpation of Atlantic salmon populations from many Southern Upland rivers during the last century, contemporary declines occurring in nonacidified rivers indicate that other factors are now affecting these populations. Several lines of evidence demonstrate that Southern Upland Atlantic salmon are biologically unique and that their extinction would constitute an irreplaceable loss of Atlantic salmon biodiversity. Received November 2, 2010; accepted June 2, 2011