Research Document - 2013/005
Recovery Potential Assessment for Southern Upland Atlantic Salmon: Status, Past and Present Abundance, Life History and Trends
By H.D. Bowlby, A.J.F. Gibson, and A. Levy
Abstract
The purpose of this research document is to provide background information on the present status and recent trends of Atlantic salmon populations in the Southern Upland region of Nova Scotia in support of recovery planning for this designatable unit. Information related to abundance, trends, and recovery targets is provided.
The available data indicate that the abundances of Southern Upland Atlantic salmon populations are low and declining. Annual adult abundance data from four rivers show declines of 88% to 99% from maximum abundance, a pattern consistent with trends in the recreational catch in the region. Region-wide comparisons of juvenile density data from more than 50 rivers indicate significant ongoing declines and provide evidence for river-specific extirpations. Comparing juvenile densities at locations surveyed in 2000 and again in 2008/09, total juvenile density decreased substantially in the majority of locations and juvenile Atlantic salmon were not found at nine sites and in four rivers where they had been found in 2000. Although river acidification has significantly contributed to the deterioration or extirpation of populations from many rivers in the region during the last century, contemporary declines in non-acidified rivers indicate that other factors are impacting populations.
Recommended recovery targets for Atlantic salmon populations in the Southern Upland have both abundance and distribution components. The conservation requirements based on the amount of habitat area and an egg deposition rate of 2.4 eggs/m² are proposed as river-specific abundance targets, until the dynamics of recovered populations can be studied. Distribution targets should encompass the range of variability among populations, here described genetically and with river-specific environmental characteristics. There is the expectation that including a wider variety of populations in the distribution target will enhance short-term persistence, as well as facilitate recovery in the long term. Recovery targets will need to be revisited as information about the dynamics of the recovering population becomes available.
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