Marine Ecosystem Conditions Affect North American Atlantic Salmon Populations

North American Atlantic salmon (Salmo salar) populations experienced substantial declines in the late 1980s and early 1990s, and many populations have persisted at low abundances.  The coherence of declines among populations from Maine to Quebec suggests a shift in marine survivorship, rather than the influence of river-specific factors.  While the processes controlling marine survival of Atlantic salmon are poorly understood, concurrent physical and biological shifts in the Northwest Atlantic ecosystem have been documented.  We use time series analyses to identify and quantify the influence of climate, oceanographic, and low trophic level conditions on Atlantic salmon during their marine migration, overwintering, and feeding stages.  Findings indicate that a cascade of climate-driven events in the Northwest Atlantic affected sea surface temperature, primary production, zooplankton, and ultimately Atlantic salmon.  The strongest relationships point towards important effects while salmon are overwintering in the Labrador Sea and feeding near Greenland.  In addition, the relationships between Atlantic salmon abundance and Northwest Atlantic ecosystem conditions shift over time, and salmon populations now may be controlled by different ecosystem factors than they were prior to major population declines.