Jan. 14, 2013 Salmon runs are notoriously variable: strong one
year, and weak the next. New research shows that the same may be
true from one century to the next. Scientists in the past 20
years have recognized that salmon stocks vary not only year to
year, but also on decades-long time cycles. One example is the
30-year to 80-year booms and busts in salmon runs in Alaska and
on the West Coast driven by the climate pattern known as the
Pacific Decadal Oscillation. Now work led by University of
Washington researchers reveals those decadal cycles may overlay
even more important, centuries-long conditions, or regimes, that
influence fish productivity. Cycles lasting up to 200 years were
found while examining 500-year records of salmon abundance in
Southwest Alaska. Natural variations in the abundance of
spawning salmon are as large those due to human harvest. "We've
been able to reconstruct what salmon runs looked like before the
start of commercial fishing. But rather than finding a flat
baseline -- some sort o