Variability in the Abundance of Fish Stocks on the Continental Shelf of the Northwest Atlantic Ocean

Research vessel survey data has provided indices of relative abundance of at least fifty species of fish on the Continental Shelf of the Northwest Atlantic for the past forty years.  Many species have declined in relative abundance, while others have increased.  The decreases and increases are generally not monotonic.  Rather, the increases and decreases of some stocks reflect a two or threefold change in relatively few years.  Many of the changes occurred during the mid 1980s and early 1990s, depending on location.  Some of the changes are correlated among species.  Most of the correlations are positive, indicating a bottom-up control.  Causal factors are considered, particularly with respect to the population dynamics of associated zooplankton.