Temporal trends in Atlantic salmon parr densities in northeast U.S. rivers

Atlantic salmon populations in the United States have declined dramatically and persistence is heavily dependent upon stocking juvenile fish, predominantly fry. The success of stocking hatchery fry is evaluated annually throughout New England by electrofishing surveys targeting age 1 parr. The objective of this study was to examine temporal trends in parr densities throughout New England and determine if trends vary among river basins.  We fit generalized additive mixed models to investigate potential linear and nonlinear temporal trends in parr density.  Akaike’s Information Criterion was used to evaluate competing hypotheses about how temporal trends vary regionally. The top-ranked model suggested two groups of rivers. The first group, (the Penobscot River) showed a nonlinear trend where parr densities increased until the 1990’s and then rapidly decreased to the present time. The second group (all other rivers) showed a linear decrease throughout the time series. These parr density trends reflected similar trends in spawning escapement for both groups of rivers. It appears that fry stocking has not been able to overcome the decrease in spawning escapement and altered stream ecosystems in New England and additional management strategies should be considered.