Effect of Environmental Conditions on River Herring Freshwater Survival: A Coastwide Perspective

River herring, alewife (Alosa pseudoharengus) and blueback (Alosa aestivalis), have declined throughout their range, and the National Marine Fisheries Service has determined river herring to be a species of concern. Because of their diadromous life-cycle freshwater stressors can affect their recruitment. We analyzed juvenile and spawner abundance for four alewife and blueback herring stocks along the northeast shelf of the United States. GAM models were employed to compute empirical relationships between river herring freshwater survival and environmental conditions. Variation in temperature or river flow during three critical periods, early spring, late spring or late summer, drove a substantial fraction of the observed variability in survival. However, there existed system specific differences in the shape of the environment-survival relationship, the specific month that imparted this environmental effect, as well as the best combination of environmental effects accounting for most of the variation in survival. River specific factors, such as the number of predators or habitat characteristics, as well as latitudinal gradients in environmental conditions, may have resulted in the existence of different “survival-limiting” temporal windows and environment-survival relationships in each river. Notably, late spring temperature had an opposite effect on survival in the southernmost river than in more northern systems.