Anadromous alewives (Alsoa pseudoharengus) and blueback herring (A. aestivalis) are sympatric from New Brunswick and Nova Scotia to upper South Carolina. Alewives range allopatrically north to Labrador and Newfoundland, while blueback herring are found south to Flotida. The two species are collectively referred to as alewife, gaspereau, or river herring because of similarities in appearance, time of spawning, methods of capture, and uses of the commercial catches. Despite their similarities, there are important life history differences. Alewives select lentic areas for spawning. Blueback herring spawn in lotic sites in the sympatric distribution, but primarily use lentic sites in their allopatric range. The differential selection of spawning sites by blueback herring reduces competition with alewives for spawning grounds in sympatry. River herring return to natal streams for spawning, but they also readily colonize new streams or ponds and reoccupy systems from which they had been extirpated. Negative phototropic behavior is exhibited by juvenile river herring in the nursery areas and by adults in the coastal waters. Alewives remain deeper in the water column than blueback herring in both locations. The vertical separation, and the choice of different spawning sites by adults, could reduce interspecific feeding competition between juveniles of the two species. The phototropic behavior can effect estimates of species composition, relative abundance, and feeding chronology and intensity. All life stages of both landlocked and anadromous river herring provide forage for many freshwater and marine predators. The mortality of anadromous alewives provides an important source of nutrients for headwater ponds.