Marissa McMahan

Director of Fisheries

Restoration of river herring is critical to rebuilding coastal ecosystems and strengthening climate resilience as the Gulf of Maine continues to warm. Manomet supports community-driven river herring restoration and is tracking the impact of such efforts on river herring abundance and coastal food webs. 


River herring is a collective term for two species, alewives and blueback herring. They are anadromous, which means they live primarily in the ocean and migrate upstream each spring to spawn in freshwater lakes and ponds before returning to the ocean. Historically, they have been foundational species in the Gulf of Maine ecosystem, comprising an important source of forage, along with marine species such as Atlantic herring and menhaden, for birds, mammals, and commercially valuable species including cod and haddock. Over the last four hundred years, dams, offshore trawling, and pollution have reduced river herring populations to a small fraction of their historic levels. However, the passage of the Clean Water Act, removal of many dams and installation of fishways in many more, and limits on harvesting have jumpstarted the renewal of river herring populations in the Gulf of Maine. 


The spring migration, when hundreds of thousands of fish surge upstream to reach their spawning grounds, is a natural phenomenon that draws predators, such as osprey and bald eagles, fishers who harvest the fish for bait, and nature lovers enjoying a spectacle of spring renewal. But much of the ecological impact of river herring restoration comes when juvenile river herring leave their natal lakes and ponds and head to the ocean in the fall – by the trillions.  


Research is underway on many fronts to measure the impact of river herring restoration coastal food webs. Manomet’s contributions include testing the application of high-resolution sonar and environmental DNA to measure outmigration of juveniles which are difficult to sample with more traditional methods. In addition, we are tracking research conducted by others, including analysis of groundfish stomach contents and the use of stable isotopes to track nutrients derived from river herring juveniles through marine food webs.