Cooperative Fish and Wildlife Research Units Program: Maine
Education, Research and Technical Assistance for Managing Our Natural Resources

Since the early 20th century, passage by American shad past Veazie Dam (rkm 48) was biologically trivial. Spawning habitat for the population was restricted to the tidal estuary. Dam removals (Veazie and Great Works; rkm 60), and upstream fish passage modifications at other dams, are anticipated to reconnect American shad to most of their historic freshwater habitat upstream of Milford Dam (rkm 62). To assess how this change in access may influence estuarine use, we sampled both adult and juvenile shad. Adults were sampled in 2013-7 (cohorts restricted to the estuary; n= 540). Juveniles (n=220) were collected from the estuary (April to September), from 2011-4 (restricted to the estuary) and 2015-7 (connected to freshwater habitat). Otoliths were taken from all fish for age analysis; scales from adults were taken to assess spawning history. Adults were dominated by older age classes (4–8 yr) with a high incidence of repeat spawning. Otolith microchemistry (Sr and Ba) suggests that many juveniles were reared in elevated salinities, often moving into freshwater prior to fall migration. The general pattern of salinity use by juveniles has remained qualitatively unchanged post dam removal, likely reflective of low upstream recruitment.