There are several species of anadromous and catadromous fish, including brook trout, winter flounder, blueback herring, alewife, rainbow trout, large brown trout, American shad ("Alosa sapidissima"), hickory shad, smallmouth bass, Atlantic sturgeon, striped bass ("Morone saxatilis"), American eel, sea lamprey, and endangered shortnose sturgeon and dwarf wedgemussels. Additionally, the United States Fish and Wildlife Service has repopulated the river with another species of migratory fish, the Atlantic salmon, which for more than 200 years had been extinct from the river due to damming. Several fish ladders and fish elevators have been built to allow fish to resume their natural migration upriver each spring.