A single river may see only a few individuals, while others may have thousands of migratory fish per year. From the earliest times, pre-Colonial days into the 20th century, river herring, sturgeon and eels have been considered an important food source, often eagerly awaited after harsh winters. Alewife and blueback herring River herring are actually two distinct species, the alewife and the blueback, but the two are so closely related as to be almost indistinguishable. So, the common name river herring is generally used for both. River herring are anadromous, meaning that they feed in saltwater most of their life, but return to freshwater to reproduce. They are found along the entire East Coast, ranging from Nova Scotia to the St. Johns River in northern Florida and migrating up and down the coast with the change of seasons.