The hatchlings known as, the Young of Year (YOY), eat voraciously as they grow and get ready for their trip downstream in the late summer/early fall.  They eat plankton. Plankton eat algae. Algae eat the phosphorus that is introduced into the lake mostly through farm run off, and septic leakage. Phosphorus causes the algae bloom so common on lakes.  A healthy alewife population will then swim out of the lake with a large portion of the phosphorus on board possibly eliminating the need for drawdowns. Drawing down a lake is expensive and disruptive to the ecosystems in the lake and surrounding wetlands. If  opening up the watershed for alewife migration allows for natural flushing of the phosphorus  then we humans have found another way to live working with nature and save money at the same time.

The alewives have access to spawning grounds they have not seen in 300 years. When this began alewives had disappeared from 90% of their range from Atlantic Canada to Georgia. As a keystone species they left a big hole at the bottom of the food chain.  Every female alewife lays 100,000 eggs. X % get eaten by other fish. The rest hatch, eat plankton and in the early fall start downstream. On the way x % die. The rest travel to the ocean where they meet the big fish, the very big fish and seals and birds and whoever might want to eat them. X % survive for four years until it is time to return to the rivers. The large mouth bass in the lakes get bigger. Fishermen love it. The lower Sebasticook has the largest number of eagles in one place on the East Coast. During this time the alewives fed salmon, groundfish, eagles, osprey, seabirds, and mammals providing clean eating for river fish and birds coming in from the ocean. the YOY  ate down the plankton load in the lakes by half. So during this time this small fish has fed and enriched an entire biome, more fish in the river, more birds above, more mammals.

As they head back in four years to the mouths of rivers from the open ocean they draw in the fish who have gotten wise to their itinerary. We are talking Cod. We love to talk Cod.  Historically cod have gone to the mouths of the rivers in huge numbers to eat spawning alewives. We know the Cod numbers in the Gulf of Maine are way down. If the river herring provides  food for cod will their numbers rebound? We don’t know but if history bears out and warming ocean waters do not intervene, then maybe.  Cleaner lakes, more forage, and more fish. Someday as the rivers get cleaner, salmon will run with the alewives. The large numbers of alewives provide cover for commercial fish like eels and salmon. A bonus from this remarkable fish.