For many years, the thousands of miles that migratory fish traveled every year along the St. Croix River were filled with obstacles.
Dams cut off ancient routes connecting rivers, lakes, and oceans for centuries. Many species were unable to make their way to the areas they once spawned in.
The engineers’ proposed solution seemed deceptively easy: build improved passageways for fish around the dams. The project would be aimed toward fish like American eel, American shad, and alewives.
However, the story did not end there with the fish.
Something interesting happened much farther away from where the fish swam.
Six hundred miles reopened
The Woodland Dam is located on the St. Croix River in Eastern Maine. Officials identified it as a key barrier to migratory fish.
The dam has an old fishway built in the 1960s.
Officials deemed the current fishway insufficient for today’s restoration goals.
In addition to the fish lift and passage improvements, the project called for restoration of flow throughout the watershed. This would allow the full range of migratory species to return to their historical spawning grounds.
Those species included American eels, American shad, alewives, and blueback herring.
The scope of this project is significant.
Restoration efforts have the potential to open up approximately 600 miles of spawning area. Additionally, the project will restore about 60,000 acres of spawning habitat for alewives.
On paper, it appears as though the project is centered around fish.
However, the truth is that it is initiating larger environmental changes.
The fish that feeds everything else
There is one species at the heart of these restoration efforts: the alewife. Alewives are often referred to as “the fish that feeds all.”
This refers to the fact that they are a keystone species within the food web.
Predators of alewives include eagles, seals, cod, haddock, and numerous other marine animals.
Whales are among those marine animals.
Every spring, alewives migrate from the ocean into freshwater and back again to spawn. Their migration creates a connection between freshwater and marine ecosystems.
Alewife migrations transfer energy throughout the regional food web.
When alewife populations decline, predator populations often decline as well. Conversely, when alewife populations increase, those benefits can spread across large geographic ranges.
The Fish and Wildlife Service notes that restoring fish passage could reconnect hundreds of miles of habitat for migratory species.
According to NOAA Fisheries, restoration efforts may lead to supporting North America’s largest alewife run.
If restoration efforts are successful, tens of millions of spawning alewives may inhabit the watershed. That possibility extends well beyond just the river system itself.
What the restoration was really rebuilding
Fish passage was clearly the main impediment that prevented habitats created by dams from being restored. A new fish lift was created to help solve that problem.
Yet as we know, ecological recovery does not typically occur in isolation.
Fish population recoveries are helping reveal those connections.
What happened when the whales appeared?
The whale sightings dramatically altered how people perceived the project. They demonstrated that this restoration project was having effects beyond allowing fish to swim upstream past dams.
Alewives act as a bridge between rivers and oceans.
When alewife populations begin to grow and thrive, it provides predators with a greater food base.
Whales were an icon for the recovery of a long and complex food web. However, its potential impact could reach hundreds of miles through interconnected systems.
It eventually revealed how ecosystems depend upon connections that often go unnoticed. The returning whales suggested those connections reached far beyond the river itself.
Researchers are now beginning to see whether similar recoveries could reshape food webs in other restored river systems.
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