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Interconnected Ecosystem - Aquatic Resources

Rainbow smelt.  Credit: NOAA

Increased access or water quality improvements in the GOM watersheds will benefit Atlantic salmon and many other native fish species, including:  Atlantic and shortnose sturgeon, alewives, blueback herring, American shad, sea lamprey, rainbow smelt and American eel.

By restoring natural stream processes, the overall ecological function of a watershed improves significantly.  The removal of dams allows many of these species to move freely between the larger mainstem river habitat into the smaller tributaries to access habitat for spawning and rearing of juveniles.

In time, as more rivers and streams become free flowing or accessible to diadromous fish, the watershed returns to a more natural state.  These collective changes add up, creating a ripple effect that vastly improves the overall health of the broader ecosystem, affecting a greater variety of species, either directly or indirectly.

Sea lamprey.  Photo credit: NOAA
Habitat Improvements: The sea lamprey influences aquatic habitat in Maine’s rivers and streams.  In constructing spawning nests, sea lampreys deposit stones in loose piles, which act to remove silt from stones already on the river bottom, which makes the substrate ideal for spawning Atlantic salmon.  In addition to creating an attractive spawning area, silt-cleaning activities may improve the “quality” of the immediate aquatic environment with respect to aquatic organisms, such as increasing insect diversity and abundance.

Nutrient Cycle: Diadromous species cycle nutrients between the marine & freshwater environments.  At sea, adults exploit the ocean’s rich food sources.  When they return to spawn in freshwater, they bring with them “marine-derived” nutrients that have been converted into growth.  These nutrients are released into freshwater ecosystems during and after spawning in the form of eggs and as carcasses of adults that have died.

Alewife.  Photo credit: Jerry Prezioso, NOAA


Prey Buffer: Diadromous species provide critical foodweb links under-pinning a healthy ecosystem.  In addition to providing food for many aquatic and terrestrial creatures, other species may decrease predation pressure on Atlantic salmon by providing additional food (i.e., “prey buffer”) for native predators.  For example, adult alewives and rainbow smelt migrate upriver to spawn at the same time Atlantic salmon smolts migrate to sea.  With greater numbers and a similar body size, these fish can provide cover from predators like, smallmouth bass, pickerel and striped bass which might otherwise prey upon Atlantic salmon smolts.  Juvenile river herring and shad, buffer young Atlantic salmon from relentless avian predators such as mergansers, great blue herons, eagles, osprey and double-crested cormorants.  Likewise, in the marine environment, anadromous fish provide a nutrient rich prey source for nearshore predators such as cod, haddock, pollock, harbor seals and grey seals, and offshore predators such as dolphins and porpoises.