The Problem: Dams and industrial practices have blocked spawning habitat and decimated migratory fish populations. Flows at main stem hydro-electric dams and canals, as well as industrial pollution and heated plant discharges into the river make this situation worse. Determined action is needed if the Connecticut’s fish runs are to survive.

The Solution: require safe and effective fish passage at all main stem dams. Discontinue any recent industrial practices that may be injuring migratory fish runs. Undertake adequate testing before making changes to main stem discharges and flow regimes to prove they will do no harm. Continue to remove or create passage at tributary dams to increase available spawning habitat and success.

All fish are mobile, but none on the Connecticut River make longer journeys than the suite of migratory fish moving upriver from the Atlantic Ocean: blueback herring, alewives, American shad, American eels, Atlantic salmon and sea lampreys. These migrations have been taking place for thousands of years. The journeys of these species may take them through thousands of ocean miles annually, and nearly 200 miles upriver.

  • Anadromous fish: Shad, lamprey, salmon, blueback herring and alewives are anadromous fish. They are born in freshwater, swim to the sea to feed and mature, then return to the rivers of their birth to spawn. Though some members of each species die after spawning, only the sea lamprey spawns as the final act in its long life cycle. All other species may survive, return to the ocean and then return to the river to spawn again.
  • Catadromous fish: The American eel is a different fish. It is a catadromous species, growing and maturing in rivers and estuaries then returning to spawn in the ocean, then die. After years feeding and maturing in river and estuaries throughout the watershed, American eels head to the Sargasso Sea, a weed-covered expanse in the Caribbean, where they mate along that sprawling sargassum algae mat in close proximity to their counterparts, European eels. This seaweed expanse has also been found to be the protective ocean habitat that young loggerhead sea turtles journey to after hatching on sandy shores and skittering into the sea.

Main stem and tributary dams are among the major, human-induced contributors to declining migratory fish populations on the Connecticut River. Fish passage facilities are in place at most main stem dams. But changes in operations and discharges at main stem sites, as well as failing fish passage facilities, are further impacting surviving fish runs. In addition, thousands of poorly designed road crossings block fish from reaching available habitat. Culverts at these locations need to be replaced with  fish-friendly structures.

Critical fish passage and dam-removal work is also taking place on many tributaries and is in the works for others. We have successfully helped create fish passage, restore habitat and remove unneeded dams at dozens of watershed sites. In doing so we’ve opened up nearly 50 miles of migratory fish habitat.

The once prolific runs of American shad, blueback herring, alewives and Atlantic salmon have been dramatically reduced over the centuries. Today, runs are a small fraction of their historic numbers. These species play an important role in a healthy river and marine ecosystem.


Shortnose sturgeon are the only federally endangered migratory fish on the Connecticut River. They evolved in the age of the dinosaurs and are toothless and primitive looking—with bony plates instead of fish scales. Shortnose sturgeon are between 2 – 4 feet long and weigh up to 14 lbs. They mature slowly and don’t spawn until they reach 8 – 12 years old. Federal fines up to $20,000 can be levied for harming a shortnose sturgeon. The total river population is estimated at 1,200 fish.

Shortnose sturgeon live in the Connecticut River from below Turners Falls dam to the estuary at Long Island Sound. They typically migrate from salt water into rivers to spawn. However, main stem dams impede this species’ movements on the Connecticut River and there are now two distinct populations on the river–one is partially landlocked above the Holyoke dam. Unfortunately, only the population living above Holyoke dam is known to spawn successfully.

American eels enter the Connecticut River as tiny, transparent, glass eels. They are born in the Sargasso Sea, then migrate to rivers and estuaries to mature. American eels will spend from 8 – 23 years feeding in the sediment and growing into 2 – 4 foot, silver-bronze adults before heading to the ocean to spawn. Spawning eels congregate in the weed-choked expanse of ocean south of Bermuda called the Sargasso Sea.

Each adult female produces upwards of 15 million eggs. It is presumed that all adults die after spawning beneath that thick algae mat. American eel populations are declining. Overfishing and dams have hurt these migrants. The species was considered for federal endangered species status in 2007, but was not listed. Eels can travel successfully for short distances on land, particularly during damp weather. Eelways have been constructed at some tributary dams to improve their migratory success.

American shad are currently the most numerous migratory fish on the Connecticut River. Adult shad are green-gold, nearly two feet long and can weigh up to 5 lbs. Females (roes) are larger than males (bucks). Peak migration occurs during May, but the run continues through late-June. American shad spawn in East Coast rivers from central Florida to Newfoundland. Shad enter the Connecticut each spring beginning in mid-April. The vanguard of their upstream migration corresponds roughly with the blooming of the shadbush.

The spawning peak is reached when river temperatures reach 67 degrees F., at which point the fish stop their upstream migrations to spawn. Once river temperatures hit 70 degrees, upstream migration ceases altogether. Only half of the migrating Connecticut River shad die upon spawning. Many head back to the sea and will return to spawn up to three times. During midsummer the entire East Coast shad population migrates to the Bay of Fundy to feed.

Shad numbers have experienced steep declines on the Connecticut in the past decade. From a high count of 720,000 fish passing Holyoke dam in 1992, the average for the seasons 2005 – 2007 was 143,000 fish. Historically, shad have spawned as far inland as Bellows Falls, Vermont, 173 miles from the Atlantic.

Blueback herring are sleek, metallic-blue fish, under a foot in length. Blueback herring return to the main stem of the Connecticut River from mid-April through June. Considered bait fish, these migrants travel as far upstream as Vermont’s Vernon Dam, 134 miles from Long Island Sound. They spawn in quick, shallow currents of the main stem river and its tributaries; then feed in the Connecticut’s currents until fall, when they return to the sea.

Alewives are close relatives of blueback herring and difficult to distinguish from them. Alewives are lighter in color and have larger eyes than bluebacks. They migrate into the Connecticut River and its lower tributaries each spring, moving to the slow waters and ponds where they will spawn between March and June. Their upstream migration does not reach into Massachusetts waters. Like their blueback counterparts, alewives are experiencing steep declines. Though dam removals, fishways and other restoration projects have opened up some of their historic spawning habitat, alewife populations have been damaged by overfishing, pollution, and spikes in predatory fish populations.

Atlantic salmon are over two feet long and weigh about 8 pounds when they return from the Atlantic to spawn for the first time. Born in freshwater rivers, they spend the first two years of their lives growing and feeding there. This coldwater species then heads to the sea to spend several years feeding off the Greenland coast before returning to the freshwater rivers of their birth to spawn. The Connecticut River strain of Atlantic salmon became extinct in the early 1800’s. In 1967 an effort to create a new strain of migratory salmon on the Connecticut began. Click here to learn more about the CT River Atlantic Salmon Commission.

Sea lamprey are mottled brown, 2 – 3 foot long, eel-like fish that are born in freshwater rivers and spend 3 – 5 years in freshwater before heading to the ocean to feed and mature. Once in the ocean sea lampreys become parasitic, locking onto ocean fish (including whales and sharks) with their jawless, sucking mouths, and draining nutrition (primarily blood) from them. After spending 1 – 3 years as ocean parasites, sea lamprey head back to the closest freshwater river or stream, cease feeding and—though now blind and toothless—migrate upstream where they spawn and die. Lampreys evolved early in earth’s history, probably appearing at about the same time as the first plants appeared on land. They showed up even before dinosaurs appeared and look very much the same today as they did way back then.

To learn more, visit the new Migratory Fish website developed by Connecticut River Conservancy and regional conservation partners.