Connecticut River Coordinator's Office
Northeast Region
Photo of a volunteer stocking fry in the Sawmill River - Photo credit:  Draper White
Photo of a volunteer stocking fry in the Sawmill River. Credit: Draper White

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  • In late autumn, the female salmon buries fertilized eggs in stream bottom gravel nests called redds.

  • The eggs hatch into alevin or sac fry in the late spring, and the yolk sac is gradually absorbed.

  • Three to six weeks after hatching, alevins emerge from the gravel to seek food and are called fry.

  • Fry quickly develop into parr with camouflaging vertical stripes. The parr are two inches long. They feed and grow from one to three years in their native stream before becoming smolts.

  • Smolts are silver colored and approximately 6 inches long. In the spring, smolt body chemistry changes; they now weigh about 2 ounces and are ready to enter salt water. They migrate to the ocean where they will develop in about two to three years into mature salmon weighing about 8 to 15 pounds.

  • The adult salmon begin returning in the spring to their native stream to repeat the spawning cycle.

  • Spawned-out salmon, called kelts or black salmon, return to the ocean or overwinter in the river.

Atlantic salmon spawn in October and November, burying their eggs in prepared gravelly-cobble areas in streams called redds. Most females lay a total of 7,000 to 8,000 eggs in two or more redds. A steady supply of clean, well oxygenated water is critical to sustain these eggs. The eggs remain in the gravel throughout the winter before hatching in the spring. Newly hatched salmon, called sac fry, obtain food from their attached yolk sac. The salmon emerge from the redd, primarily from April to June, when the yolk sac has been completely absorbed. Feeding activities begin at this time. Salmon fry, approximately one and one quarter inches long at emergence, quickly set up feeding territories which they defend from other fish. Growing salmon prefer stream habitat lined with cobble-sized stone and clean, cool (60-70o F) water that is free of sediment. Fish are found in riffles and along the interface of fast moving water, under overhanging cover and generally toward the bottom of the water column.

Fry that have spent their first summer in the stream where they hatched are three to four inches long by fall and are called parr. After one full year in freshwater, the parr will have grown to a length of four to six inches. Parr remain in freshwater for a period of one to three years. The freshwater residence period is largely dependent on growth rate. The fastest growing parr, usually from warmer, more productive tributaries, spend only one year in freshwater. Slower growing parr, often from colder, less fertile tributaries, spend three, or rarely, four years in freshwater. Most parr in the Connecticut River basin spend two years in freshwater. During their first fall, parr may disperse widely from their first summer location to seek new habitat.

Parr destined to leave the freshwater environment the following spring begin a process called smoltification during the preceding winter. Pronounced physical changes occur during the spring after salmon reach a size suitable for migration to the sea, six to eight inches or more. These changes allow juvenile salmon to adapt to life in marine waters. Throughout the smoltification process a series of behavioral, physiological, and morphological changes occur that transform young salmon from territorial, bottom-dwelling, freshwater fish to schooling, saltwater fish. Juvenile salmon leaving for the ocean are called smolts. Smolts lose the dark vertical stripes, parr marks, on their sides and become bright silver in color. Smolts migrate to Long Island Sound from April through June. Some smolts may commence pre-smolt movement in the fall to start their long migration. Because the Connecticut River is so long, this is believed to have been an important adaptation of the original upriver stocks of Connecticut River salmon.

Connecticut River smolts move eastward around Cape Cod and begin a long migration northward along the coast after reaching Long Island Sound. The salmon eventually arrive at waters off of the west coast of Greenland where they share feeding grounds with other Atlantic salmon from North America and Europe (Figure 3). Most Connecticut River salmon return to spawn after residing in the ocean through two sea winters (2SW). A few salmon, called grilse, return after spending only one winter at sea (1SW), and others wait until after their third sea winter to return (3SW). The average 2SW salmon grows from six inches long and weighing about two ounces as a smolt entering Long Island Sound to about 30 inches and 10 pounds as a returning mature salmon. Grilse (1SW) average about four pounds and 3SW salmon often weigh more than 15 pounds.

Figure 3. Ocean Migration of Atlantic Salmon.
Map of ocean migration of Atlantic salmon.

Adult salmon return to the Connecticut River primarily in May and June. In the freshwater environment, the color of the adult salmon slowly changes from silver to a very dark color. The salmon attempt to reach their natal streams, where they spend the summer holding in deep, cold pools before spawning in the fall. From the time they enter the freshwater until spawning, often six months later, the salmon do not feed; feeding begins after they return to saltwater in the fall or spring. Atlantic salmon, unlike Pacific salmon, do not die after spawning, though many die as a consequence of the rigors of the upriver migration, the spawning effort itself, and not feeding for up to one year while in freshwater. Adults that survive the rigors of migration and spawning are called kelts. Kelts return to the ocean in late fall or early spring, at which time they regain their silver color. A small percentage of salmon survive several spawning runs, alternating between freshwater and marine environments. Repeat spawners and grilse are valuable to the salmon population for maintaining genetic variability and providing a buffer for all sources (fresh and salt water) of mortality affecting the predominant 2SW year class.

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Last updated: September 13, 2010
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