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NATURAL HISTORY

GULF OF MAINE ATLANTIC SALMON } Salmo salar
FAMILY: Salmonidae

DESCRIPTION: Adult salmon typically weigh from eight to 15 pounds or more and reach up to three feet in length. Young salmon called parr have eight to 11 vertical dark “parr marks” on their silvery sides. After smolting (adjusting to saltwater) and entering ocean waters, juvenile salmon obtain a silver coloration with small, dark dorsal spots. Spawning adult salmon darken to a bronze color after entering freshwater and spawning.

HABITAT: Atlantic salmon require coastal rivers with suitable gravels and clean-flowing water for spawning, and freshwater nursery habitat in riffle areas with good cover from predators for rearing. Adult salmon feed and mature at sea.

RANGE: Gulf of Maine Atlantic salmon inhabit rivers and streams in Maine from the lower Kennebec River north to the Canadian border. The salmon's range in Maine at least encompasses the Dennys, East Machias, Machias, Pleasant, Narraguagus, Ducktrap, Kennebec, and Sheepscot rivers, as well as Cove Brook.

MIGRATION: Atlantic salmon leave Maine rivers in the spring and reach Newfoundland and Labrador by midsummer. They spend their first winter at sea in the area of the Labrador Sea south of Greenland. After the first winter at sea, a small percentage return to Maine while the majority spend a second year at sea. After a second winter in the Labrador Sea, most Maine salmon return to rivers in Maine, with a small number returning the following year.

BREEDING: Atlantic salmon breed in October and November. The female chooses the nesting site and digs the nest, called a redd, and then rests while the male continues to court her and drive away other males. When the redd is finished, the male aligns himself next to the female, the eggs and sperm are released, and the eggs are fertilized externally. On average, a female deposits 700 to 800 eggs per pound of her body weight. She then covers the eggs with gravel, rests, and repeats the operation — creating a new redd, depositing more eggs, and resting again until spawning is complete, which may take a week or more. Some Atlantic salmon die after spawning, but many survive to spawn a second time; a very few salmon spawn three or more times.

LIFE CYCLE: Atlantic salmon are anadromous, typically spending two to three years in freshwater, migrating to the ocean for another two to three years, and then returning to their stream of birth to spawn during the fall. Fertilized eggs hatch in March or April and become “fry,” remaining buried in the gravel for about six weeks. The fry emerge from the gravels around mid-May, quickly dispersing from the redds. The juvenile salmon live as parr for two to three years in freshwater. Parr finally undergo a physiological transformation called smoltification that prepares them for life in saltwater, leaving Maine rivers in the spring to feed and mature at sea.

FEEDING: Fry feed on plankton and small invertebrates. Juvenile salmon feed mainly on aquatic insects, mollusks, crustaceans, and fish. Adult salmon at sea feed on squid, shrimp, and fish. Adults do not feed in freshwater during spawning.

THREATS: Atlantic salmon are threatened by excessive and unregulated water withdrawal, fish diseases, interbreeding with and competition from escaped farm-raised salmon, predation by introduced fish species, pesticides, and sedimentation and other impacts to stream habitat from development, agriculture and logging.

POPULATION TREND: In fewer than 300 years, the Atlantic salmon's numbers have decreased by 90 percent. Wild salmon have been extirpated from at least 14 small coastal rivers in the Gulf of Maine, and populations south of the Kennebec River have been extirpated. Only eight rivers in the Gulf of Maine are known to still support wild Atlantic salmon, and at substantially reduced abundance levels. In 2004, total adult returns to the eight Maine rivers were estimated to range from only 60 to 113 salmon, and no adult fish were documented in three of the eight rivers.

 

Photo courtesy Flickr Creative Commons/
mineobskuriteter