Note:  To maintain consistency in terminology, most definitions are pulled directly from the 2005 Final Recovery Plan for the Gulf of Maine Distinct Population Segment and the 2010 Annual Report of the U.S. Atlantic Salmon Assessment Committee. Definitions of genetic terms are from Allendorf and Luikart (2007)


Habitat with No Access (Does not meet recovery criteria standard): Habitat above an artificial barrier (dam or road stream crossing) where the barrier is defined as severe.

Habitat with Impeded Access (Does not meet recovery criteria standard): Habitat above an artificial barrier where the barrier impairs a salmon’s natural ability to pass the barrier and therefore prevents some passage. This habitat is above Potential Barriers.

Habitat that is Accessible (Meets recovery criteria standard): At a minimum, the accessible habitat must allow for upstream and downstream movements of parr that seek out suitable habitats for feeding and sheltering; downstream movements of smolts during the spring migration; and upstream and downstream movement of adults that seek out habitats for spawning and resting.  To meet the recovery standard, habitat must fall under one of the following categories: 

1)       Accessible above a dam with upstream and downstream passage that does not preclude recovery:  Any dam that has received an incident take statement (pursuant to section 10 or section 7 of the ESA) for continued operations of that dam has undergone an analysis that considers the ongoing effects of that dam.  Thus, if the dam is covered under either section 7 or section 10 of the ESA, then the dam must attain sufficient performance standards to ensure that it does not jeopardize the continued existence of the GOM DPS both in terms of the immediate effects (effects on survival) and long term effects (effects on recovery potential).

2)      Accessible above stream crossings (e.g., culverts) that are set at the correct elevation using stream simulation (  This approach to designing crossing structures creates structures that are as similar as possible to the natural channel.  When channel dimensions, slope, and streambed structure are similar, water velocities and depths also will be similar.  Thus, the simulated channel should present no more of an obstacle to aquatic animals than the natural channel because they tend to have natural streambeds throughout, and span the channel at least 1.2 times the bankfull width.

Habitat that is Fully Accessible (Meets recovery criteria standard):  Habitat where there are no artificial barriers from that point to the ocean.

Alevins: The period after hatching when the salmon feeds only on the yolk sac.  Alevins are buried within the substrate of the stream bottom. This is the same stage known as “sac fry.”

Anadromous:  A term to describe fish that are hatched and reared in fresh water, migrate to salt water to feed, and then migrate back to fresh water to spawn.

Annual Spawning Escapement: Salmon that return to the river and successfully reproduce on the spawning grounds in a given year.


Barrier: Does not allow for upstream passage.

Partial Barrier:  May preclude upstream and/or downstream passage at certain stream flows or at certain times of the year.

Black salmon: An adult salmon that has already spawned and is still found in the freshwater reaches of the river between November of the year of spawning until the salmon returns to sea the following year. Also known as kelt.


Captive:  Adults produced from wild parr that were captured and reared to maturity in the hatchery.

Domestic broodstock: Salmon that are progeny of sea-run adults and have been reared entirely in captivity for the purpose of providing eggs for fish cultural activities.

Sea-run:   Atlantic salmon that return to the river, are captured alive, and held in confinement for the purpose of providing eggs for fish culture activities.

Conservation spawning escapement: Number of returning adults needed to fully use the spawning habitat.

Critical Habitat: From ESA section 3(5)(A), 16 U.S.C. 1532(5)(A):   Specific areas within the geographical area occupied by the species at the time of listing, in which those physical or biological features are found that are essential to the conservation of the listed species and may require special management considerations or protection. Critical habitat may also refer to specific areas outside the geographical area occupied by the species at the time of listing that are essential for the conservation of a listed species.

Diadromous:  Fish that regularly migrate between freshwater and seawater. This category includes anadromous, catadromous and amphidromous fishes such as sea-lampreys, sturgeons, salmons, etc[DK2] . 

Effective Population Size: The size of an ideal population that would experience the same loss of genetic variation, through genetic drift, as the observed population.

Entrainment: Involuntary movement of fish into a turbine or other environment that causes high mortality.

Eyed egg: The egg stage from the appearance of faint eyes until hatching.


Sac Fry: The period from hatching until end of primary dependence on the yolk sac.

Feeding Fry: The period from the end of the primary dependence on the yolk sac (initiation of feeding) to June 30 of the same year.

Fed Fry: Fry stocked subsequent to being fed an artificial diet. Often used interchangeably with the term “feeding fry” when associated with stocking activities.

Unfed Fry: Fry stocked without having been fed an artificial diet or natural diet. Most often associated with stocking activities.

Grilse:  A 1SW salmon that returns to the river to spawn. These fish usually weigh less than 5 pounds.

Hatchery Reared: Atlantic salmon of hatchery-origin that are stocked into the wild as smolts or adults.

HUC 10: USGS Hydrologic Unit Code having 10 digits and delineating watersheds between 40,000 and 250,000 acres in size.

Kelts:  An adult salmon that has already spawned and is still found in the freshwater reaches of the river between November of the year of spawning until the salmon returns to the sea the following year. Also known as black salmon.

Landlocked salmon: Non-anadromous Atlantic salmon, i.e., fish that do not migrate away from rivers upon maturity.

Metapopulation:  A collection of spatially divided subpopulations that experience a certain degree of gene flow among them.

Naturally Reared: Includes fish originating from wild spawners and hatchery eggs, fry, and parr.  Egg and fry stocked salmon are not given an external mark, so when they return as adults, it is not possible (except for genetic testing) to differentiate them from wild salmon.

Parr:  Life history stage immediately following the fry stage until the commencement of migration to the sea as smolts; parr are characterized by 8 to 11 vertical, dark pigmented

bars (known as “parr marks”) on their sides.

Precocious parr: An Atlantic salmon that becomes sexually mature in fresh water without ever going to sea.

Redd: Nest where female salmon lay eggs. Typically covered with gravel.

Repeat Spawners: Salmon that return numerous times to the river for the purpose of reproducing. Previous spawner.

Smolt:  An actively migrating young salmon that has undergone the physiological changes to survive the transition from fresh water to salt water.

Smoltification: The process by which parr change into smolt. This includes osmoregulatory changes that allow the fish to survive in salt water.

Straying: Fish spawning in a stream other than the one in which they hatched.

Stakeholder: Any group that is interested in Atlantic salmon recovery that is not the USFWS, NOAA, MDMR, or PIN.

Stocked Salmon: Salmon that have had artificial spawning or rearing techniques applied at some point in their life cycle or originate from intentional releases to the wild.

Weir: A structure across a river channel that obstructs the free passage of fish and is used for the purpose of taking or facilitating the taking of fish.

Wild Salmon: Salmon that have spent their entire life cycle in the wild and originate from parents that were also spawned and continuously lived in the wild.

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