Trout & salmon · Freshwater
Atlantic salmon
Salmo salar (anadromous)
Anadromous Atlantic salmon hatch and rear in freshwater, migrate to sea, and return to natal river systems to spawn.
Also called grilse (an adult returning after one winter at sea; DFO uses a 63 cm break), kelt (a post-spawning adult), sea-run salmon, sea run salmon.
- Flowing water
- Conservation-sensitive
- 4 of 4 overlays reviewed
- Reviewed 2026-08-27
Before you target this fish
Conservation-sensitive — presence is not permission
Wild sea-run Atlantic salmon are protected in the United States and commercial and recreational fishing is prohibited. This record is context-only and intentionally separate from landlocked Atlantic salmon fisheries.
Where this applies Wild anadromous U.S. Atlantic salmon; this does not describe landlocked or stocked fisheries.
The reviewed context, unedited
Conservation-sensitive context only. Biological presence is not evidence of a legal recreational fishery.
Rules for this fish change at a state line and sometimes inside one. Check the ones that apply to the exact water you are standing on before you act on anything here — this record is biology, not permission.
Take this somewhere
This page is the record. The reading is what happens when you add water, a season and a temperature to it — that is where the families below get ranked against each other instead of just listed.
Those three links carry the fish and nothing else. No conditions were declared on this page, so none travel, and the link says so rather than sending an empty reading.
The half nobody publishes
What this record does not know
Everything else on this page comes from a named agency or peer-reviewed source. This is the other side of that: the questions a reviewer went looking for an answer to and came back without, and the fields the record leaves empty because filling them would mean guessing.
It is here rather than at the bottom because a page that only shows what it knows is easy to read as a page that knows everything. For Atlantic salmon there are 20 of them.
Named by a reviewer
15Somebody looked for this and wrote down that they did not find it.
- Behaviour
Nobody has sourced:
- diel behaviour of returning adults in fresh water
- clarity response
- cold-front or barometric response with primary-source support
- angling-pressure response with primary-source support
- the Fraser et al. 1995 temperature threshold could not be read directly — the paywalled abstract was not reachable, so only the finding named in the paper's title is asserted here
- Identification
Nobody has sourced:
- regional color variation between river systems
- a documented maximum length or weight from an agency or peer-reviewed source
- a field key separating anadromous from landlocked fish on appearance alone (the sources reached give the same characters for both)
- Forage
Nobody has sourced:
- emerging_insects and terrestrial_insects — the catalog forage list carries both, but the agency sources reached say only 'invertebrates' and 'aquatic insect larvae' for parr and name neither emergence nor terrestrial drift, so both are omitted from primaryForage rather than asserted. This is the main reason this record is partial.
- crustaceans — the catalog list carries this class; the sources reached give 'plankton' at sea without resolving it to a crustacean record, so it is omitted
- season-by-season diet emphasis for parr
- quantitative freshwater diet composition
- Season
Nobody has sourced:
- run timing outside the Gulf of Maine — Canadian and European river timings are not covered here
- winter habitat use by adults that overwinter in fresh water, where that occurs
- kelt behaviour and survival between spawning and seaward drop-back
Absent from the record
5No reviewer wrote a gap here. The field is simply empty, which is its own answer.
- Presentation
No presentation family is reviewed for Atlantic salmon in flowing water. The record documents the fish there; it does not yet say how to fish for it there.
No species-specific weighting rule is reviewed for Atlantic salmon. Its ranking comes from the shared model — season, temperature, water type, holding and forage — with nothing added for this fish in particular.
- Water temperature
No agency or peer-reviewed temperature band for Atlantic salmon was found that a review would accept. The reading runs without one rather than borrowing a number from a related fish.
- Identification
No reviewed image. A photograph is only in this catalog when an agency or a named creator labelled the subject, and nobody has cleared one for this species yet.
- Population context
No regional population profile is registered. The species-level reading stands on its own; it does not silently become a local one.
Where the record puts it
Water and range
Flowing water
5 reviewed holding classes- Riffle-to-run transition
- Run
- Pool head
- Deep pool
- Tributary mouth
DepthLife stage governs depth: parr use shallow fast nursery water while returning adults use deeper pools and runs between migration movements.
Moving waterJuveniles use well-oxygenated riffle-run habitat; returning adults require connected river corridors, pools, and suitable gravel spawning habitat.
LightLight affects movement and cover use, but migration stage, discharge, temperature, and connectivity dominate freshwater positioning.
Thermal band
Temperature
No reviewed temperature band
Nobody publishes a preferred or active temperature range for Atlantic salmon that a review would accept. Borrowing one from a related fish would look like knowledge and behave like a guess, so the reading runs without it and says which parts of the answer that weakens.
How it uses water
Behaviour
Biological context only. Atlantic salmon are a conservation-sensitive record in this catalog and this dossier carries no targeting guidance.
This applies to the freshwater juvenile stage. Parr take invertebrates and some small fish from moderate-to-fast riffle water. The returning adult does not feed: USFWS states that once in fresh water, adult salmon cease to feed during their upriver migration and darken in colour, and Maine DMR describes adults ceasing to feed on entering rivers and seeking shaded, cool pools and springs. Any adult behaviour in the river is therefore migration, thermal refuge and spawning behaviour, not foraging.
For juveniles, and temperature-dependent. Fraser, Metcalfe and Thorpe (1995) report that low summer temperatures cause juvenile Atlantic salmon to become nocturnal — the switch between diurnal and nocturnal foraging in this species is temperature-dependent rather than fixed. Diel behaviour of returning adults in fresh water was not established in the sources reached; adults are non-feeding, so a foraging diel pattern does not apply to them.
Seasonal activitySmolts run to sea in mid-April to early June (Maine DMR, with peak movement around 50°F) or May–June (DFO). Adults return to Maine rivers from May through October, with 60–70% of the run entering fresh water before August and the peak in June. Early-returning fish spend nearly five months in the river before spawning in late October and November. Eggs incubate through the winter and hatch in spring.
Temperature-driven behaviourThe Gulf of Maine recovery plan puts the growing-season range at roughly 7–25°C, with sustained temperatures above 24°C impairing growth and overwinter survival and temperatures above 28°C harmful to juveniles. Upstream migration is inhibited above 22.8°C or below 5 ppm dissolved oxygen. Spawning requires 7–10°C. The catalog preferred band of 45–57°F sits inside the sourced growing-season range and does not contradict it. In summer, adults seek shaded, cool pools and springs and wait for water temperatures to drop.
Depth movementParr occupy riffle water 10–60 cm deep. Adults holding through the summer occupy deeper pools, with low late-summer flows in Maine rivers constraining movement between them.
Water levelAdults may hold for extended periods and undertake their final upstream movements after fall rains; upstream migration is driven by flow, temperature and olfactory cues, and low late-summer flows constrain movement.
CoverParr use gravel and rubble up to 20 cm in riffles. In winter, juveniles use rock and root-wad complexes and the quiet water formed by boulders, woody debris and stream edges. Adults in summer use shade, cool pools and spring inflow.
Predator avoidanceParr spend much of their time on the streambed among gravel and rubble; the winter shift into rock and root-wad complexes and boulder-formed quiet water is a shelter behaviour.
TerritoryParr are highly territorial in riffle habitat with gravel and rubble cover up to 20 cm, water depth of 10–60 cm and moderate-to-fast flow of 30–90 cm/sec.
Spawning (conservation context)Fall spawner. Spawning occurs mid-October through mid-November at 7–10°C (Gulf of Maine recovery plan) or late October through November (USFWS), with Maine DMR putting redd construction at temperatures falling below 50°F. Females excavate redds in coarse gravel or rubble in moving water — the recovery plan describes 22–76 cm of water flowing at 27–83 cm/sec over the redd — and deposit roughly 7,500 eggs, which incubate through winter. Post-spawning adults are kelts and may return to the sea. Spawning substrate, redds and any pre-spawn holding water are conservation context and are excluded from this record's habitat guidance; no spawning area, staging concentration or migration bottleneck is described here.
Where the general rule stops
- This record covers wild anadromous Atlantic salmon, not stocked or landlocked Atlantic salmon fisheries.
- Do not infer legal fishing opportunity from biological presence.
What it can eat
Forage
- Aquatic insects
- Emerging insects
- Terrestrial insects
- Small forage fish
- Crustaceans
Biological context only; this catalog withholds presentation guidance for Atlantic salmon. The load-bearing fact for this species is that the freshwater diet belongs to the juvenile stage alone. Emergent fry take plankton and small invertebrates; parr take invertebrates and some small fish; DFO gives aquatic insect larvae for juveniles. The returning adult does not feed in fresh water — USFWS states adults cease to feed once in fresh water during their upriver migration, and Maine DMR states the same. The adult marine diet (herring, alewife, rainbow smelt, capelin, sand lance and mackerel per NOAA; zooplankton, fish larvae and small fishes per DFO) is life-history context and has no freshwater application. Capacity is not a current hatch.
- Feeding style
- Opportunistic
- Feeding zone
- Mixed
By life stage
- Young of year
- Emergent fry feed on plankton and small invertebrates.
- Juvenile
- Parr feed on invertebrates and some small fish, taken in riffle habitat.
- Adult
- Does not feed in fresh water. At sea, feeds on plankton and on small fishes including herring, alewife, rainbow smelt, capelin, sand lance and mackerel.
Ontogenetic shiftPlankton and small invertebrates as fry, to invertebrates plus some small fish as parr, to a piscivorous marine diet as a post-smolt and adult, then to non-feeding on the return to fresh water.
Diet capacity is not proof that a hatch or prey event is occurring. Observed current forage still comes from a user observation or Hatch Match. For this species the rule carries an extra edge: the freshwater forage record here describes parr, not returning adults, and no forage record in this dossier is a targeting cue for a conservation-sensitive fish.
Through the year
Season
Winter
- Where they sit
- For juveniles: rock and root-wad complexes, and the quiet water formed by boulders, woody debris and stream edges. Eggs incubate in gravel through the winter.
- Movement
- Low. The recovery plan flags high mortality for large pre-smolt parr during the winter before outmigration, making winter shelter availability a recruitment constraint.
- Cover
- Structural shelter rather than the open riffle positions used in the growing season.
What would count against it
- treating winter parr shelter as target water
Conservation-sensitive record; presentation guidance is withheld in every season. Incubating eggs are in the gravel throughout this period.
Spring
- Where they sit
- Riffle habitat for parr — gravel and rubble cover up to 20 cm, 10–60 cm deep, 30–90 cm/sec flow. Smolts move downstream through the mainstem.
- Movement
- Smolt outmigration mid-April to early June, with peak movement around 50°F (Maine DMR) or May–June (DFO). Adult river entry begins in May.
- Temperature
- Growing-season range roughly 7–25°C.
What would count against it
- treating the smolt run as a fishable event
Smolt outmigration is a population bottleneck in its own right; no migration route, staging area or concentration is described in this record. Presentation guidance is withheld.
Summer
- Where they sit
- Parr in riffle habitat. Non-feeding adults in shaded, cool, deeper pools and at spring inflow, waiting for water temperatures to drop.
- Depth
- Adults deeper as the season warms; low late-summer flows in Maine rivers constrain movement between pools.
- Temperature
- Sustained temperatures above 24°C impair juvenile growth and overwinter survival; above 28°C is harmful. Upstream migration is inhibited above 22.8°C or below 5 ppm dissolved oxygen.
- Cover
- Shade, depth and spring inflow for adults; gravel and rubble in riffles for parr.
- Light
- Juveniles switch between diurnal and nocturnal foraging with temperature; low summer temperatures push juveniles toward nocturnal activity (Fraser et al. 1995).
What would count against it
- reading adult presence in a summer pool as feeding behaviour — returning adults do not feed in fresh water
Summer thermal refuge holds non-feeding, energetically committed adults. Disturbance here is a conservation issue, not an opportunity. Presentation guidance is withheld.
Fall
- Where they sit
- Adults move upstream after fall rains; spawning begins mid-October. Spawning substrate is conservation context and is excluded from this record's habitat description.
- Movement
- Final upstream movement is cued by flow, temperature and olfaction, often after fall rains.
- Temperature
- Spawning at 7–10°C; Maine DMR gives redd construction as temperatures fall below 50°F.
What would count against it
- using spawning substrate as holding water
- reading the run as an activity window
Fall spawner. Redds, spawning gravel and pre-spawn holding water are excluded from target guidance, and no spawning area or aggregation is named. Presentation guidance is withheld.
Late fall
- Where they sit
- Spawning continues into mid-November; post-spawning kelts drop back downstream and may return to sea. Eggs are in the gravel.
What would count against it
- assuming spawning has finished because the calendar has turned
Late-fall spawning overlap remains conservation caution, and kelts are in poor condition. Presentation guidance is withheld.
Spawning · Fall, Late fall
Adults return to cold gravel-bed rivers and streams to spawn in fall; migratory holding pools and redds are conservation context, not fishing guidance.
Recorded as conservation context. No spawning site, staging concentration or migration bottleneck is named anywhere in this catalog, because naming one is how a population gets fished out.
Telling it apart
Identification
What to look at
- Tail is forked; a brown trout's tail is square with almost no fork.
- Caudal peduncle is thin, and the fish is easily 'tailed' by hand — a brown trout's peduncle is thick.
- Vomerine teeth (roof of the mouth) form a single row of small teeth on the shaft with little to none on the vomerine head. Brown trout show a prominent zig-zag row on the shaft plus well-developed teeth on the vomerine head.
- Adipose fin is dark, and any spots on it are hard to see. A brown trout's adipose fin is larger, often orange-tinted, and often obviously spotted.
- Maxillary typically does not extend much past the eye; the jaw reaches the middle or rear edge of the eye rather than beyond it. A brown trout's maxillary usually extends past the eye.
- Spots are smaller, less defined and fewer than a brown trout's, with fewer reddish spots. Strongly golden or orange fish are brown trout.
- Average adult length
- Up to about 30 in (NOAA). DFO splits returns into grilse (one winter at sea, under 63 cm) and multi-sea-winter fish (over 63 cm).
- Common angling size
- Not a target species in this catalog. NOAA Fisheries states that commercial and recreational fishing for Atlantic salmon in the United States is prohibited, and the Gulf of Maine DPS has been federally listed as endangered since 2000. Maine statute (12 M.R.S. §6140-A) additionally makes any Atlantic salmon fishing catch-and-release with an unweighted artificial fly only, closed 16 October to 30 April. Where regulated fisheries exist in other jurisdictions, encountered sizes follow the local grilse / multi-sea-winter split.
- Typical weight
- Typically 8 to 12 lb (NOAA).
- Maximum documented
- The agency sources reached give a typical upper size of about 30 in and 12 lb rather than a documented record; no maximum documented size was found.
- Longevity
- Typical lifespan 4 to 6 years (NOAA): two to four years as parr in fresh water, one to three years at sea, then return. Repeat spawners occur.
What it gets confused with
- Brown trout
- The reliable set is the tail and peduncle (forked and thin on salmon; square and thick on brown trout), the vomerine teeth (single small row on salmon; zig-zag row with a developed head on brown trout), the adipose fin (dark and faintly marked on salmon; larger, orange-tinted and spotted on brown trout), and the maxillary (not much past the eye on salmon; past the eye on brown trout).
- Landlocked Atlantic salmon
- The same species and the same identification characters; this record covers the anadromous form. The two are separate catalog records because life history, run timing and freshwater feeding differ — landlocked fish feed in fresh water throughout life, while returning anadromous adults cease feeding on entering the river.
What follows from all of that
Presentation families
Flowing water
The record documents Atlantic salmon in flowing water but has no reviewed presentation family for it. Presence and a method are different claims and only the first one is made here.
What moves them for this fish
No species-specific rule is reviewed for Atlantic salmon. Its ranking comes from the shared model — season, temperature, water type, holding water, forage — with nothing added for this fish in particular. That is a gap, not a claim that nothing is special about it.
Where every sentence came from
Sources
Agency
Fisheries and Oceans Canada: Atlantic salmon — a remarkable life cycle
Used for identification; behaviour; forage; season. Read 2026-08-30, next check 2026-12-09.
Agency
NOAA Fisheries species page: Atlantic Salmon
Used for identification; behaviour; forage. Read 2026-08-30, next check 2026-12-09.
Agency
Used for behaviour; forage; season. Read 2026-08-30, next check 2026-12-01.
Agency
Maine Department of Marine Resources — Atlantic salmon sea-run species page
Used for behaviour; forage; season. Read 2026-08-30, next check 2026-12-01.
Agency
NOAA Fisheries: Atlantic Salmon (Protected) — ESA conservation and management
Used for identification; season. Read 2026-08-30, next check 2026-12-09.
Agency
Used for behaviour; forage. Read 2026-08-30, next check 2026-12-01.
Agency
NOAA Fisheries Atlantic Salmon protected species profile
Used for habitat, thermal band and presentation families. Read 2026-08-27, next check 2026-11-27.
Agency
NOAA Atlantic Salmon conservation and management program
Used for habitat, thermal band and presentation families. Read 2026-08-27, next check 2026-11-27.
Agency
Used for identification. Read 2026-08-30, next check 2026-12-09.
Agency
Used for identification. Read 2026-08-30, next check 2026-12-09.
Agency
Maine Revised Statutes Title 12 §6140-A, Atlantic salmon; method of fishing; season
Used for identification. Read 2026-08-30, next check 2026-12-09.
Agency
USFWS National Conservation Training Center — Atlantic salmon life history
Used for season. Read 2026-08-30, next check 2026-12-02.
Peer reviewed
Used for behaviour; season. Read 2026-08-30, next check 2026-12-01.
Synthesis
Atlantic salmon freshwater habitat literature synthesis
Used for habitat, thermal band and presentation families. Read 2026-08-27, next check 2026-11-27.
A source with no link predates the rule that one has to carry a URL. It is still a real citation and still checkable; it just takes a search rather than a click, and that is worth knowing before you rely on it.