# Salmon — Facts, Threats & Conservation

*Salmo salar (Linnaeus, 1758)*

> The Atlantic salmon (Salmo salar) is Least Concern globally but Endangered in much of its southern range; anadromous fish threatened by dams, aquaculture, sea lice, overfishing and river pollution.

**IUCN status:** Least Concern globally (IUCN, 2018) — Endangered in parts of range  ·  **WARN range:** North Atlantic — rivers of Europe and North America; ocean feeding grounds off Greenland

## Quick facts
| Fact | Value |
| --- | --- |
| Length | Up to 150 cm; typically 60–80 cm |
| Life cycle | Anadromous — river to sea and back |
| UK trend | 50%+ decline since 1970s |
| Sea feeding | North Atlantic — primarily off Greenland |
| Aquaculture threat | Sea lice, disease, escapes |
| CITES | Not listed |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Actinopterygii
- **Order:** Salmoniformes
- **Family:** Salmonidae
- **Genus:** Salmo
- **Species:** Salmo salar (Linnaeus, 1758)

## Conservation status
- **Status:** Least Concern globally (IUCN, 2018). Endangered in England, Wales and southern Europe.
- **Population:** Millions globally; wild runs declining in most European rivers
- **Trend:** Decreasing across most of range
- **Assessed:** 2018
- **CITES:** Not listed under CITES

## Key facts: Salmon
- Atlantic salmon hatch in rivers, feed at sea and return to spawn in natal streams.
- Globally Least Concern but Endangered in England, Wales and southern Europe.
- Open-net salmon farms spread sea lice and disease to wild fish.
- Dams and weirs block upstream migration; bycatch in mixed fisheries kills adults.
- Salmon navigate by olfactory memory — pollution impairs homing ability.
- Dam removal and river restoration show measurable recovery in some systems.

## River birth, ocean life
Atlantic salmon begin life as eggs laid in gravel redds — nests dug by females in clean, oxygenated stream beds. Eggs overwinter; alevins emerge with yolk sacs attached. As parr, they develop vertical bars and hold territories in freshwater for one to four years before smolting — transforming for sea entry.

Smolts migrate downstream, adjusting osmoregulation for salt water. They feed in the North Atlantic — primarily off Greenland — growing rapidly on crustaceans and fish. After one to three years at sea, adults return to natal rivers, often between June and November, navigating by olfactory memory of stream chemistry.

Spawning adults develop hooked jaws (kype) in males and darken. After spawning, most die — nutrients from their bodies fertilise headwater ecosystems. A small proportion may survive to spawn again.

## Ecological keystone of rivers
Salmon transport marine nutrients into freshwater and forest ecosystems. Bears, otters, eagles and ospreys depend on salmon runs. Carcasses left by predators enrich stream banks with nitrogen and phosphorus, boosting tree growth and invertebrate production.

Declining salmon runs cascade through food webs. Pacific northwest forests show reduced growth rings correlated with collapsed salmon returns. In Scotland, otter and eagle populations track salmon abundance.

Clean, cold, fast-flowing water with gravel beds defines salmon habitat. Siltation from forestry and agriculture smothers eggs. Warm water from climate change and abstraction reduces oxygen and triggers stress.

## Aquaculture, dams and bycatch
Open-net pen salmon farming — concentrated in Scotland, Norway, Chile and Canada — produces millions of tonnes annually but threatens wild fish. Sea lice from farms infest passing wild smolts and adults at lethal levels. Escaped farmed salmon interbreed with wild fish, reducing genetic fitness. Infectious salmon anaemia and other diseases spread from farms to wild populations.

Dams and weirs fragment rivers — the River Thames lost salmon entirely after weir construction. Fish passes help but rarely achieve full connectivity. Hydropower turbines kill downstream migrants.

At sea, salmon face mixed-stock fisheries — nets and longlines catching multiple populations indiscriminately. Bycatch in trawl fisheries for mackerel and herring adds mortality. Illegal fishing and unreported catch persist in some North Atlantic fisheries.

## Conservation and recovery
The IUCN lists Atlantic salmon as Least Concern globally — a status critics argue masks regional collapse. UK populations are Endangered; southern European stocks Critically Endangered. North American runs vary from healthy in Alaska to Endangered in Maine.

Recovery tools include dam removal — the Penobscot River restoration in Maine reopened hundreds of kilometres of habitat — riparian planting, pollution control and transitioning aquaculture to closed containment systems. The NASCO convention coordinates North Atlantic management.

Anglers practice catch-and-release; some rivers are entirely protected. Hatchery supplementation remains controversial — hatchery fish may compete with or genetically dilute wild stocks.

## Salmon and the future of rivers
Salmon embody the connection between ocean health and river integrity. Saving wild salmon requires action across the full life cycle — from headwater gravel to open-ocean feeding grounds.

Climate change shifts ocean productivity and river temperature regimes. Southern range edges may lose salmon entirely within decades. Northern rivers may gain suitability — but net global habitat is projected to shrink.

Readers can support salmon through sustainable seafood certification, advocacy for dam removal and river protection, and choosing farmed salmon only from closed-containment or land-based systems. WARN publishes this salmon guide as free public education about a species whose struggle defines Atlantic river conservation.

## What WARN does
WARN publishes this salmon guide as free public education. Free-flowing rivers and sustainable fisheries benefit salmon, eels and entire freshwater ecosystems.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Salmon
### Are salmon endangered?
Globally Atlantic salmon are Least Concern, but populations in England, Wales and southern Europe are Endangered or Critically Endangered. Many runs have halved since the 1970s.

### Why do salmon return to the same river?
Salmon imprint on the chemical signature of their natal stream as smolts. Olfactory memory guides adults back to spawn — pollution can disrupt this homing ability.

### How does salmon farming affect wild salmon?
Open-net farms spread sea lice, disease and escaped farmed fish that interbreed with wild salmon — reducing fitness and increasing mortality of wild populations.

### What is bycatch for salmon?
Salmon are caught incidentally in mixed fisheries targeting mackerel, herring and other species. Unreported and illegal catch at sea adds mortality to already depleted stocks.

### Can salmon populations recover?
Yes, where causes of decline are addressed. Dam removal on the Penobscot River and river restoration in Scotland show measurable increases in returning adults.

### What is the difference between Atlantic and Pacific salmon?
Atlantic salmon (Salmo salar) may survive spawning and return to sea. Pacific salmon (Oncorhynchus species) die after spawning. Both are anadromous.

## Sources
- [IUCN Red List — Salmo salar](https://www.iucnredlist.org/species/19855/89921842)
- [Atlantic Salmon Trust](https://www.atlanticsalmontrust.org/)
- [NASCO — North Atlantic Salmon Conservation Organization](https://nasco.int/)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/salmon