Don's Home Science Biology Salmon

Life cycle:

A salmon's life cycle begins with eggs laid in freshwater streams where they hatch into tiny fish called "alevins" that live in the gravel; as they grow, they become "fry" and eventually transition into "smolts" which migrate to the ocean for 2-5 years to mature into adults; once ready to reproduce, they return to their natal streams, spawn, and then die, completing the cycle by providing nutrients back to the freshwater ecosystem through their decaying bodies. Key points: Starts in freshwater: Salmon eggs are laid in gravel nests ("redds") in rivers and streams.
Eggs are buried in gravel nests, called "redds", and salmon can stay in their eggs for several weeks to months until they hatch.

Early stages: After hatching, young salmon called "alevins" remain hidden in the gravel until they develop into "fry" that begin feeding. Migration to ocean: When ready, fry transform into "smolts" and migrate downstream to the ocean where they spend most of their lives growing. Return to spawn: Adult salmon eventually return to the same freshwater stream where they were born to spawn, after which they typically die. The Salmon Life Cycle - Olympic National Park (U.S. National Park Service) Jul 22, 2019 National Park Service Salmon Life Cycle and Seasonal Fishery Planning Oct 6, 2022 — After spawning, adult salmon die and their bodies provide nutrients for the freshwater ecosystem. Eggs are buried in gr... NOAA Fisheries Species & Lifecycle - Pacific Salmon Foundation And some, like Steelhead and Cutthroat, can spawn more than once. Despite these variations, we can still make some general observa... Pacific Salmon Foundation Show all

There are various theories about how this happens. One theory is that there are geomagnetic and chemical cues which the salmon use to guide them back to their birthplace. The fish may be sensitive to the Earth's magnetic field, which could allow the fish to orient itself in the ocean, so it can navigate back to the estuary of its natal stream.
Salmon have a strong sense of smell. Speculation about whether odours provide homing cues go back to the 19th century.[22] In 1951, Hasler hypothesised that, once in vicinity of the estuary or entrance to its birth river, salmon may use chemical cues which they can smell, and which are unique to their natal stream, as a mechanism to home onto the entrance of the stream.[23] In 1978, Hasler and his students found that the way salmon locate their home rivers with such precision was because they could recognise its characteristic smell. They further demonstrated that the smell of their river becomes imprinted in salmon when they transform into smolts, just before they migrate out to sea.[20][24][25] Homecoming salmon can also recognise characteristic smells in tributary streams as they move up the main river. They may also be sensitive to characteristic pheromones given off by juvenile conspecifics. There is evidence that they can "discriminate between two populati

Burst swimming
Sockeye salmon can swim at a speed of five or more body lengths per second, or at least 7.0 miles per hour, over short distances.
Swimming upstream
Salmon swimming upstream against a strong current will swim much slower. For example, sockeye salmon swimming up the Kenai River may swim at a speed of about one mile per hour.
Tagged salmon
Tagged salmon have been observed swimming between 15 to 50 miles per day. The Salmon that Were Born to Survive | Hakai Magazine
Salmon are known to be aggressive and territorial, and will defend their spawning areas from other fish. They can also jump up to two meters to cross obstacles in rivers.

Links:
Salmon Life Cycle and Seasonal Fishery Planning fisheries-noaa.gov