The males of some species may change their body shape and develop a hooked snout, humped back, and elongated teeth, which are used to attract a mate and defend spawning territory. All adult salmon die after spawning, and their bodies decay, thus providing nutrients to future generations of salmon.
Salmon change color to attract a spawning mate. Pacific salmon use all their energy for returning to their home stream, for making eggs, and digging the nest. Most of them stop eating when they return to freshwater and have no energy left for a return trip to the ocean after spawning.
How do salmon spawn?
Salmon spawn in river systems with a very strong current, as their fast-flowing freshwater provides a lot of oxygen for their young. During their way upstream, the salmon keep their feeding activity to a bare minimum and burn through all of their bodily energy reserves in order to make it to the spawning grounds.
At the beginning of spring, as temperatures begin to rise, bass begin to feed heavily in preparation for the spawn. Salmon spawning is one of the most incredible natural events in the world and is referred to as a salmon run.
How do salmon know where to return to spawn?
Salmon come back to the stream where they were ‘born’ because they ‘know’ it is a good place to spawn; they won’t waste time looking for a stream with good habitat and other salmon. Scientists believe that salmon navigate by using the earth’s magnetic field like a compass. When they find the river they came from, they start using smell to find their way back to their home.
Young Atlantic salmon spend two to three years in their home river before going on a one to three year journey in the North Atlantic where they grow into an adult. They travel over 6,000 miles before coming back home to spawn. They sometimes swim 200 miles up the river to find their preferred places to spawn.
Managers regulate the fishery based on escapement goals to ensure harvests are sustainable. Salmon fishery management largely relies on in-season assessment of how many salmon return to fresh water to spawn . Managers set harvest levels based on these returns.
Why do salmon have different body shapes?
When salmon were in the ocean, they had a similar body shape. Once they turn to the rivers to spawn, you can see physical changes in their body shape. The males become deeper while the females have a more slender body shape. But females can expand their bellies so they can store their eggs.
What happens to salmon when they transition from saltwater to freshwater?
Salmon undergo a physical transformation during their transition from the saltwater environment back to the freshwater home of their birth. This transition affects the appearance of the fish very radically. Not only do they stop feeding, but they also undergo a color and shape change.