Salmon swim up rivers to reproduce because it is their reproduction instinct that drives them to return to the areas where they were born to spawn and perpetuate their species.
The salmon begins its life in freshwater rivers, where the eggs laid in gravel develop into fry, then into small fish called smolts. After several months of growing quietly there, it transforms into a smolt and heads out to sea. Once in the ocean, it gorges itself, grows for several years, and then one day, driven by an irresistible urge, it embarks on a journey to swim upstream to its native river. This migration, often spectacular and incredibly risky, can stretch for hundreds of kilometers upstream to precisely find the river where it was born in order to spawn. After this feat, many salmon die, their journey primarily serving to ensure the survival of the next generation.
Salmon are born and grow for a while in freshwater, but they spend almost their entire adult life in the ocean. However, they return to their birthplace to spawn, thanks to their highly developed olfactory memory. This upstream journey allows them to provide their offspring with a more secure environment: in rivers, there are fewer predators for their eggs and fry. The fresh, well-oxygenated water of rivers offers ideal conditions for the development of embryos. Another major advantage is less food competition for the young, who can quietly grow before heading off to the ocean themselves. Of course, all this has been carefully selected by evolution, which favors those capable of finding their natal river and successfully making this risky but necessary journey to ensure the survival of their species.
Salmon must face several natural obstacles during their journey upstream. They often encounter strong currents that impose exhausting efforts on them; they navigate difficult rapids, sometimes jumping out of the water nearly three meters high! Not to mention the numerous predators along their way: bears, eagles, and humans who take advantage of the fish gathering. In addition to these natural dangers, there are artificial obstacles, such as dams, which prevent or significantly complicate the salmon's progression to their usual spawning grounds. These challenges make this journey incredibly perilous, and unfortunately, many salmon do not survive it.
When salmon swim upstream, they bring a true wealth to the entire ecosystem. By spawning and then dying in freshwater, their bodies become a valuable source of nutrients, particularly nitrogen and phosphorus, essential for the growth of surrounding aquatic and terrestrial plants. These nutrients boost the productivity of waterways and enhance the overall health of the surrounding forest, even benefiting nearby trees that absorb some of them. This, of course, attracts a variety of animals such as bears, birds, and various mammals that take advantage of this seasonal feast. Ultimately, salmon spawning in rivers creates a positive domino effect, enriching the entire food chain and maintaining healthy biodiversity.
During their migration, some salmon can travel up to 3,000 kilometers and overcome obstacles that can reach several meters in height in order to return precisely to their birthplace.
After laying their eggs, the majority of salmon species die naturally, thus providing valuable nutrients that sustainably fertilize the surrounding aquatic and terrestrial ecosystems.
Some predators, such as bears, eagles, and even wolves, specially adapt their behavior and hunting schedule to coincide with the migration of salmon upstream.
The presence or absence of salmon migrating upstream is considered a reliable indicator of the quality and overall health of that aquatic environment.
In general, salmon stop feeding when they begin their journey upstream to spawn. They then rely solely on their fat reserves accumulated in the sea, which leads to their gradual weakening during migration.
During their migration, salmon undergo significant physiological transformations known as smoltification when heading out to sea and reproductive changes when returning to freshwater. These adaptations include changes in color, body morphology, and the development of pronounced jaws in males, facilitating reproduction and adaptation to their various habitats.
During this upstream journey, salmon encounter various natural obstacles (rapids, waterfalls, predators) and anthropogenic challenges (dams, pollution, intensive fishing). These trials require a great deal of endurance and often result in the death of many individuals who nevertheless attempt to reach their spawning grounds.
The migration duration of salmon can vary greatly depending on the species and the distances to be covered. Some salmon migrate for several weeks or even months, sometimes traveling hundreds or even thousands of kilometers to reach their spawning site.
Most salmon have a strong 'homing' instinct that allows them to precisely find their birth river through a combination of scents, currents, and the Earth's magnetic field. However, a few individuals may exceptionally migrate up a different river.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
