Why do salmon try and return to their birthplace even if it kills them?

Pacific salmon, including species like Chinook, Sockeye, Coho, Pink, and Chum, exhibit an extraordinary behavior known as natal homing or "the salmon run." They undertake extensive migrations, often swimming hundreds or thousands of miles across the open ocean, to return to the specific freshwater streams or rivers where they were born. This remarkable behavior is driven by an innate biological imperative and is crucial to their life cycle and reproductive success.

Biological Imperative:

1. Genetic Memory: Salmon have an extraordinary ability to remember the unique chemical and environmental cues of their natal stream. This information is encoded in their genes and passed down from generation to generation. As adult salmon approach their home river, they use these cues to navigate and find their way back with remarkable precision.

2. Spawning and Reproduction: Salmon return to their birthplace to spawn and reproduce. This behavior ensures that the next generation of salmon will be born in the same environment and habitat conditions that are optimal for their survival. Spawning in their natal streams provides suitable water temperature, oxygen levels, and substrate for egg development and survival.

Why It Can Be Deadly:

1. Challenging Journey: The journey back to their birthplace is often arduous and strenuous. Salmon navigate challenging rivers, waterfalls, and rapids, battling strong currents and overcoming physical obstacles. This strenuous migration consumes a significant amount of energy and can lead to injury or even death.

2. Predation and Exhaustion: During their migration, salmon become vulnerable to predators such as bears, eagles, seals, and other animals. Additionally, the physical demands of the journey, combined with the lack of food consumption during the migration, can lead to exhaustion and increased susceptibility to diseases.

3. Competition and Stress: As salmon congregate in their natal streams, they face competition for spawning sites and mates. This competition can lead to aggressive behavior, further increasing stress and energy expenditure. Moreover, the overcrowding can strain the resources of the ecosystem and make it harder for salmon to find suitable places to spawn.

Despite the risks and challenges, the overwhelming majority of salmon successfully complete their migration and return to their birthplace to reproduce. This behavior is deeply ingrained in their biology and essential for the continuation of their species.