Have you ever wondered how that piece of wild salmon got to your dinner plate? Just consider yourself lucky, because statistically, that fish was lucky to have even been born. The journey salmon take to get to fresh water in order to spawn can be up to 900 miles horizontally and 7,000 feet vertically. This perilous journey causes extremely high mortality rates–– over 90% since 2000––but why is this path to breeding grounds so challenging and necessary?
Most people know that salmon jump up waterfalls, and nature documentaries often portray vulnerable salmon in mid-air only to be caught by a waiting bear. This however, is only one of the numerous challenges that these fish face when breeding time comes around. Salmon spend about 1-2 years in the ocean feeding and growing strong in anticipation of this journey. Fresh water washes away at the salmons’ scales, so while in the ocean, salmon must develop tougher skin which will slowly wear away along their fresh water journey.
The journey itself from ocean to calm freshwater is long and dangerous, but breeding is built into the DNA of salmon. Knowing that their skin will soon wear away, the salmon must swim quickly to prevent its protective layer from completely falling off. Thus, only the strong swimmers and the fish with tough scales survive this portion of the journey. Adding to the challenge is all the jumps they must take, with or without bears, because salmon often just jump straight up and do not make it past the ledge. All this requires immense effort, and some fish do not have the energy to make it up all the jumps. And, despite having made it past every obstacle in their way, some salmon finally reach the calm breeding grounds, yet are infertile and cannot breed anyways.
In order to counteract these increasingly challenging obstacles, salmon have created their own form of reversing the odds. Scientists from the Atlantic Salmon Federation have placed tracking devices on salmon to see where they were born and where they return to breed. Year after year, about half the salmon return home and the other half breed along another branch of the river, but still relatively close by to their original birthplace. If all salmon returned to the same place, no new breeding grounds would be discovered. Where salmon breed adds to the natural selection aspect of their lives because the new location could provide a better environment for the spawn to survive, allowing for stronger salmon and continuing to facilitate evolution. Thus, the location of salmon breeding helps them to maintain a strong population considering the odds against them.
Next time you think about the challenges faced by animals to breed, consider the truly perilous journey that salmon must encounter, simply to lay their eggs. For these fish, simply being alive is considered against the odds of nature, and only through determination and exploration can they continue to stay alive and return to breed year after year.