One of the most interesting parts of nature is migration. If you really think about it, it’s incredible how animals know where to go every time they migrate, by simply sensing where their destination is. Humans, though we have evolved to such an advanced point, would struggle to return to that innate sense of direction found in any migrating species.
Salmon, however, seem to have multiple ways of sensing their home whether it be smell or magnetic pull. Their yearly migration is a sight to see, and one that many species, including humans, tend to take advantage of. The fishing is good if the fish are present, right? Even if not for fishing, there are still many advantages to knowing the migration paths of these incredible fish. This raises the question of how they migrate. Do they swim upstream or downstream?
To understand this question and the answer accompanying it, it’s important to know why a salmon migrates over such incredible distances. Some salmon swim all the way from Japan to the coast of Seattle. By knowing why they migrate, it becomes easier to understand why they push themselves so heavily. So to the question of upstream or downstream, the answer is simple. Salmon swim upstream to get back to their natal site. But knowing why will make the situation much clearer.
Why Do Salmon Return to Their Natal Site?
Every year when it’s time to mate and give birth, the salmon return from their feeding grounds to the places where they were born. For some, this can mean a trek all the way across the Pacific Ocean. For others, it’s a simple swim back up the river. For all, it means a tough journey upstream almost the entire way. Why do they subject themselves to such strife just to return to a spot to mate and give birth?
Think of it this way – the salmon know the place where they were born is a good, safe spot for their offspring. It was enough to keep them alive, so it will work well for their offspring as well. There’s no point in spending valuable time searching for a random river that might not be suitable for the young salmon. By returning to their natal site, the salmon are able to guarantee that the birthing location will be safe and have the tools needed to support this new life.
On top of this safety and proven effectiveness, it’s an easy spot to return to. Salmon are able to migrate for miles in order to return to the spot where they were born. It’s the easiest spot for them to navigate to and is almost a sixth sense for them. Finding a new breeding ground would be much more difficult for them, so they simply use their senses and return to their own natal sites. These natal sites are different for varying species of salmon, and even different between colonies.
How Do They Know Where to Go?
This is the question that comes with every migrating species. How do they know which direction their destination is, and what the best path to take is? For some, they’ve been doing it for years and have memorized the journey. For others, like the salmon, it’s all about their sense of smell with a little help from the magnetic pull of the earth. The latter applies to ocean salmon as it helps guide them between destinations. When they return to their natal sites, the pull is stronger.
As for the sense of smell, the birthing sites have a distinct smell that young salmon memorize when they are first born. When they leave, that unique smell sticks with them so that they can follow it when it’s time to give birth. By using their keen sense of smell, they can follow it like a map to return to their natal site. The stronger the smell, the more they’ll push to get back. Once the smell weakens, they know they’ve gone in the wrong direction and turn around.
So, Upstream or Downstream?
When returning to give birth, a salmon will fight against the current nearly the whole way and swim upstream. This determination to get home is what pushes a salmon to fight the whole way against the current. For many migrating species, the journey they take is dangerous and full of difficulties.
For salmon, one of those difficulties is the constant push against the current to return to their natal site. Imagine the site of salmon jumping up waterfalls – that’s essentially what their entire journey is.
For some salmon, that journey ends early, and they don’t make it. Whether the press upstream was simply too much for them, or a pesky bear was waiting atop that waterfall to bring them in for a quick snack, many won’t survive the journey. For those who do, their offspring will be born and will accompany them to the feeding grounds when ready. The journey is a yearly one and asks a lot of the salmon. However, that natural push to reproduce and continue life is strong for salmon.
Times When a Salmon Swims Downstream
There are a few times, when migrating back to their natal sites, when a salmon will swim downstream, though it’s not when they’re making forward progress. As we mentioned, many salmon follow their sense of smell to return to the natal sites to give birth. However, sometimes, when swimming upstream, they can make a wrong turn and end up losing that smell. The smell is what drives them to keep pushing against the current and swim upstream.
Once that smell is gone, the salmon loses the drive to return home to give birth. Eventually, after swimming downstream for a bit, that smell returns, and they find a different path. Whenever a salmon loses the smell of their natal site, they swim downstream until the smell comes back.
For 99% of their journey back, the salmon will fight the current and swim upstream, driven by their sense of smell and their need for a safe and secure birthing site.