Do Salmon Feed In Freshwater?
By Patrick Mc Erlean
The question of whether or not salmon feed in freshwater is one that has fascinated anglers for many years. It’s viewed by many as perhaps the greatest of all of the many mysteries associated with this wonderful king of fish. But is it really such a mystery, given all that we know about the migrating salmon? To answer this question properly we need to take a look at the life of the salmon and its journey from egg to adult fish.
I guess the first question to ask is, “Did salmon always migrate from rivers to the sea”? We can only speculate on the answer to that, but speculate is exactly what I’m going to do, so please bear with me for a couple of paragraphs!
I don’t think that it’s too big a stretch to presume that there was a time when salmon spent all of their lives in freshwater? I’d guess that the species started out relatively small but that, over time, their average size got to the point where the available food supplies were no longer enough to sustain their growing population. At that point some of the more adventurous salmon would have begun the search for greener pastures, which eventually led to the sea.
Right that is enough of the speculation! Let’s look at what we know about the salmon’s life journey. I’m not going to get into the detail on when eggs hatch etc because Michael Mc Glade has covered that very eloquently in his article on the River Moyola hatchery (see Hatching A Plan For The Moyola). Suffice to say that salmon go through various stages of growth, from egg, to alevin, to parr, to smolt and finally to adult salmon.
Perhaps one of the most wondrous aspects of this development process is that the salmon go through the various stages at varying rates! For example some parr will smolt within the first 2 years, whilst others will not smolt for 3 or 4 years. You can even see this variation in fish that are all from the same batch of eggs. Likewise the smolts spend varying lengths in the sea. They even come back to spawn at various times of the year, e.g. spring, summer and autumn salmon. This behaviour is also observable in kelts, which return to the sea at varying intervals. Presumably the reason for this is to guard against mass extinction? Even if a catastrophic event were to happen, not all of the fish would be impacted, thus ensuring the survival of the species.
A salmon leaves the river as a smolt when it has developed the salt secreting gills it needs to survive in the sea. At some point during its life at sea the salmon gets the urge to return to the river of its birth to spawn. This urge triggers a physiological change in the fish, which results in it effectively switching off its feeding mechanism, much like those animals that hibernate for the winter months. Prior to this physiological change, the salmon has fed for a number of years at sea, building up its fat reserves, and it is now prepared to go without food until it returns from spawning. These are pretty much established facts at this stage and are rarely disputed.
Firstly, why would a salmon feel threatened by another species, which is much smaller than itself? Surely they’d only be threatened by other salmon. Have you ever seen a bull chasing a bird which has landed in its field? The second reason for debunking the territorial theory is because one of the most common times for a salmon to take is when it is resting between periods when it is running. Surely if a salmon was being territorial it would be much more likely to defend its patch when it gets to its spawning ground? In fact, as we all know, when a salmon gets settled into its spawning lie it’s even harder to tempt, if anything!
I believe that salmon have two main goals when they enter the river. The first is to spawn. The second is to conserve energy so that they can make it back to the sea to resume feeding. In order to conserve energy, salmon will rarely move about in poorly oxygenated water. Of course there will always be the odd exception but in general that is the case. Water which is low or warm, or both, is often poorly oxygenated. Cold water can be well oxygenated but the fact that it is cold will stiffen up the fish’s muscles and therefore it will remain less active in order to conserve energy. After all it takes more energy to move about with cold, stuff muscles.