What percent of introduced game fish (Chinooks, Cohos, Brown/Rainbow Trout etc.) reproduce naturally?

I was recently watching the Salmon run near Humber bay (in Ontario), and was wondering about this, I heard that no Salmon there reproduce naturally, most are milked for their eggs, then the young are raised in hatcheries and later released into the lake. Is that true? Or do some lucky fish find a mate, reproduce, and have their offspring make it back to the lake to successfully repeat the cycle without the influence of humans? If so does anyone know the approximate amount of fish that manage do this, is that even possible to measure? I’d really like to know, thanks!


It is a bit too complicated to give a set %. Many variables play in throughout the lives of these fish. You generally are talking about their entire life cycle. Pacific salmon in Lake Ontario surprised many biologists when they did, in fact, spawn naturally on their own. The programs used to balance the ecosystem were completely blown up by this fact and there were suddenly more salmon than the lake could sustain. Alewives were the original justification to introduce these fish as they could act as a predator without the mortality seen in the native (to Lake Ontario only) Atlantic salmon. Too many predators and the prey species crashed. Many studies have gone to try to understand how many natural spawning offspring are added to the system each year but the damage has been severe.

Because of this, many fisheries usually rely on a hybrid of fish species. True hybrids cannot produce fertile offspring. Because of this, the predator species are far easier to keep track of to balance the influx of an invasive prey species. In smaller systems like small lakes, you will see the introduction of Tiger Musky rather than pure bred Muskellunge for that reason.

The other “problem” is that this model generated a multi billion dollar fishing industry. Most predators being introduced are used to correct or mitigate an imbalance then weened away as the problem partially corrects itself. Due to the financial impact of the industry, the model is now being used to perpetuate into the future. Hope this helped.