First, the best hatchery is the river system itself, but there are circumstances where hatcheries are needed to try to help restore populations.
Aquaculture fish have been reared and kept domesticated for several generations now. In the early phases of our studies on the Magaguadavic River in the early 1990s, we believed the survival was quite good. When fish escaped they would get into the river system. We saw high numbers of fish getting into the river system, compared to what we thought had been escaping at the time.
Fast forward another 10 to 15 years, and the survival of fish, when they escape from the net pens, is very low. We estimate that maybe 0.1% or 0.2% of those fish that escape from the net pens make it into the wild streams. Going back to what I said earlier about being so domesticated, if those fish were to interbreed with the wild fish in the stream, studies have shown that it can be quite detrimental to the fitness of the offspring.
Some of these streams--we're monitoring the rivers--have as few as six or 10 wild fish going into the rivers, so it only takes one or two escapees into those river systems to spawn with the wild fish to effectively reduce the fitness, meaning that in subsequent generations it will be much harder for the fish to survive in the future.