It's not just the acute toxic effects that are concerning though. Returning spawners will actually turn around and head back downstream when faced with sub-lethal levels of toxic metals. Atlantic salmon in the Miramichi were shown to avoid water when the concentration of copper and zinc from a mine discharge was just 35% of the LD50 concentration. Less than half would reverse and swim back upstream to the best spawning areas after that event. That means they are choosing to spawn in areas less than ideal, which means lowered survival for the next generation. This year's sockeye run is of the 2010 generation, which came from the largest returning generation of sockeye in over 100 years, so it's important that this cycle doesn't get knocked down.
A second consideration is the amount of solids that will settle. If the fish are returning downstream to less than ideal conditions, and some of this heavier material settles in the lower flows downstream, then that is even further pressure on the hatching fry. It will also mean lowered dissolved oxygen in the substrate where the fry seek refuge. By that time the pulse of high pH water will have moved past, and the river will have become more acidic. Fry, also are less hardy than the adults, so the lethal concentrations, and those that begin to cause congenital defects, is much lower.
Not a good fate for fish when stuff like this happens. It's way too early to tell though. Like I said, hope for the best!
A second consideration is the amount of solids that will settle. If the fish are returning downstream to less than ideal conditions, and some of this heavier material settles in the lower flows downstream, then that is even further pressure on the hatching fry. It will also mean lowered dissolved oxygen in the substrate where the fry seek refuge. By that time the pulse of high pH water will have moved past, and the river will have become more acidic. Fry, also are less hardy than the adults, so the lethal concentrations, and those that begin to cause congenital defects, is much lower.
Not a good fate for fish when stuff like this happens. It's way too early to tell though. Like I said, hope for the best!
Jon Woodward @ctv_jon
