Bonaro-
As often is the case with fish issues the devil is in the details.

There is little disagreement in the literature regarding impacts from dredge type activities that eggs and the young fry before emerging from the gravel are at risk during dredging activities. While the mortality of the egg/fry will vary depending on the situation some (in some cases 100%) will die.

The rub is that here in the PNW and north Puget Sound especially with multiple species with diverse spawning times there can be eggs in the gravel for most of the year (and in some cases all year round).

Just one example would be in the Skagit basin where steelhead (and resident rainbows) spawn from early March into July. Spring Chinook begin spawning in August and September, the other races of Chinook and salmon species can be found spawning from September into March.
With the fry from the spawning steelhead still coming out of the gravel into September it should be clear that there is potential to kill fish or their eggs year-round.

The TU project you referenced in previous post was in Colorado which to my knowledge have not salmon (except kokanee in few isolated areas) so the time window for work would be much wider than some areas here in Washington. As I said the devil is in the details.

curt