Brood Stock Deaths Mounting At Sawtooth Hatchery

Chinook salmon held for spawning at the Sawtooth Fish Hatchery near Stanley are dying in unusually high numbers.

So far 150 of the 320 adults held at the hatchery have died.
The salmon being held as brood stock are dying primarily from a common freshwater fish parasite, Ichthyophthirius multifilis, known as "ICH" or "white spot."

Because of this year's low run of Chinook salmon to the Sawtooth hatchery, the ICH breakout means that the smolt production target for this hatchery will not be met. The hatchery program plays an important role in preserving future fishery and recovery opportunities.

The hatchery is operated by Idaho Department of Fish and Game, and the spring Chinook are part of the Snake River Chinook salmon population listed under the federal Endangered Species Act.

The parasite, once established, produces a white spot on the fish and can be especially deadly when there are severe infections on the gills of the fish.

As the water temperature approaches 72 degrees, the life cycle is completed in shorter time periods and the parasite becomes more prevalent.

Until they spawn, spring Chinook are held in large ponds at the hatchery supplied with water from the Salmon River. Recent hot weather has pushed water temperatures in the ponds into the low 70s.

But the fish in the hatchery are not the only component of this population. More than 300 hatchery and naturally produced Chinook salmon have also been allowed to pass upstream of the hatchery into the headwaters of the Salmon River to spawn naturally and for supplementation research.

Hatchery officials typically expect that a few adult salmon will die each year before spawning, but it is usually less than 10 percent.

Sawtooth hatchery staff members noticed the increased levels of pre-spawning mortality caused by ICH in late July 24 and began treating the parasite aggressively.

Treatment will continue until either the parasitic infection is reduced or water temperatures go down, which should slow the infection rate and reduce further mortality.

Confounding factors, such as turbid runoff from last year's forest fires upstream of the hatchery and an unusual abundance of naturally occurring sea lice on the gills of the adults, complicated department efforts to reduce the mortality.

If water temperatures remain high, more fish may die, even with treatment. The department is using all of its technical resources in fishery disease management to slow the infection and reduce adverse effects on the Chinook program.