LEWISTON — Federal fish managers say they opted to kill tens of thousands of juvenile steelhead after finding a potentially deadly virus in two holding ponds at the Dworshak National Fish Hatchery.
Hatchery manager Larry Peltz says the fish were killed Tuesday to reduce the threat of the viral disease called Infectious Haematopoietic Necrosis, or IHN, spreading to other hatchery holding ponds at the facility.
INH infects salmon and trout and can be fatal. But the virus can also be carried and passed on by survivors, posing a threat not just to other holding ponds but bigger water bodies.
“When fish break with IHN you have a source of the virus sitting right there,” Peltz told the Lewiston Tribune. “If you leave them there, the virus is there and the potential for the virus to spread exists.”
The kill is the second in recent weeks of juvenile fish at hatcheries that are helping to bolster Idaho’s populations of fish.
Last month, about 40,000 sockeye salmon were killed at an Oregon hatchery. Officials blamed a damaged valve at the Oxbow Fish Hatchery, at Cascade Locks, Ore., for wiping out about a quarter of the juveniles destined for mountain lakes in central Idaho next year.
Despite Tuesday’s loss at the Dworshak hatchery, located near Orofino, Peltz says the facility is on pace to meet its goal of releasing 2.1 million steelhead smolts next spring.
The outbreak of INH is the latest to plague the hatchery. In recent years, the hatchery has reported several infections and higher rates of fish mortality.
The disease is carried by adult salmon and steelhead and enters the hatchery when water is pumped in from the North Fork of the Clearwater River below Dworshak Dam.
Most of the hatchery’s water comes from the river and a smaller portion from Dworshak Reservoir, which has very low rates of IHN. To help combat outbreaks, hatchery officials have been working to keep juvenile fish in reservoir water for as long as possible.
The theory holds that if fish managers wait longer to expose fish to river water and IHN, the fish have a chance to grow stronger and are better able to fight off the disease.