OLYMPIA – Nearly all of the 3.5 million fall chinook salmon smolts scheduled for release from the Ringold Springs Hatchery on the upper Columbia River have died – most likely of botulism poisoning, the Washington Department of Fish and Wildlife (WDFW) announced today.
Those five-month-old fish represent about 20 percent of the chinook salmon smolts scheduled for release by WDFW hatcheries in the upper Columbia River this year, said John Kerwin, WDFW hatcheries division manager.
Kerwin said the three-inch-long smolts began dying shortly after they were transported in mid-May from Oregon’s Bonneville Hatchery to the Ringold facility, located 20 miles upriver from Pasco.
“We started testing for routine viruses and bacterial infections right away and the results all came back negative,” Kerwin said. “But the smolts were dying in increasing numbers so we knew we had to keep looking.”
No such problems have been reported at the Bonneville Hatchery, which rears the fish for release at the Ringold facility under a standing agreement with the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers.
A possible explanation for the fish kill came late last week, when WDFW received word that two of 10 samples sent to the Cornell University Veterinary College tested positive for the bacteria that produce botulism, a naturally occurring toxin responsible for occasional fish kills at hatcheries in Washington and other states.
“We’re still waiting for the results from other tests, but botulism appears to be the most likely suspect,” Kerwin said.
Because botulism can be toxic to humans as well as fish, Kerwin contacted the Washington Department of Health about the findings. Dr. Mira Leslie, an epidemiologist for the state health agency, sees little risk to humans from the smolts at the hatchery.
“Botulism in humans is a rare disease,” Leslie said. “Unless someone were to eat these small fish raw, I really don't see any human health risk.”
Kerwin said the dead fish will be recovered, covered in lime and buried on the hatchery grounds to kill any botulism toxins.
The smolts – originally scheduled for release next week – were expected to return as adult salmon in 2008 and 2009.
“At this point, it appears we’ve lost them all,” Kerwin said. “We’ll have a better idea once we finish draining the rearing pond.”
Once the rearing pond has dried out, it will also be treated with lime, Kerwin said.
The last occurrence of botulism poisoning at the Ringold hatchery was in 1999 – then with spring chinook smolts, said Steve Roberts, WDFW fish health specialist. The toxin also has caused fish kills in Washington and in other states on a sporadic basis, he said.
“The bacteria that produce the toxin require certain conditions to become active,” Roberts said. “It can only live in an oxygen-deprived environment and is often found in decaying matter. Sometimes, especially during warm weather, fish will die from some other illness and that can set it off.”
The earthen floor and sides of the rearing pond at the Ringold facility could be the source of the botulism toxin, Kerwin said. In addition, the shear size of the pond makes it especially difficult to monitor the condition of the fish, he said. Covering nine acres with depths of up to 12 feet, the earthen pond is the largest of its kind in the state.
“It’s not an ideal situation for rearing fish,” Kerwin said. “In past years we’ve requested federal funding to divide the holding pond up into more manageable units, but we’ve never been successful.”
The Ringold Springs Hatchery was built in the early 1950s by the federal government, which still provides funding to operate the facility as mitigation for hydroelectric dams on the lower Columbia River.