ARCATA -- Fish health experts convened Thursday to sort out what's known -- and what isn't known -- about two parasites plaguing salmon on the lower Klamath River. The unusual parasites can be found in the majority of young chinook salmon in the lower river, and can cause fatal diseases that have claimed tens of thousand of fish in recent years. But the parasites' complicated life history and effects, as well as water quality problems and ocean conditions, make deciphering their role in struggling salmon runs tricky. ”These fish have evolved with this parasite,” said Scott Foott with the U.S. Fish and Wildlife California-Nevada Fish Health Center, “it's just a question of how much of it is out there.” The group met at Humboldt State University for the second year to share research and pave the way for future studies and coordination between agencies, tribes and scientists. The parasites Ceratomyxa shasta and Parvicapsula minibicornis can damage the intestines and kidneys of young chinook migrating out of the river. But while they have been killing little fish for years, outbreak go almost unnoticed, unlike the obvious and widely covered demise of up to 68,000 adult fish in the fall of 2002. C. shasta and P. minibicornis can be found in many of the major river systems in the West. They appear to have become significantly more abundant in the Klamath in the last decade, Foott said, but they are not being found in the river's tributaries. Both parasites have an alternate host in a 2- to 3-millimeter-long polychaete worm, which could offer a clue on how to manage the diseases they cause, said Jerri Bartholomew, a researcher with Oregon State University. The worms are especially abundant in certain parts of the river. But what matters more is how many of the worms in a specific spot are infected with the parasites, Bartholomew said. For example, near Keno Dam, the worms are prolific, but uninfected, and so are most of the fish in those areas. But in the lower river, the worms are fewer but more infected. So are nearly all the fish there, many of which then die. ”There's something very different going on in the lower river from the upper river,” Bartholomew said. Two things appear clear. One, the longer fish are exposed to water with parasite spores, the less resistance they have to them. Two, the higher the water temperature, the more abundant the parasites. Bartholomew said the effects of flow -- low flows were a key factor in the 2002 fish kill -- are difficult to separate from the effects of temperature. However, lower flows during fish migration may increase exposure, concentrate infection into certain areas and increase the worm host's distribution and abundance, she said. In 2004 and 2005, Ken Nichols and others with Fish and Wildlife examined different reaches on the river. In 2005, nearly 90 percent of the fish sampled were infected with one of the parasites -- 65 percent of them severely. Most often, they were also infested with the other parasite. ”The combination of two parasites is not helping,” Nichols said. Key to understanding the relationships between salmon, the parasites and the polychaete worm is being able to detect its presence quickly. A new method created by Bartholomew and co-worker Sasha Hallett can detect even the smallest fraction of a parasite spore in a water sample, according to a summary provided at the workshop. |
||||||||||||||
