After Klamath River flushes, C. shasta spores spike, surprising scientists

She reported the preliminary results to the Klamath Irrigation District board members last week. Board members were taken by surprise, as were the scientists on the ground who are studying the river.

However, it is not that the flushing flows are not working.

“One potential preliminary hypothesis is that adult salmon were infected last year when they migrated up the river to spawn,” Skinner told the KID board.

“When they died after spawning, they released spores that were taken up by polychaete worms (infection rates in polychaetes prior the flushing flow were notably high this year). Polychaetes that survived the flushing flow then released spores this spring that infected juvenile salmon. The spores can and do result in salmon mortality.”

In the most recent sample, 83 percent of sampled fish were infected with C. Shasta, Skinner said. Of that 83 percent, 13 percent had an infection that could likely lead to mortality.

As one may recall, Reclamation was under court order in 2017 to flush the river with a ballpark of 50,000 acre feet of water to dislodge the worms that host the spores. (The spores in turn then infect juvenile salmon, especially the ones being release from the Iron Gate hatchery.)

Now, there is a new 2019 Biological Opinion in effect as of April 1 that guides the Bureau of Reclamation on its water allocation, so the court order is moot.

First a little biology

According to Sascha Hallett, microbiology senior research associate at Oregon State University, the purpose of the flushing flows is to mobilize sediment and reduce polychaete worm (invertebrate host of Ceratonova shasta) populations, thereby reducing the numbers of hosts available to produce the infectious stage for salmonids (salmon and trout).

“Polychaete sampling by Julie Alexander of OSU — before and after spring flows — indicate a reduction in worm numbers following the increased flow. However, the determination of whether the number of infected worms also decreased is still in progress (sample processing is underway). Reductions in both infected and overall populations have been observed in previous years following high spring flows,” Hallett told the Herald and News.

High parasite levels have been observed in previous years characterized by low precipitation (low flows) and warm temperatures. Therefore, this year because of the high precipitation, flow events, cool winter water temperature and decrease in polychaetes, we were anticipating a low parasite year, and if temperature remained low, a low disease year, she said.

Parasite levels in the river usually increase with increasing water temperature in spring.

“Indeed, this is what we observed this year — waterborne parasite was not detected until mid-spring, which is typical of a low-moderate disease year. However, once levels began to increase they did so surprisingly quickly — by more than an order of magnitude from one week to the next,” Hallett said.

Although the waterborne parasite levels are unexpectedly high post-flow this year, and of concern, these levels might have been even higher had the flows not occurred, Hallett noted.

“So it is too early to know whether the flows achieved all components of their goal,” Hallett said.

It is important to be mindful that high parasite abundance alone does not necessarily translate to disease and population-level impacts on salmon – river water temperature and length of exposure (i.e. total parasite dose) are also contributing factors.

From Reclamation’s perspective

“The flushing flow last month was done under the 2019 Biological Opinions,” said Laura Williams, public relations for Reclamation.

“The total amount of water used specifically for the flow is not important under the new BiOp. For this flow especially, the total water used is not important since it was done as part of flood control operations. The water would have gone down river because it was necessary to release it to keep the levies surrounding Upper Klamath Lake from breaching” she said.

The actually flushing flow numbers required are 6,030 cubic feet per second for 72 hours. However, because it all happened as a result of required flood control operations, much higher flows happened to keep people safe, Williams noted.