Researchers have identified a novel virus found in the brains of Eel River salmon from last year’s strenuous run, but the find is not generating any concerns for fish health this year.
U.C. Davis Associate Professor of medicine and epidemiology Esteban Soto Martinez said there is much they don’t know about the virus, but said that it was likely the “perfect storm” of poor river conditions such as drought, warm water, algae, and parasites that allowed it to infect the salmon. Soto Martinez said some viruses are “opportunistic” in this way.
“It is not only the virus that was affecting the fish, but a number of different conditions,” Soto Martinez said.
Replicating these harsh conditions in his lab has been difficult, but Soto said they have found through tests the virus can infect the brains and posterior kidneys of laboratory Chinook salmon.
NOVEL, BUT NOT A CONCERN
What tipped off researchers to the virus was monitoring efforts by the environmental nonprofit organization, the Eel River Recovery Project.
Around October 2015 when flows on the Eel River were nearing record low levels, volunteer surveyors and divers found that some Chinook salmon had gone blind and were exhibiting odd behaviors. Divers could swim right up to the salmon and touch them before the fish would swim away. Other fish seemed lethargic.
After being notified of these behaviors, the California Department of Fish and Wildlife decided to take some fish and have Soto Martinez test them. What they found was grisly. Flukes, a type of intestinal flatworm, had been burrowing into the eyes of the salmon and reproducing.
Of the 10,000 to 15,000 estimated Chinook salmon in last year’s run, Eel River Recovery Project Executive Director Patrick Higgins said that about 20 percent are estimated to have been infected by the eye fluke.
But they also found the brains of the fish had lesions and were hemorrhaging, which Soto Martinez later found to be caused by the virus. However, the virus itself has not proven to be fatal to both the wild and laboratory-tested fish, Higgins and Soto Martinez said.
“It did not appear to be the principal cause of the disease or mortality,” Higgins said. “The virus is of interest, but I don’t think it was a threat in and of itself unless we have extremely challenged health of the animals, which was primarily caused by the fluke.”
Department of Fish and Wildlife Fish Health Coordinator Mark Adkison of the Rancho Cordova-based Fish Health Laboratory holds a similar view.
“If the fish hadn’t gotten affected by the fluke, I’m not sure we would have even seen these fish and found the virus,” Adkison said. “It’s not a virus we’ve seen before. I’m not sure if we’ll see it again. It might cause problems in the future. So far none of the data that Dr. Soto has generated gives me too much concern at this point.”
Soto Martinez said there is a further need to study how the virus infects the salmon, especially as this find was rare.
“There are a number of viruses that can affect wild fish, and with new diagnostic methods we are trying to understand their distribution and conditions in which they cause diseases,” he said. “Just because a virus is present, it doesn’t automatically mean they are the cause of diseases.”
‘MUCH IMPROVED’ YEAR
Higgins and other researchers have found no signs of the fluke or virus in this year’s salmon run, which has been taking advantage of the early rains to make their way up to their spawning grounds throughout the 3,600-square-mile basin. Compared with last October when the river was nearing record low flow levels, the county experienced a near record amount of rainfall this October. On Halloween, Higgins said one gauge on the river recorded the river’s flow at 40,000 cubic feet per second when it normally flows around 175 cubic feet per second.
“The fish have a tremendous amount of water to ride and a tremendous amount of water to hide,” he said. “… It looks like a much improved year for fish health.”
Due to the high flows, Higgins said their volunteers have been using drones to count the fish instead of their normal dive counts. Higgins estimates that anywhere between 1,500 to 3,000 salmon have entered the river in this first wave of fish, with some having already made it down to the Van Arsdale Reservoir in Mendocino County. Whether or not the run will be similar to last year’s near-average amount or mirror 2012’s large run of between 30,000 to 50,000 salmon will not be known until later in the winter, Higgins said.
The Eel River Recovery Project is set to hold its five-year anniversary celebration on Sunday at the Monday Club in Fortuna located at 610 Main Street. Doors will open at 4:30 p.m. with seafood dinner being served at 6 p.m. followed by presentations of the project’s work. There is no admission charge, but attendees are encouraged by the project to become a member of the project for $25 per individual or $35 for a family. More information can be found online at www.EelRiverRecovery.org or by contacting Higgins at 707-223-7200.
Article by: Will Houston
Published November 4, 2016 by The Eureka Times Standard
Read original here.