Black Spot Disease in the Lower Deschutes

For anyone who has fished the lower Deschutes River this year, it is not news that many of the fish being caught have Black Spot Disease (BSD). How many fish? We’ve received reports of as many as 100% of 30 fish caught over a three-day trip between Trout Creek and Harpham Flat. Most reports are that 60 to 80% of landed trout have obvious evidence of BSD.

Lower Deschutes River bull trout showing obvious Black Spot Disease. Photo courtesy of Nick Wheeler.

We, along with several of our supporters, have contacted representatives of the Oregon Department of Fish and Wildlife about this issue, and have been told there is nothing to be alarmed about. One of our supporters received an email from ODFW that included the following:

“ODFW has done some research on the effects of blackspot [sic] on spring chinook [sic] smolts in the John Day River and found that the parasite had no adverse effects on condition or survival, even fish that were severely infected performed the same as uninfected fish. Our pathologists also have stated that blackspot [sic] is not categorized as a disease, meaning that it does not appear to effect the host. It is also important to note that blackspot [sic] is very cyclical, and most often comes and goes through time.”

We’ve not seen any research reports from ODFW regarding BSD, although it’s not unusual for these reports to not be advertised or be made readily available. What is unusual is that anglers who fish the bodies of water mentioned by ODFW do not report seeing BSD. This is not to say that BSD isn’t present on the John Day and other rivers, but it’s clearly not present right now to the same extent as in the lower Deschutes.

According to the statement from ODFW, BSD “is not categorized as a disease.” This is a curious claim. Why is it called Black Spot Disease? In all of the scientific literature that we searched, it is always referred to as a disease. This is because infection with BSD results in both systemic inflammation and tissue changes in fish. Inflammation is evidenced by increased cortisol (a hormone associated with stress and inflammation) levels. The skin and scale changes seen on fish with BSD are not caused by trauma. So we have a transmissible infective organism causing inflammation and tissue changes. That meets the definition of a disease.

The fish ODFW representatives have observed with BSD are noted to be in good condition. Yes they are, when they are caught. But no one is performing long-term observation to see what the consequences of chronic infection might be. We are now in the third year of BSD being observed in lower Deschutes River fish, so it’s obvious that more fish are being infected for longer periods of time. None of the studies on BSD to date look at longer-term infections, so those consequences are unknown.

What is known is that fish do die of BSD. According to reports, once fish are infected in the eyes or mouth, survival is limited. And fish with high parasite loads tend to be of lower weight.

The ventral surface of a redband trout with Black Spot disease, caught in the lower Deschutes River in late April 2017. Photo by Jamey Mitchell.

Black spot disease is caused by a flatworm (trematode) parasite known in the scientific community as Uvulifer ambloplitis, and also known as “neascus.” This parasite has a complicated life cycle that starts with eggs in water, which hatch and become juveniles known as miracidia, which in turn infect aquatic snails.  In snails this form of the parasite matures into the next life form, known as cercariae.  Cercariae are shed by the snails and become free swimmers, which attach to fish.  Once the cercariae have attached to the flesh of a fish, the fish develops an immune response that causes the dark spot.

Fish-eating birds are the next host, which become infected when they ingest infected fish.  The cercariae develop into adult flatworms, which means that fish-eating birds are internally infected with the parasite.  The parasite then produces eggs, which are shed in feces by fish-eating birds, and deposited in water where the life cycle is reinitiated.

This summer, many have observed decreases in fish-eating birds in the lowest forty miles of the Deschutes. Kingfishers are rarely seen now in that reach of river (they were previously seen in pairs occupying nearly every reach of river), and merganser populations in the lower forty miles have declined. Are these birds becoming infected with neascus and dying? Or is something else going on? Unfortunately, no one seems to be investigating this phenomenon.

Increases in BSD are associated with increased water temperature and increased aquatic snail populations—both conditions that Selective Water Withdrawal Tower operations have created in the lower Deschutes River. Further, research has demonstrated that rather than being “cyclic,” BSD is linked to sustained elevated water temperatures and algae growth.

The likely solution to reducing BSD is a return to cooler water temperatures and less nutrient loading in the lower Deschutes River. This would require that the SWW tower draw more water from the bottom of Lake Billy Chinook before discharging downstream.

Sources

Schaaf, Cody J, Suzanne J. Kelson, Sébastien C. Nussle, & Stephanie Carlson . Black spot infection in juvenile steelhead trout increases with stream temperature in northern California. Environmental Biology of Fish,; April, 2017.

McAllister, CT, R. Tumlison, H.W. Robison, and S.E. Trauth. An Initial Survey on Black-Spot Disease (Digenea: Strigeoidea: Diplostomidae) in Select Arkansas Fishes. Journal of the Arkansas Academy of Science, Vol. 67, 2013

Schaaf, Cody J. Environmental Factors in Trematode Parasite Dynamics: Water Temperature, Snail Density and Black Spot Disease Parasitism in California Steelhead (Oncorhynchus mykiss). Submitted to University of California Berkley for Masters Thesis, May, 2015.


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Oregon Department of Fish and Wildlife Establishes No-Limit Bass Fishery on the Lower Deschutes River

On Friday, August 4, 2017, the Oregon Fish and Wildlife Commission voted to make the bass fishery in the lower Deschutes River a “no bag limit” fishery, beginning January 1, 2018.

A smallmouth bass caught last week on the lower Deschutes River.

This is a positive step toward dealing with the bass invasion of the past few years. It is also an acknowledgement that we have a problem in the lower Deschutes River. As we’ve noted in previous blogs, bass have been infrequently reported in the lower Deschutes River, in very small numbers, for many years. However, in the past two years the numbers of reported bass have grown significantly, with some anglers this year reporting catches of up to 20 bass per day below Macks Canyon.

These omnivorous and voracious predators feed on a mix of food types including juvenile fish (trout, steelhead, Chinook, shiners, etc.), crawdads, and aquatic insects. As their numbers increase, they pose an increasing threat to the ecology of the lower river.

Unlike in other fisheries where bass have been artificially introduced by well intended, but ill-advised, amateur biologists, the bass in the lower Deschutes River appear instead to have moved up from the Columbia River. This has happened because, remarkably, the lower Deschutes River is now warmer in the spring than the Columbia River. This is due to current selective water withdrawal operations at the tower above Round Butte Dam. During springtime, 100% surface water withdrawal is used to attract juvenile fish to the fish collection facility at Round Butte Dam. This surface water is many degrees warmer than water at the bottom of the reservoir, which was the source of water for dam operations prior to 2010.

The warmer water in the lower Deschutes River attracts bass and allows them to become more active earlier in the year. This gives them more time to feed before the next winter, and an earlier start on spawning.

DRA Board member Steve Pribyl with a smallmouth bass caught last summer.

Perhaps the saddest comment on the new bag limit is that most anglers are releasing the bass they catch in the lower Deschutes, in order to have something to catch in the future as this treasured river continues to change so rapidly. However, we would encourage all anglers to remove these fish from the water. Do not dispose of them on the bank, as that is a violation of rules regarding wasting of game fish.

The need for this change in fisheries management is another unanticipated and unintended consequence of SWW tower operations. And another sign that it’s time to reconsider how the tower is operated, along with current strategies for reintroducing fish above the Pelton-Round Butte Project.


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You Don’t Need a Weatherman…

By Greg McMillan

To paraphrase Bob Dylan’s song “Subterranean Homesick Blues,” you don’t need a weatherman to know it’s suddenly become hot outside.  And the lower Deschutes River is warming with the weather.  As shown in this graph from the temperature gauge at Moody, the river hit nearly 72 degrees F. on Sunday, June 7.  More hot weather is in the forecast.

Lower Deschutes water temperature at Moody, near the confluence of the Deschutes and Columbia Rivers. Courtesy USGS Moody Streamgage online data.

Lower Deschutes water temperature at Moody, near the confluence of the Deschutes and Columbia Rivers. Courtesy USGS Moody Streamgage online data.

Dylan’s actual line was, “You don’t need a weatherman to know which way the wind blows.”  And we know which way the wind is blowing regarding temperature management at the Pelton-Round Butte Dam Complex using the Selective Water Withdrawal (SWW) Tower.

The dam operators have been using a temperature management model that seeks to “eliminate the thermal presence of the dams.”  Combining surface (warm) and bottom (cool) water withdrawal in the SWW Tower is supposed to do this.

Combining the temperatures of the Lake Billy Chinook tributaries and the air temperature at Redmond Airport and plugging them into a statistical equation determines the temperature goal for water discharged from the dam complex.  The warmer it gets, the warmer the discharge from the dams should be according to this model.

This is analogous to turning up your home’s furnace during hot weather, instead of turning on the air conditioner.  The dam operators, according to their Water Quality Management and Monitoring Plan (WQMMP) are to further warm the river when it’s already warming due to weather conditions.  This makes no sense from a biological perspective.  When is it ever better to warm a salmon-trout-steelhead river?

Last year the dam operators lowered the temperature of the lower Deschutes by increasing bottom water draw from 15% to 45% on July 18 and 19.  The Deschutes River Alliance hopes and advocates for the dam operators to again provide cooler water for the lower river during the hot months ahead.  Only this year, do it sooner.

4 pm temperature in Bend, June 8, 2015

4 pm temperature in Bend, June 8, 2015. Photo by Greg McMillan.

Lower Deschutes River. Photo by Brian O'Keefe.

Lower Deschutes River. Photo by Brian O’Keefe.