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Restoring Upper Willamette River Basin Salmon Runs Challenged By Soaring ‘Pre-spawn Mortality’
Posted on Friday, February 04, 2011 (PST)

Fishery managers and researchers face a number of troublesome questions before pursuing their goal of reintroducing chinook salmon, and building viable naturally spawning populations, to historic and relatively pristine habitats in the upper Willamette River basin that are now blocked by impassable dams.

 

Perhaps the toughest scientific question is how recovery can be achieved given soaring “prespawn mortality” that has been witnessed when spawners are trapped and transported around the dams and released to continue their journey. PSM occurs after the fish have made the long trip home from the ocean and have reached their spawning tributary.

 

While the numbers vary from river to river and from year to year, as many as 90 percent of those transported fish have died before they finish their mission, according to recent research.

 

Those researchers and others gathered last week to share the results of biological studies undertaken over the past year to address questions about fish behavior, life history characteristics, habitat use, survival, and condition as they migrate through the Willamette mainstem and its tributaries. The 2010 Willamette Basin Fisheries Science Review, which was sponsored by the U.S. Army Corps of Engineers, took place Jan. 24-26 at Spirit Mountain Casino near Grand Ronde, Ore.

 

Much of the research is expected to advise implementation of two 15-year ESA biological opinions that were issued on July 11, 2008, after eight years of federal “consultation.” The BiOps evaluate the impacts on listed stocks caused by the 13 Willamette Project dams and reservoirs, maintenance of 42 miles of revetments, and operation of the Hatchery Mitigation Program. They recommend actions necessary to counter those negative impacts.

 

The federal agencies involved include the Corps, the Bonneville Power Administration, the U.S. Bureau of Reclamation, the U.S. Fish and Wildlife Service and NOAA Fisheries Service. The Corps operates the dams, BPA markets power generated in the system, the Bureau administers water rights and NOAA Fisheries and the USFWS, which issued the BiOps, are charged with protecting listed stocks. Those species include Upper Willamette spring chinook salmon and winter steelhead, bull trout and Oregon chub.

 

The BiOps call for the development of up and downstream fish passage at three federal dams, the construction of a temperature control structure at another dam, the screening of irrigation diversions, improved dam operations, improved hatchery practices and facilities and habitat improvements.

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Annual research reviews are used to share information from these efforts. The review includes fisheries research in the basin for both Corps-funded work and research by other entities.

 

The Corps is most interested in information to facilitate decisions on the operation and configuration of its 13 dams that constitute the Willamette Valley Project system, and on strategies to mitigate for the dams impact on salmon and steelhead populations.

 

Last week’s 2 ½-day session included presentations on juvenile salmonid dam passage studies, salmonid life history studies, lamprey, bull trout and chub, adult salmon and hatchery management, water quality and in-stream flow and habitat.

 

Researchers lay the blame for PSM on a variety of interacting environmental factors (particularly water temperature), fish condition and disease load, and energetic status. The higher the temperature in a natal stream, the higher the mortality. Likewise injured and/or diseased fish are less likely to spawn.

 

Injuries can occur when the fish are trapped and kept in holding tanks.

 

Current PSM rates could prevent recovery despite plans to improve downstream passage past Cougar, Lookout Point and Detroit dams for any juvenile fish that might emerge from upstream spawning, according to the Corps’ David Griffith.

 

A number of the suspected contributors to high PSM can be addressed, such as improvements to collection facilities and release sites to reduce physical injuries and fine-tuning dam operational and transportation protocols. Efforts too can be taken to reduce fish densities below traps (higher densities seem to result in higher PSM after the chinook are trapped, transported and released) by increasing harvests and/or reducing hatchery output.

 

And research and planning is under way to improve water quality – temperature and flows – through operational and structural means.

 

“It’s not a unique thing to the upper system,” Oregon State University’s Carl Schreck said. High prespawning mortality is in other tributaries in the upper Willamette as well as in the studied streams such as Fall Creek and the Middle Fork of the Willamette.

“Maybe what’s going on in these areas is the consequence of what goes on below there,” said Schreck, who presented results from research titled “Pathological Changes Associated with Prespawning Mortality in Chinook Salmon in the Willamette River and Management Options.”

 

The research indicated the intensity of infections with pathogens and parasites in chinook is generally more intense at Dexter Dam on the Middle Fork than it is far downstream at Willamette Falls on the lower Willamette.

 

“As in the prior year, we identified massive infections and severe lesions in fish that died prior to spawning. It appears that the fish are becoming infected with some of the parasites in the river above Willamette Falls, as judged by lack of presence of parasites in fish from below that area,” according to the study abstract. “Examination of fish from the falls and held in pathogen free water would confirm this.”

 

“In addition, conditions in the upper river, perhaps elevated temperature, appear responsible for some heavy parasite burdens in fish maturing in the upper river system; this contention is based on the fact that fish that matured in cool, pathogen free water at the FPGL did not have such infections, and there is a time effect.”

 

As a part of the research some fish trapped at Dexter and Fall Creek were brought to the Fish Performance and Genetics Laboratory at OSU and allowed to mature in a cool, pathogen free facility before being released.

 

“Parasite associated mortality is probably something driving prespawning mortality” along with temperature and other environmental variables, Schreck said.

 

“A viable management option is suggested by our findings,” the study abstract says. “It appears that holding fish in cool, pathogen free water for much of their maturation prior to outplanting could enhance survival to spawning. However, to optimize these effects we suggest that fish from earlier parts of the run could be used, as their survival to spawning (90 percent) was considerably higher than those collected later (70 percent). As judged from our small sample size, earlier and later transported fish still spawned at the same time, therefore genetic consequences of such a tactic could be minimal.”

 

Other findings, such as those presented by the University of Idaho’s Chris Caudill show that earlier arriving fish survive to spawn at a better rate than those that arrive later in the season, due perhaps to higher initial energy stores to call on as they idle through the summer before spawning in late September or October.

 

A total of 192 chinook were collected at the Dexter trap and were outplanted upstream the North Fork Middle Fork last year as part of research led by Caudill, “Migration Behavior and Spawning Success in Spring Chinook Salmon in Fall Creek and the North Fork Middle Fork Willamette River: Relationships Among Fate, Fish Condition and Environmental Factors: 2008-2010.”

 

“To assess the effects of holding fish on prespawn mortality an additional 100 Chinook salmon were sampled, held at Willamette Hatchery in Oakridge, Oregon, and then outplanted to the NFMF prior to spawning,” the study abstract says.

 

“Prespawn mortality of immediate NFMF outplants was estimated to be 57.9 percent. In contrast, prespawn mortality after outplanting hatchery-held fish was 13.3 percent (note: an additional seven mortalities occurred at the hatchery). Even accounting for mortality during holding, fish held at the hatchery exhibited an increase in survival during the 2010 season compared to immediate outplanted adults. The higher survival may have been related to the use of antibiotics for hatchery held fish and/or cooler holding temperatures."

 

Griffith said long-term holding of wild fish destined for above dams would not be a preferred alternative but may be necessary. The BiOp calls for improvements or replacements of fish traps at Minto on the North Santiam, Foster on the South Santiam, Dexter and Fall Creek, which could potentially include holding facilities.

 

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