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Ecology and salmon related articles

Barging Fish In May
Still Beats Swimming

by Bill Rudolph
NW Fishletter, December 13, 2012

The latest fish survival results from NOAA Fisheries still support the feds' view that barging fish from lower Snake dams in May would be a good thing compared to leaving them in the river, despite the opinion of former U.S. District Judge James Redden, who oversaw the BiOp proceedings.

Redden issued court orders in 2005 and 2006 boosting spill levels from mandated-BiOp levels, bolstered by arguments from BiOp plaintiffs. His order reduced adult returns of both ESA-listed spring chinook and steelhead, because the higher level of spill meant fewer numbers of juvenile fish have been collected for transport.

The results were given in typical low-key presentations at the Corps of Engineers' annual research review, held in Portland two weeks ago.

The newest analysis estimates the benefits of transport compared to all bypassed fish, including fish not detected at Snake River dams. Non-detected fish pass dams via either spillways or turbines where no PIT-tag detection is possible. The researchers say this gives a more realistic estimate of potential benefits from transport to the run-at-large, though some critics have claimed over the years that survival of the non-detecteds should be the gold standard by which transport benefits are measured. That's because most non-detected fish use spillways to pass the dams, where survival is generally thought to be highest.

But the NOAA researchers found that was not always the case, and pointed it out in their latest results.

For the 2009 outmigration, for instance, they estimated that non-detected juvenile wild chinook, which were estimated to make up about 30 percent of the inriver run, returned at only 84 percent of the rate of bypassed wild fish.

For several years before that, the difference was only a few percent. But in 2005, the non-detecteds returned at only 44 percent of the return rate of bypassed fish. Then, in 2004, the non-detecteds returned at better than twice the rate of bypassed, detected fish.

Overall, the survival benefit of the non-detecteds over the bypassed wild chinook averaged only 6 percent between 1998 and 2009 (excluding 2001, a year of little to no spill). For non-detected hatchery chinook over the same period, which typically account for half of the inriver run, the benefits seemed higher, a return rate 23 percent higher.

For wild steelhead, the undetected component (about one-third of the inriver run) showed a 31-percent benefit, when outlier years were removed. Undetected hatchery steelhead, which make up about one-third of the inriver run, showed a 69-percent higher average survival rate than bypassed steelhead for the same period.

The data from the 2009 outmigration (with returning adults through 2012) showed that transported wild and hatchery chinook had much better smolt-to-adult return rates (SARs) than inriver migrators (non-detecteds and detecteds) from May 1 through the end of the migration season, though the adult count was low for the wild returns. The results also showed wild steelhead from the 2008 outmigration had better SARs by nearly a factor of two than inriver migrators. Hatchery steelhead SARs in 2009 beat inrivers after May 10.

According to the researchers' abstract, the lowest SAR of the season for transported groups often occurred in the group that was barged earliest. After investigating various covariates, they said no single one stood out to explain the differences in SARs during the spring time frame, but they noted that water temperature "was most strongly associated with SAR among the covariates we investigated."

The presentation showed that prior to 2006 (before the court-ordered spill regime was implemented), the estimated ratio between transported and inriver fish (detected plus non-detected) SARs almost always exceeded standards (above 1:1) for fish arriving at Lower Granite Dam on May 1 or later, the first collector dam where fish are barged from the lower Snake.

"Patterns did not change drastically in 2006-2009, but the earliest date on which T:B exceeded standards was more likely to be later in May (e.g. May 10), especially for steelhead," the presentation noted. The researchers said more years of data will be required to find out how much the changed transportation strategy has altered SARs and the survival patterns of barged and inriver migrants.

Others reported on the latest survival data to determine whether BiOp juvenile performance standards are being met at projects. At Little Goose Dam on the lower Snake, with 30-percent spill, spring chinook survival averaged above 98 percent, well above the 96-percent standard, steelhead survival averaged 99 percent, and fall chinook survival averaged 95 percent (93-percent performance standard).

At Lower Monumental Dam, with 20-29 kcfs spill in the spring (to gas cap) spring chinook survival averaged better than 98 percent, steelhead 98 percent, and fall chinook nearly 98 percent, though high flows made spill targets hard to reach. The presentation did note that dam survival was not different between high and low spring spills.

On the mainstem Columbia, where high flows also made spill targets hard to achieve, the second year of the new studies at John Day Dam with 30-percent and 40-percent spill treatments, found nearly 97 percent of juvenile spring chinook making it past the project, with better than 97 percent survival of steelhead, and 94 percent survival of young fall chinook.

At The Dalles Dam, in its third year of study, with a 40-percent summer spill target, researchers found juvenile fall chinook survival exceeded 94 percent. Earlier findings in 2010 and 2011 found that survival of spring chinook exceeded performance standards and steelhead nearly so, with better than 95 percent survival in 2010, and more than 99 percent survival in 2011. In 2010, fall chinook survival had also been pegged above 94 percent.

At Bonneville Dam, with two spill treatments (85 kcfs day, 120 kcfs night, 95 kcfs day/night), survival of juvenile fall chinook was estimated above 97 percent. Earlier studies in 2010 and 2011 estimated spring chinook survival above 95 percent, steelhead between 95 percent and 96 percent, and a study of fall chinook in 2010 found survival nearly 96 percent.

Other research found large survival differences between single-release studies compared to paired-release studies (which use control groups) for juvenile steelhead passing top-spill weirs at McNary Dam. Paired-release studies are now mandated by the hydro BiOp.

In 2012, steelhead survival was above 97 percent in the paired-release study, but only 90 percent in the single-release study. Spring chinook survival was better than 97 percent in the paired-release study, but only 93 percent in the single release.

Another study at McNary Dam to measure survival through the juvenile bypass system that was extended to mid-channel in 2012 to reduce predation, found single-release studies conducted earlier this year estimated steelhead survival at about 94 percent, while the paired-release version estimated it at 100 percent.

Spring chinook survival was pegged at 89 percent in the single-release study, but close to 94 percent in the paired-release study, and fall chinook survival was around 95 percent in the single-release version, but actually estimated slightly above 100 percent in the paired-release version.

Overall, paired-release studies at McNary have found that spring chinook and steelhead reached the 96-percent BiOp performance standard for dam passage, and fall chinook more than 4 percent above the 93-percent standard for that species, when all routes of passage, weirs, spillway bypass system and turbines, are considered.

Related Pages:
Latest NMFS Analysis Backs Up Late Spring Barging Strategy by Bill Rudolph, NW Fishletter, 12/14/11

Bill Rudolph
Barging Fish In May Still Beats Swimming
NW Fishletter, December 13, 2012

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