The time is not yet ripe to choose a spill-smolt transportation regime for Columbia and Snake river hydro projects that best promotes life cycle survival of salmon, steelhead and lamprey, according to a new report by the Independent Scientific Advisory Board.

"Spreading the risk" between the in-river migrations of juvenile fish and transporting them through the system aboard barges has been, and continues to be, the proper course to follow, according to the 11-member panel's "Snake River Spill-Transport Review."

"Optimizing return rates for Snake River spring/summer Chinook and steelhead is a balancing act, since management scenarios that improve circumstances for one species may be detrimental for the other," the report says.

"The timing and relative benefits of transportation versus in-river migration vary with species, time of year, flow conditions, and the absolute and relative abundances of transported and in-river fish.

"Most existing data show that transportation in the late-April through May migration season benefits hatchery and wild Chinook, as well as hatchery and wild steelhead. However, the magnitude of the benefits in smolt-to-adult return ratios (SARs), fish travel times, and survival rates vary substantially among species, within the migration season, and between years. Data are insufficient to determine whether transportation benefits or harms Snake River sockeye," according to the review.

Adding to the vexing question are counterpoints, such as evidence that chinook and steelhead transported to the estuary exhibit more straying behavior upon their return as adults than in-river fish, failing to find their natal stream.

"We know what the stray rates are. We don't know what the impacts are," the ISAB's J. Richard Alldredge said of the potential dilution of native gene pools by an infusion of strayed fish. There also is a disease tradeoff.

"In-river migration likely entails lower risk of epizootics (i.e., local disease outbreaks that can rapidly affect many animals) due to pathogens or parasites, whereas crowded conditions in the barges increase this risk," the report notes.

The transportation vs. spill issue still presents more questions than answers, Alldredge told the Northwest Power and Conservation Council Wednesday. He concluded his presentation by donning a t-shirt with the lettering "Uncertainty. Something you can always count on."

"Some analyses of data presented here and elsewhere indicate that transportation between May 7 and May 20 benefits hatchery and wild Chinook, as well as hatchery and wild steelhead," the review said of a new strategy to cease spill for fish passage during that period.

"If transportation during this migration period is beneficial, then it could be argued that increasing transportation by terminating spill during this time would be even more beneficial," the report says. "However, other analyses presented here and elsewhere indicate that as spill increases, in-river survival increases and the relative benefit of transportation decreases.

"Increased spill may also benefit sockeye and lamprey, but definitive data are lacking. Further, terminating spill would eliminate the possibility of learning about the effect of partial spill during this critical period, thereby reducing opportunities for improved decision-making in the future."

"Transportation influences the success of in-river fish. Increasing the proportion of in-river migrants increases the density of smolts in the river. As smolt density increases, the proportion killed by predators will likely decrease because mortality due to predation appears to be depensatory (based both on theoretical expectations and limited empirical evidence)."

Preliminary results from 2006 and 2007 structural (spillway weirs) and operational changes (increased spill) have improved the survival of in-river migrating spring/summer Chinook, steelhead, and sockeye, according to the report. The effects will become clearer when adult returns from those years can be tallied.

"Spill-transport operations like those of 2006 and 2007 should be continued long enough to determine how much influence such operational changes have on downriver migration and total adult returns. Continuing recent spill-transport operations is advised to improve future evaluations of the trade-offs associated with spill and transport decisions," the ISAB recommends.

"In sum, the ISAB finds that structural and operational changes to the hydrosystem in 2006 and 2007 are not yet fully reflected in the data available for review in this report. Moreover, very few data are available to assess the impact of alternative spill-transport operations on species such as sockeye, coho salmon, and Pacific lamprey.

"Even the more plentiful data for Snake River spring/summer Chinook and steelhead do not yield unequivocal results about seasonal variation in the effectiveness of smolt transport," the report says. "Given the magnitude of uncertainty imposed by the nature and extent of available information, the ISAB continues to see merit in a strategy of 'spreading the risk' to balance the possible risks against the perceived benefits of juvenile salmonid transportation."

The ISAB review was produced at the request of NOAA Fisheries Service, the federal agency responsible for protecting 13 Columbia/Snake river basin salmon and steelhead stocks that are listed under the Endangered Species Act.

Usha Varanasi, science and research director for NOAA's Northwest Fisheries Science Center, in March requested that the ISAB address several questions related to the "relative survival benefit of alternative Lower Snake River spill and transport operations."

Related questions were submitted to the ISAB in April by the Oregon Department of Fish and Wildlife and the Columbia River Inter-Tribal Fish Commission.

The ISAB response is framed in the context of questions that the ISAB synthesized from those posed by these three entities.

The ISAB also recommends that:

-- Studies be conducted to reduce critical uncertainties related to the impact of spill-bypass-transport operations on downstream juvenile lamprey migration, including estimation of the population; evaluation of the effect of bar screen design on mortality and migration route; and estimation of mortality rates due to route of hydrosystem passage. Furthermore, the hydrosystem's impact on the entire life cycle of Pacific lamprey should be thoroughly investigated in a timely manner.

-- Further study is needed to define rates of mortality of sockeye smolts caused by partial descaling and injury for the various routes of passage through the hydrosystem during the peak migration period (mid-May to mid-June).

-- Evaluations of spill-transport operations should include studies designed to reduce uncertainties about relative amounts of straying for transported versus in-river fish for both hatchery and wild stocks of Snake River steelhead and spring Chinook.

The new review reiterated a perspective on spill included in a 1999 report that said "Spill: The general principle is that all juvenile passage alternatives should be evaluated against the baseline of spill. As an avenue of hydroelectric project passage, spill more closely mimics natural situations and ecological processes than other available routes. Spill should be considered as an alternative when the improvements anticipated from other bypass technologies are not large enough to meet the passage goals."

"That is to say, spill should be considered the default recommendation rather than simply one of the alternatives," the transportation-spill review says.

The ISAB report is posted on the Council's website: http://www.nwcouncil.org/library/isab/isab2008-5.htm

The ISAB, formed in 1996, provides independent scientific advice and recommendations regarding scientific issues posed by NOAA, the NPCC and Columbia basin tribes.