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NOAA says Snake River Spring Chinook
Return Rates as Good as They Get

by Bill Rudolph
NW Fishletter, January 16, 2004

NOAA scientists and policymakers, rushing to get several products out the agency door before the end of the year, left several large presents under the regional Christmas tree, in the form of updated white papers that have corralled current research on Columbia Basin salmon and the dams they cross. They are expected to play a big role in writing a new Biological Opinion for the basin and contained several optimistic predictions for future runs.

Perhaps the best news from the research is that ESA-listed wild spring chinook have been returning to the Snake River at an average rate of nearly 4 percent over the past few years, a level not seen since the mid-1960s, before the last mainstem dams were constructed.

For now, scientists say things are relatively rosy. Escapements have been going up for six straight years--the longest stretch since record-taking began in the 1960s. And they say there's plenty of evidence to predict that adult runs will stay high at least through 2006.

Yet the latest research still finds "little or no relationship between flow volume and survival."

While NOAA scientists gave the region a nice Christmas present, the agency's policy makers weren't being so generous. On Dec. 23 NOAA released its 2003 BiOp check-in report to gauge progress on BiOp implementation, even though the plan is in legal limbo during the current remand. A new draft BiOp has been promised by the end of March.

According to the check-in, action agencies (BPA, BuRec, Corps of Engineers) have not fully met expectations, "but are capable of timely resolution of the shortcomings."

The check-in said several actions are behind schedule, including the completion of priority subbasin assessments and plans, genetic monitoring plans for hatcheries, and research and monitoring plans to evaluate progress by 2005 and 2008.

But in a press release that accompanied the report, NOAA Fisheries said it was continuing to work with other federal agencies to review the BiOp, "to ensure that it is legally and biologically defensible."

A federal judge threw out the old BiOp last May because it didn't clearly say that offsite mitigation efforts were reasonably certain to occur. Since then, the agencies involved have been trying to decide whether to satisfy the judge's technical concerns or do a major re-write.

That's where the updated white papers come in. On Dec. 23 NOAA Fisheries' Seattle Science Center released preliminary drafts for public comment, even before NOAA Fisheries had completely vetted the documents in-house.

Scientist Bill Hevlin of NOAA's Portland-based hydro operations group said his office saw the drafts for the first time Dec. 23 and it would take some time to go through them.

The draft that covered hydro system effects on salmon populations contains some very up-to-date information that is sure to garner comment from state and tribal fishery agencies. For instance, NOAA scientists reported that smolt-to-adult returns [SARs] to the Snake River from the drought-plagued 2001 migration have been calculated at 1.5 percent, much better than fish managers had expected, even though most of the fish were barged and the 3-ocean component (fish that spend three years at sea before returning to the river) won't show up until next spring.

"This return rate already exceeds total SARs for all Snake River spring-summer chinook outmigrations between 1976 and 1997," the scientists said. They also noted that returns for Snake steelhead and fall chinook have increased by a comparable amount over the past three years, with median counts three to four times (or more) higher than during the previous period.

With new data from the past couple of years, the study said that transported spring chinook survived to adulthood, on average, at a rate that was only about two-thirds that of in-river migrating fish, but that fish barged from Lower Granite Dam fared about the same as in-river migrators.

Barging a Mixed Bag
The results suggest that survival of barged spring migrants may improve if they are only picked up at Lower Granite dam, rather than at the two other dam sites on the lower Snake where barging is now conducted.

But the issue is complicated, since barged spring chinook and steelhead migrants of hatchery origin survived to adulthood better than their inriver brethren.

However, scientists said that within-year variations in survival between barged and inriver migrants were so high that an annual ratio of transport survival to inriver survival "should not be used as a basis for management decisions." In some cases, like during the 2000 migration, the transported fish returned at higher rates and provided large survival benefits for steelhead as well.

With little data for fall chinook, they said the BiOp's estimate of barged fish surviving at only one-fifth the rate of inriver fish "is reasonable, albeit highly uncertain," since fall chinook do not migrate as quickly as other salmonids, which makes measuring their survival through the system difficult. Results so far show that fall chinook migrating after Sept. 1, when both spill and barging have ended, have a SAR rate of four times higher than earlier migrators--1.29 percent compared to 0.32 percent.

For inriver migrating spring chinook, questions have been raised about higher mortality rates for those passing lower Snake dams via bypass systems, compared to fish that pass through turbine bays or over spillways. But the latest report says that wild chinook detected only at Lower Granite had "significantly higher" return rates than fish not detected at all (which means only turbine or spillway passage).

Size Matters
However, scientists said differential adult return rates don't necessarily mean that some bypass systems are worse for fish than others--or that simply swimming through one makes a fish less fit. Citing newer data from 1998 to 2000, they point out that "return rates are strongly influenced by the size of individuals and the timing of their outmigration."

Smaller fish may tend to be more easily guided into bypass systems by turbine screens and then routed to barges, which could bias the survival data on the low side, the report said.

The scientists also hypothesized that the act of PIT-tagging fish has a greater negative impact on smaller wild fish, which could account for the fact that hatchery fish have shown higher SARs than wild fish in recent years.

But the region cannot rely on good ocean conditions forever, since it is a cycle that will shift to a more unproductive mode at some point. "With predictions of increased global warming in the near future, ocean conditions may actually become worse than any we have experienced," the scientists said. "For these reasons, we must continue to assess the impacts of the hydro system in the context of all impacts, including impacts occurring in both seawater and freshwater habitats."

Related Sites:
NOAA's 2003 BiOp check-in report

Bill Rudolph
NOAA says Snake River Spring Chinook Return Rates as Good as They Get
NW Fishletter, January 16, 2004

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