[3] Latest Barging Analysis Still Touts Survival Benefits

The latest NMFS analysis of PIT-tag survival data covering 10 years of barging Snake River fish past Columbia/Snake dams has shown that the strategy is still beneficial for spring chinook and steelhead most of the time, whether they are wild or hatchery bred.

The analyses has been complicated by changes in operations and dam spill since 2006, when all juvenile fish were returned to the river from bypass systems early in the season, rather than putting them in barges. The new report says results may have changed from earlier years, but such differences are hard to pin down.

The new analysis not only examined smolt-to-adult return rates between inriver migrants (detected only once at a Snake dam) and transported fish, but also looked at smolt-to-adult returns [SARs] between the run at large, which includes bypassed fish that returned to the river, plus the non-detecteds and the transported groups.

"The results indicated that transported fish had significantly higher rates of return compared to migrant fish over the majority of the outmigrations," said the December 2009 report, which is not yet available on the Web.

"These results essentially corroborate results produced by COMPASS modeling, the outputs from which formed much of the basis for the 2008 BiOp. In our re-analysis, most cases when transported fish had lower return rates than migrants occurred in the early part of the migration season."

The review cited findings from the Independent Scientific Review Panel's 2008 report that found hatchery and wild chinook, and hatchery and wild steelhead all benefited from barging between May 7 and May 20.

The panel noted increased survival of juvenile migrants to Bonneville Dam had increased from structural (removable spillway weirs and other modifications at dams) and operational improvements (more spill) in 2006 and 2007, but was uncertain how "this would change relative SARs of transported and migrant fish without seeing the adult returns. The ISAB was also concerned about the effects of increased straying caused by transport."

The NMFS report says since 2006, the ratios of SARs between barged and inriver migrants for wild and hatchery chinook and wild steelhead seem close to patterns observed in earlier years when all bypassed, non-tagged fish were barged, but the T:M [Transport:Migrant] ratio for hatchery steelhead may have changed--"the only instances in the 11 years of data of significantly lower returns for transported hatchery steelhead occurred in the early parts of the 2006 and 2007 migration seasons."

Citing two other analyses, the review cautioned that SARs from the PIT-tagged fish were likely lower than those from the unmarked population.

More data to be collected in the next two years, 2010 and 2011 adult returns from the 2008 and 2009 outmigrations, will show if the recent trend in hatchery steelhead returns is maintained. The review noted that PIT-tag detections of adult hatchery steelhead that migrated in 2008 "already are near 4 times higher than the total adult returns for hatchery fish from all the preceding years combined."

The report also took a crack at analyzing results from the 2008 spring chinook outmigration, even though researchers can only use returns from jacks in 2009. So far, it shows a definite benefit for transported fish throughout the 2008 migration season.

The review said that changes need to be made to tagging strategies to get a better idea just how well the new management regime is working. It said more fish need to be tagged and put into the barges before May 1. -B. R.

Subscriptions and Feedback
Subscribe to the Fishletter notification e-mail list.
Send e-mail comments to the editor.

THE ARCHIVE :: Previous NW Fishletter issues and supporting documents.

NW Fishletter is produced by Energy NewsData.
Publisher: Cyrus Noë, Editor: Bill Rudolph
Phone: (206) 285-4848 Fax: (206) 281-8035