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NW Fishletter #256, January 8, 2009

[2] Salmon Go Acoustic At Research Confab
"...the benefits from modifying dam passage for fish was small potatoes compared to the huge vagaries they encounter in the ocean."

At last month's annual rendezvous of salmon recovery researchers in Portland sponsored by the Corps of Engineers, the take-home message was clear--the benefits from modifying dam passage for fish was small potatoes compared to the huge vagaries they encounter in the ocean.

But the message was delivered by someone who had invited himself, Canadian scientist David Welch, whose acoustic tag research has attracted a considerable amount of both flack and kudos, for its attempts at tracking juvenile salmon survival in the ocean.

Using a tag that's considerably larger than the one the Corps uses in its research, Welch is able to track fish down the Snake, into the Columbia and out in the ocean all the way to Southeast Alaska.

The Corps' tags are small enough to be implanted in young fall chinook, but don't work well in salt water and their battery life is much shorter. But the Corps hasn't been interested in monitoring fish survival past the estuary.

However, BPA funding has kept Welch's work going, despite recommendations from fish and wildlife managers to reduce it. They have long held that because he tags only a few hundred fish, his work doesn't represent the run at large.

But he has collected enough data to debate that point.

When he reported his 2008 preliminary findings last month, they corroborated his 2006 results that showed survival of his acoustic-tagged smolts from both the Snake and Yakima rivers tracked with survivals of PIT-tagged fish from 2006 and 2008.

And perhaps more importantly, his data shows that those in-river survival rates appear to be "roughly" the same above and below the hydrosystem. Welch said ocean survival may actually be worse than in the hydro system.

The results did not show any differential mortality between fish from the Snake compared to Yakima smolts, which traverse four fewer dams. The Snake fish actually had higher survival per distance traveled.

About 11 percent of the inriver migrating Snake smolts were detected off NW Vancouver Island, 9.3 percent of the barged Snake fish, and 10.7 percent of the inriver migrating Yakima fish, about 1,500 kilometers from their starting point.

That means about 20 fish from each inriver release of 200 fish were detected off Vancouver Island.

He concluded that the lack of any benefit from transporting juveniles through the hydro system "likely occurs because transport moves smolts between two environments with roughly similar rates of survival."

Welch didn't include his 2007 results because of tagging problems that year.

Welch came under fire recently for publishing results in a peer-reviewed journal PLOS-Biology that showed evidence that survival of migrating juvenile chinook in the undammed Fraser River was similar to that seen in the Snake and Columbia--where test fish passed eight dams.

The Fish Passage Center recently posted a critical review of Welch's paper on its Web site. Some state and tribal agencies have also criticized Welch's earlier findings that have raised doubts about "latent mortality" of fish that pass more dams or are barged.

NMFS PIT-tag researchers have shown no clear benefit to wild Snake spring chinook stocks from being barged through the hydro system, but even FPC results have shown some benefits to hatchery spring chinook from transportation.

NMFS research has also shown great swings in survival to adulthood from fish that migrate only a week or two apart--with migrating inriver fish usually showing better SARs [Smolt-to-Adult Return Rates] early in the spring and barged fish showing better SARs later in the season.

These findings have led NMFS to conclude that later ocean entry usually coincides with better overall survival.

Welch's group used only two release groups from the Snake and Yakima rivers, so his findings do not cover the time-spread that could capture a whole season's worth of ups and downs related to SARs.

Federal scientists have speculated that these fluctuations are due to fast changes in ocean conditions like upwelling, or the appearance of heavy salmon predators like hake or mackerel when waters are warm.

Welch said survival through the estuary was much better than previous years. This was backed up by the Corps' own acoustic research, reported by Geoff McMichael, of the Pacific Northwest National Laboratory in Richland.

McMichael said his group's preliminary 2008 survival estimates for spring chinook ranged from 65 percent to 94 percent, with fall chinook about the same. He said most spring chinook losses occurred in the lower 35 kilometers of the river. -B. R.

The following links were mentioned in this story:

NW Fishletter 254, Nov. 10, 2008

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