[2] BPA-Funded Acoustic-Tag Study Gets Nod From Peer Review
The number of dams salmon smolts must pass on their migration to the sea has little impact on their long-term survival, according to new research published June 30 in the peer-reviewed Canadian Journal of Fisheries and Aquatic Sciences.
For years, most state and tribal biologists held the opposite view, namely, that the more dams young fish encounter during their migration, the more stress they accumulate, which leads them to die at a higher rate at some point in the future. But biologists have never been able to prove their hypothesis.
The work is the result of years of preparation by Canadian researcher and consultant David Welch, head of Vancouver, B.C.-based Kintama Research. Welch has led an effort to develop a deep sea ocean tracking system on the continental shelf, called POST (Pacific Ocean Shelf Tracking), and is partly funded by BPA (about $7 million through the end of this year).
Welch co-authored the report with Ph.D. candidate Erin Rechisky and has reported on his findings before, but mostly in non-peer-reviewed settings, such as the Northwest Power and Conservation Council.
The article reports results from acoustic-tag tracking data collected in 2006 from two groups of juvenile salmon, one from the Yakima River that crossed four dams and another from the Snake that crossed eight dams before they reached the sea. The two groups showed nearly identical survivals--about 29 percent plus or minus four or five percent--to a point north of Willapa Bay, off the southwest Washington coast, where an acoustic detection array was placed on the bottom.
Welch used Yakima fish because their smolt-to-adult return rates were thought to be generally quite higher than fish from the Snake, though, in recent years, there has been some questioning of that notion from adult PIT-tag returns.
Welch reported his preliminary results in late 2006, after he successfully lobbied the Power Council for adequate funding, following efforts by state and tribal fish agencies that actively sought to cut his BPA money in half.
That year, some of his detection samples were extremely small, especially off the site at the northern end of Vancouver Island.
In the latest article, the authors reported that some acoustic-tagged chinook were reported at arrays off Vancouver Island and Southeast Alaska in 2006. But the low numbers of detections and the fact that smolts arrived at both locations within two days of the arrays' deployment kept them from making reliable survival estimates at these points.
"However," the researchers wrote, "the detection of four Snake and two Yakima smolts on the Vancouver line, some 1,500 km distant from the release site (30 days travel time from Willapa Bay for both populations), and the detection of two Snake River smolts on the Alaska line (and none from the Yakima population), some 2,500 km from the release site, is inconsistent with the delayed mortality hypothesis."
Over the years, Welch has had plenty of critics. Both federal scientists and the Fish Passage Center have panned his work, mostly for using young fish that are too big to be representative of the general populations.
But it couldn't be helped. Welch's group had to raise them extra big to contain the large tag and battery that was surgically implanted in each fish. The batteries lasted for several months.
The extra time it took to rear them also meant they migrated downstream a couple weeks later than the populations they had come from. That raised another issue--if the different groups didn't enter the ocean at the same time, their survival rates may not reflect similar ocean conditions, where predator populations come and go.
Ocean entry timing plays a huge factor in ultimate survival, according to NMFS PIT-tag research, which has shown that differences of only a week or two can easily double or triple survival to adulthood, depending on the vagaries of nutrient upwelling and predator movement, especially when waters are warmer.
Others have pointed out that differences in mortality between the two groups might show up later, and the newly minted paper acknowledges this possibility--"the survival disparity observed in adult return rates may develop later in the marine life history phase."
The authors acknowledged their study limitations--the large fish (longer than 140 mm) and the two-week-late release, as well as the non-simultaneous arrival for the two populations to the array off Willapa Bay--and said these issues will be addressed in future work.
The authors said it is plausible that delayed mortality may operate on smaller fish, but their findings showed that "the number of dams passed within a migration segment did not affect survival" and also backed up other findings showing direct inriver survival has improved in recent decades, "possibly to the level of an undammed river."
The new paper referred to a 2008 peer-reviewed publication of Welch's group that looked at smolt survival in the Fraser and Columbia rivers and found them comparable.
Regional scientists have been arguing about that ever since December 2005, when Welch presented the initial findings from his 2004-2005 Fraser data to the Power Council. The preliminary data indicated chinook survivals in the undammed B.C. river were similar to the highly impounded Columbia/Snake system.
Welch does like to shake things up, and he's had heated debates with some other agencies, mainly the Corps of Engineers, over the direction of acoustic-tag research. The Corps uses smaller tags for smaller fish, but they can only be used in fresh water. And there is some question about how they perform compared to PIT tags--some evidence shows that the Corps' inriver acoustic survival data tracks 10 percent or more lower than PIT-tag data.
Last winter, Welch invited himself to the Corps of Engineers' annual research review in Portland, and presented his latest results, including 2008's preliminary findings that showed two similar groups of smolts both showed similar survival rates all the way up the coast to the northwest tip of Vancouver Island.
At that time, he reported that 11 percent of the acoustically-tagged Snake smolts that migrated inriver were detected in his receiver array off the northwest tip of the island, compared to 9.3 percent of the barged Snake fish, and nearly 11 percent of the inriver migrating Yakima fish.
Welch told NW Fishletter that a new paper is in the works that deals with his 2008 data.
The new paper says it is still unclear whether the entire size range of the Yakima and Snake fish, along with wild fish, show similar survival and behavior to the smolts in this study, but the authors called it a "significant scientific milestone because the POST array allowed for a direct test of a key hypothesis concerning delayed mortality of a population of Snake River spring chinook in the ocean."
They said future improvements in design will allow them to study marine survival throughout the size range of the Snake spring chinook and other ESA-listed salmon in the Columbia Basin. -B. R.
The following links were mentioned in this story:
Canadian Journal of Fisheries and Aquatic Sciences
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