the film
Economic and dam related articles

Marathon Fish Research Review Comes Up With Some Winners

by Bill Rudolph
NW Fishletter, November 26, 2002

The US Army Corps of Engineers hosted its annual research review in Portland last week, where biologists and engineers gathered to hear the latest results of dozens of studies being conducted on the mainstem Columbia and Snake rivers to help improve fish passage at federal dams. The review gave other federal scientists a venue for announcing more good news about overall fish survival in the system.

It took four days' worth of presentations to cover more than 80 projects that represented $30 million in research funding over the past year--with the preliminary results from the Corps' removable spillway weir (RSW) at Lower Granite Dam taking the lion's share of the limelight. The huge prototype steel structure is located in front of one of the dam's spill gates and creates a gigantic waterslide for juvenile fish to ride past the dam. It has become the pride of the Corps, the $12 million 2-million-pound gorilla of all the projects under study.

The early results with the RSW show that more fish pass the dam while less water is being spilled than under current conditions, where fish must pass over the spillway through open gates about 40 feet below the surface of the reservoir.

Results from this year's testing showed that 56 percent to 62 percent of the fish passed over the RSW with only 9 percent of the water discharge, while the regular spillway passed 17 percent to 22 percent of the fish with 22 percent of the water discharge. Together, the RSW and spillway passed 73 percent to 78 percent of the fish while discharging 31 percent of the water passing the dam. Translated into plain English, it means more fish go over the dam while more water can be routed to the powerhouse.

Early results also showed that the prototype RSW significantly reduced the time it took for fish to pass the dam, especially during low flows. A survival study conducted with balloon-tagged fish in the fall of 2001 showed that about 98 percent of the smolts survived the RSW route 48 hours after passage, compared to 100 percent survival via the regular spillway. After the fish passed the dam, the tags inflated and the fish were retrieved on the surface of the water below the dam in about 15 minutes. The novel tagging operation recaptured over 99 percent of the 520 test fish.

The 50 foot-wide RSW was also evaluated by hydro-acoustic sensors that tracked fish movement towards the weir under different operating conditions. Unfortunately, due to a turbine outage at Lower Granite and high runoff that forced spill, results were only statistically valid for a 10-day period in May. Nonetheless, the results were stunning.

Spill effectiveness (fish-to-water ratio) was highest in the scenario with the least spill--only 8 Kcfs/hour--and was lowest in the scenario with the most spill, 29 Kcfs/hour. The RSW with 8 Kcfs spill passed 78 percent of the juvenile fish, while the BiOp-mandated spill level, governed by a 120 percent dissolved gas limit, passed 74 percent of the fish while spilling 42 Kcfs. The researchers reported that it took about 3.5 times as much water under the gas cap scenario to pass nearly the same number of fish when the RSW was open with 8 Kcfs spill in the rest of the dam's spillway.

The atmosphere of the meeting was positively giddy after the RSW presentations. One presenter even suggested to the rest of the audience that "it's still not too late to get on the bus!" But several biologists who spoke to NW Fishletter after the session said it was possible that an RSW could be much less effective at another dam because the physical conditions at Lower Granite, together with the way river conditions route fish passage, may skew the RSW's efficiency upward. BPA is pushing for further study of the system, hoping it will support installation of the weirs at Ice Harbor and Lower Monumental dams.

Another potential difficulty with an RSW installation is its effect on collecting fish for transport. By routing more fish over the spillway instead of to a dam's bypass system, fewer fish are available for transport downstream via barge. Last spring, so many fish were routed around Lower Granite's bypass system by the RSW that a NMFS tagging crew had a hard time PIT-tagging enough wild chinook for a survival study under way at the time.

More Survival Studies

NMFS scientists were also on hand with their latest analysis of how well fish transported down the Snake were doing compared to their inriver migrating brethren. Scientist Doug Marsh said it was another good year for returns on the Snake River. With adult returns now complete for spring chinook that migrated to sea in 1999, Marsh said preliminary results showed that the ratio of returning hatchery fish transported downriver to inriver migrants was 1.3, which means transported fish showed a 30 percent survival advantage when they returned as adults. Wild fish fared even better from the barge rides, with a transport/inriver [T/I] ratio of 1.8. In lay terms, that's an 80 percent better survival rate than inriver migrating wild chinook. Marsh said the ratios were based on inriver fish not detected at a Snake River dam below Lower Granite.

For year 2000 salmon releases, Marsh said preliminary results show that the preliminary T/I for wild fish is 1.2, with next year's returns needed to complete the analysis.

Wild steelhead returns from 1999 releases showed even better results than the spring chinook data, with the preliminary T/I for hatchery fish pegged at 1.4 and wild fish estimated at 2.6. For 2000, the preliminary wild steelhead T/I was 1.9.

Marsh reported that smolt-to-adult returns (SAR) for Snake spring/summer chinook for 1990 releases showed a 2.3 percent SAR for hatchery fish and a 2.01 percent SAR for wild fish. For 2000, with more adult fish to count next year, preliminary data showed that wild fish, so far, are piling up a better SAR than hatchery fish, 0.91 percent compared to 0.5 percent for hatchery fish.

But the NMFS scientist reported on an issue that has been the subject of some consternation for federal biologists. For 2000 steelhead releases, Marsh said NMFS sees an SAR averaging around 4 percent for returning fish that migrated out of the Snake before the middle of May. But after that date, few if any steelhead have returned from the 2000 outmigration. He said a possible explanation is some kind of early regime shift in the ocean.

"This drastic change has to be related to the ocean," Marsh said, noting that early returns from the 2001 outmigration look similar to those in 2000.

Overall juvenile survival through the hydro system was similar to or even greater than recent years, excluding 2001's drought-plagued migration. NMFS' Bill Muir reported that Snake spring chinook averaged 66 percent survival from hatcheries to Lower Granite Dam and about 50 percent survival from the tailrace of Lower Granite to the tailrace of Bonneville Dam. Steelhead survival through the hydro system was about 27 percent this year. The scientists also estimated fall chinook survival from McNary Dam to the John Day tailrace at nearly 76 percent, a bit higher than in past years. (see dampool.htm for comparisons)

Another group of scientists from Oregon State University surgically implanted radio transmitters into steelhead and fall chinook to evaluate differences between barged and inriver migrating fish in an attempt to find evidence of delayed mortality. They tracked the fish from below Bonneville Dam to the Columbia estuary, using fixed-receiver sites, boats and aircraft.

Most fish migrated successfully, with inriver migrants exhibiting an edge over barged fish. Other work by the same group showed survival of barged steelhead released below Bonneville was higher than for inriver migrants in two out of three sample groups. The study estimated that maximum mortality in the estuary this year for the groups ranged between 43 percent and 51 percent for transported steelhead and between 29 percent and 65 percent for run-of-river fish, with most mortality occurring in the lower estuary.

A NMFS study that looked at adult fish survival in recent years found that an earlier trend showing lower return rates for wild spring chinook that were routed through multiple bypass systems at lower Snake dams "no longer exists." NMFS scientist John Williams reported that the large increase in adult returns that began with the 1999 outmigration still shows a slight downward trend for hatchery fish, but that could be caused by the differences in the quality of fish detected versus those not detected.

Other presentations dealt with many site-specific issues, including passage survival through turbines and spillways, adult passage, tern predation, lamprey migration, and effects of water temperatures on fish migration. But none may be as important for making immediate improvements as a study that looked at juvenile passage survival at Ice Harbor Dam.

Preliminary results showed only about an 89 percent survival rate for spring chinook at the dam, about the same as turbine survival. No one is sure why survival is so low there, but some suspect the stilling basin below the dam may be more lethal to fish than previously thought. At most other federal dams, spillway survival is on the order of 98 percent. Given that the current BiOp calls for 80 percent of spring and summer flows to be spilled at Ice Harbor, a reduction in spill could save millions for the cash-strapped power agency. BPA has the issue on its wish list, suggesting that an RSW located there might just be the answer.

Bill Rudolph
Marathon Fish Research Review Comes Up With Some Winners
NW Fishletter, November 26, 2002

See what you can learn

learn more on topics covered in the film
see the video
read the script
learn the songs
discussion forum
salmon animation