[4] Salmon-Munching Bass Getting A Closer Look

A popular Northwest game fish, smallmouth bass, may eventually be found on 'Most Wanted' posters up and down the Columbia River as a major killer of young ESA-listed salmon. Like northern pikeminnow, they may end up with a price on their heads.

Smallmouth bass are a non-native species in the Northwest that like to dine on juvenile salmon and have become hugely prolific throughout warmer waters in the region. But there is one big problem--they are currently classified as a game fish in the state of Washington, rather than a nuisance, so they are managed and protected.

Regional fish managers met in late September in Portland to examine salmon predation by bass, channel catfish and walleye pike, and the possible role the millions of Columbia River shad may play in the interactions.

The workshop was mandated in the new hydro BiOp, under RPA (Reasonable and Prudent Alternative) 44, as a way to begin efforts to implement "piscivorous control measures to increase survival of juvenile salmonids."

It's the first step in a process that may give anglers a chance to catch bass in a bounty program like the one developed for northern pikeminnow, for which BPA spends $3.7 million annually to pay anglers to rid the rivers of nearly 200,000 salmon predators. However, at this point, biologists don't know if the bass play a bigger role than other predators munching on salmon

Managers have found it hard enough to measure the success of the pikeminnow program, though Oregon Department of Fish and Wildlife's Erick Van Dyke told workshop participants the mean size of the pikeminnow appears to have decreased over the years--a major goal of the program. The smaller pikeminnow are thought to have less impact on migrating juvenile salmon.

Washington Department of Fish and Wildlife biologist Anthony Fritts reported that a four-year study in the Yakima River found that low summer flows in the lower river increase water temperatures and attract bass spawning activity.

Researchers found that smaller smallmouth bass were most predaceous and grew large enough to eat salmon by age 2. It's thought that older bass concentrate on other prey than salmon. The bass also tended to focus on the smaller naturally produced fall chinook instead of the larger hatchery-produced yearlings.

According to a recent synopsis of the meeting, "Fritts also noted that a lot of people really like bass fishing, so there could be substantial opposition to removal."

Fritts also pointed out the high level of toxins in the lower Yakima smallmouth bass, "so we should be cautious about promoting a fishery."

The University of Idaho's David Bennett reported on studies from the 1980s about predation in the Snake River, while noting that 60 percent of species in the Snake were non-native. He said channel catfish were the "surprising predators" in the early 1980s study of Lower Granite Reservoir.

He also said there was some evidence that pikeminnow predation on chinook above Lower Granite was slightly lower per surface area than in John Day Reservoir.

Other studies from the 1990s showed that up to 7 percent of the naturally produced subyearling fall chinook were consumed by smallmouth bass in Lower Granite Reservoir in low-flow years, but predation was considerably less when flows were higher. This makes sense, because other studies found that both smallmouth bass and pikeminnow are "sight feeders," and the increased turbidity from higher flows would likely reduce their success.

Bennett said modeling suggested that sport fishing wouldn't put much of a dent in bass populations. But others who attended said concentrating fishing effort at some of the dams might be the most productive way to reduce predation by bass.

"We know we have a problem, but we need more studies," said Shane Scott, a consultant for river users, who attended the meeting.

But the difficulties for anglers to target the age-2 bass have led some to question whether such an effort could be nearly as successful as the bounty program for pikeminnow--in which an angler can make $4 for each fish turned in, and more if large numbers are caught. But Scott said there is some evidence larger bass are eating smolts at dams.

BPA reports that more than 3.2 million northern pikeminnow have been removed from the Snake and Columbia rivers through the sport reward program since 1991. Last year, 191,154 northern pikeminnow were turned in; as a result, northern pikeminnow predation on juvenile salmon in 2007 was cut by an estimated 37 percent.

BPA's John Skidmore estimated that four million to six million smolts are saved every year through the current program. He said it was too early to say whether a program is likely to be developed to reduce the bass numbers. He did say the workshop results will be sent to NOAA Fisheries, which will collaborate with regional agencies in the next step towards building a policy

In July, the Independent Scientific Advisory Board recommended that state fishery agencies declare open season on species such as smallmouth bass and channel catfish that are not native to the Columbia Basin. It's sure to give some fish managers heartburn because programs are in place to enhance the numbers of some of these predators.

The science panel said the non-native species issue should get a boost in priority equivalent to other important concerns like habitat loss, climate change and human population growth and development. -B. R.

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