Officials with the Washington Department of Fish and Wildlife say the 6.85 million shad that passed through Bonneville's fish ladders as of June 27 already constitute a record for the largest shad run ever counted at the dam, and the season's not even over yet.

It beats last year's total shad escapement over Bonneville of 6.1 million, which broke previous records for the highest number counted there since they started keeping track in 1946. That run wasn't over until Aug. 31.

The numbers--which have ranged from 1 million to 6 million since the late 1980s--are only a fraction of the 10 million to 20 million adult shad that the U.S. Geological Survey believes may enter the Columbia River annually. Most of them spawn from May to July in the estuary below Bonneville. But many also migrate up the Willamette River, as far as Priest Rapids Dam on the mainstem Columbia, and into Hells Canyon on the Snake River.

"The East Coast would kill to have numbers like this," Bill Tweit, Columbia River fishery coordinator for the Washington Department of Fish and Wildlife, told NW Fishletter. "They're working at recovering shad back there, and we're scratching our heads going, 'What does this mean?"

American shad are not native to the Pacific Coast. These 5- to 12-pound fish were introduced from the east, released in the Sacramento River in 1871.

By 1885, some of California's shad had already discovered the Columbia River, and more were planted. Like salmon, they are anadromous--migrating to the ocean for three to five years before returning to freshwater to spawn. Unlike salmon, they spawn in open water rather than in gravel beds, and can return to the ocean and spawn multiple times.

Tweit said although there have been some concerns about shad clogging up the fish ladders for a handful of days in mid-June when hundreds of thousands pass through Bonneville daily, his agency hasn't identified any conflicts with their efforts to recover salmon and steelhead in the basin. "That's in large part because we don't understand either their role or their impact in the Columbia right now," he said.

Scientists have surmised that they may be doing some good--bringing ocean nutrients back to the freshwater environment at a time when salmon and steelhead are lacking, and serving as prey to sturgeon, birds, or other predators. A member of the herring family, shad are likely too small as juveniles to take pressure from predators off juvenile salmon or steelhead, Tweit noted. "Eating tiny little shad fry is quite different than eating salmon smolts," he said.

Tweit said he's not suggesting there aren't negative impacts to salmon and steelhead. His agency just hasn't found any.

"I think it's interesting--all the work we do to monitor salmon yields very little information about what shad are doing," Tweit said. "Other than the fish ladder counts, we don't have a real clear idea of what they're doing."

Tweit said shad are popular among sport fishermen, who can catch as many as they like, with no daily limits. "And it's fairly well known," he said. "They fight a little and jump a little, and if you're down there during the month of peak passage, you're going to catch fish," he said.

However, interest by commercial fishermen has been lacking.

Part of the problem may be culture. In Eastern states, shad--although boney--are considered quite savory, and there's a strong market for them. But in the Pacific Northwest--where salmon have always been the preferred fish--the infrastructure to catch and process shad never developed.

Another issue may be timing of the run, and the need to ensure Endangered Species Act-listed fish aren't harmed.

According to this year's joint report on fisheries stocks by Washington and Oregon's fish and wildlife departments, the two states have explored the use of alternative gear to catch shad and minimize impacts to salmon and steelhead. Purse seines were used in 2011, 2012 and 2016, and a beach seine was used in 2014 under experimental gear permits issued by the Oregon Department of Fish and Wildlife.

"In 2013, one experimental gear permit for a purse seine was issued, but no fishing occurred due to a lack of market demand," the report said. "It is expected that harvest opportunity using these alternative gear types would be allowed in future fisheries if demand exists."

Tweit said both Washington and Oregon continue to be interested in developing a commercial fishery.

He said NOAA Fisheries scientists who study the Columbia River estuary may know more about impacts of shad on salmon and steelhead. Efforts by NW Fishletter to reach NOAA scientists who study the estuary were unsuccessful.

Ryan Lothrop, WDFW's Columbia River fishery manager, said there are plenty of potential negative impacts to consider--such as risks of disease and direct competition with salmon for food, either in the estuary or the ocean.

But if shad fill the same niche in the Columbia as anchovies do in Puget Sound, these large numbers may bode well for future salmon and steelhead returns. Lothrop said a recent study there found that large anchovy populations correlate to improving conditions for salmon.

Without the studies, they can only hope the same is true for shad, he said. "If they're coming back in record numbers, it could be a silver lining--a sign of changing conditions in the ocean," Lothrop said.

Tweit said whether the impacts of shad on Columbia River salmon are good, bad or indifferent, a look at what's causing their population explosion could offer some important insights.

K.C. Mehaffey covers fish issues for Clearing Up, and is editor of the NW Fishletter. She joined the NewsData writing team in February 2018. From lawsuits to scientific studies, she is enjoying the deep dive into the Columbia Basin's many fish topics.