As shad anglers ready their darts and Dick Nites and keep a close eye on the daily count at Bonneville Dam, the East Coast fish are turning up in another and rather unexpected location this spring.
At least 108 were caught during weekly tribal warmwater gillnet test fisheries in the southern half of the lake in March and April, according to preliminary catch data the National Marine Fisheries Service shared with Northwest Sportsman.
While a few shad have apparently turned up in the 22,000-acre Pugetropolis lake in recent years, 2021’s numbers and the relative increase is a perplexing development for a puzzling species.
With the impact that these seagoing fish may be having on native and nonnative species alike in the Columbia “poorly understood” even after 140 years there, it’s unsettling news for Lake Washington watershed managers who are trying to improve the metro lake’s struggling Chinook, coho and sockeye runs, culturally and recreationally more important stocks to the region.
Shad feed on plankton, a diet that overlaps with that of salmon, while their fry provide forage for bass, walleye and other warmwater species. In theory, young salmonids might also benefit from the new prey base, as well as reduced predation by spinyrays because of it, but “the opposite may actually be true,” a fisheries student at a Northwest university wrote in a 2011 paper.
“American shad are excellent sources of energy, better than most other fish and crustaceans in that ecosystem,” stated KC Dill. “As a result some predators may experience a faster growth rate and possibly a larger size at maturation when replacing other organisms in their diet with shad. This may lead to higher consumption rates and, therefore, higher predation rates on salmon as well.”
May, could and possibly might as well be the middle name for a species officially known to science as Alosa sapidissima, the latter word meaning “most delicious.”
Indeed, this Atlantic seaboard food fish was released in the Sacramento River in 1871 by the U.S. Fish Commission. By the 1880s they had appeared in the Columbia River and their numbers slowly grew over the decades until spiking in the early 1990s and again in the early 2000s.
The last three years have seen the largest runs on record – a minimum of 5.8 million at Bonneville last year, 7.5 million in 2019 and 6.1 million in 2018, returns perhaps supercharged in some way by The Blob and warmer summers and waters.
They now vastly outnumber the Columbia’s native spring, summer and fall Chinook, coho, sockeye, chum, pink salmon, winter and summer steelhead, coho, bull trout and lamprey runs combined, and sometimes as many go past the dam in a single day as do most of those other stocks in an entire year. Mid-June 2020 saw back-to-back record daily counts of 570,329 and 588,969 shad.
And the dam count reflects only some percentage of the true shad run, much of which spawns below Bonneville. The U.S. Geological Survey estimates “as many 10 million to 20 million adult shad may enter the Columbia annually,” according to the Northwest Power and Conservation Council.
“The success of non-native American shad in the Columbia River is likely related to successful passage at the dams, good spawning and rearing habitats, and low exploitation by commercial and sport fishers,” USGS reports.
Despite their staggering numbers, given low market value and other factors, there is little commercial interest in shad. Last year, none were reported caught in the Columbia for the first time since 1980, but recent years have seen sport anglers keep as many as a quarter million.
Shad can make multiple spawning runs in their lifetime and some research suggests those rearing higher in the Columbia system enjoy better growth rates, “particularly in the Snake River reservoirs.” Biologists also found that some don’t go out to the Pacific by their first fall and instead rear up to two years in freshwater.
“Shad are an interesting puzzle – there are a lot of unanswered questions about their impact on the Columbia River ecosystem,” a state manager told me a couple years ago.
The fish are also found in Oregon’s Willamette, Umpqua and Siuslaw Rivers.
USGS maintains an invasive species database and it shows that since the late 1800s shad have also been observed in parts of Puget Sound, Grays Harbor, the Chehalis River, Skagit Bay and Hood Canal, along with waters all the way up into Alaska, but none in Lake Washington.
On Monday a WDFW biologist said that “a few shad have shown up in past netting exercises,” but this year there is also a “slightly higher number of them,” though it wasn’t clear if that was due to intensified netting or other factors.
Still, a county biologist noted there is concern about how fast the population might expand. The fish are broadcast spawners that seek out fine gravels to distribute and fertilize their eggs over.
The shad were caught during Muckleshoot Tribe efforts south of the Highway 520 bridge, with 28 in March and 80 in April, according to the data forwarded by NMFS. The week of April 18 saw the most caught, 73. The timing is a somewhat unusual signal, given that ocean-going shad typically don’t arrive in the Columbia till May.
The 108 shad represented 2.1 percent of the overall tribal catch of 5,024 fish. Those were split 69-31 between native and nonnative species. Largescale suckers and northern pikeminnow, both natives, represented 32.3 and 31.4 percent of the overall catch, followed by nonnative smallmouth bass at 20.8 percent and native cutthroat trout at 3.5 percent.
Also caught were two northern pike and one walleye, both nonnatives that could have only been illegally stocked in Lake Washington by bucket biologists.
The Muckleshoots consider the release of walleye in the system to be “criminal” and it was after spring 2015’s discovery of a dozen or so off Mercer Island by biologists that the tribe began a series of warmwater test fisheries, initially on Washington, then focused on Lake Sammamish.
The tribal test fishery is one of two efforts to gauge the lakes’ predator fish populations and what they’re eating. WDFW crews have been sampling the Lake Washington Ship Canal and last week reported catching what would be a new state record rock bass, another invasive whose numbers are skyrocketing in recent years, compounding efforts to save the lake’s runs of salmon.
The arrival of shad throws another curveball into the mix for an already much messed up system.