A new study commissioned by the Willamette Riverkeeper nonprofit found that freshwater mussels, a key indicator of river health and water quality, are not reproducing in one swath of the river 20 miles upstream from Corvallis (Andrew Theen/Staff)

One of the largest known mussel beds on the Willamette River, home to tens of thousands of mollusks that can live for up to a century on the river bottom, appears to be in poor health.

The mussels are not reproducing, according to a study released this week by the nonprofit Willamette Riverkeeper.

Because the mussels can live for as long or longer than humans, it’s worrisome researchers found a large healthy older population but no juveniles. “At some time in the past, the habitat was suitable for mussels,” the study said, “but conditions within the lifespan of this aged population have changed.”

Don't Edit

Researchers counted at least 40,000 Western pearlshell mussels in a channel near Norwood Island on the Willamette River (Andrew Theen/Staff)

Celeste Mazzacano, a veteran freshwater mussel scientist, conducted the research along with Willamette Riverkeeper staff and volunteers this summer. It's the most in-depth look at the health of the freshwater mussel known as the Western pearlshell in the Willamette River system.

It’s not great news.

Once ubiquitous across the West, several species of freshwater mussels appear to be in decline. Western pearlshells are the most common species in the Pacific Northwest, but little is known of their overall health and range. Experts say the mussel’s fate is tied to a smorgasbord of environmental and human factors -- climate change, agricultural runoff, a decline in salmon and steelhead populations and fluctuating flows and temperatures on heavily dammed rivers of the West.

Don't Edit

Mussels can be hard to spot on the river bottom, where they sit and filter feed (Photo courtesy of Travis Williams/Willamette Riverkeeper)

Mazzacano said mussels are important to freshwater ecosystems because they filter out particles and bacteria such as E. coli and feed on organic material and plankton.

They provide essential habitat for insects, too, which are a key food source for many river creatures.Their decline, Mazzacano said, should be important to anyone who cares about native fish like salmon and steelhead. Conversely, the fish help distribute the mussels’ embryos, which latch onto fish gills or fins.

Mazzacano said the animals are also significant to Oregon’s Native American population. Some tribes, like the Umatilla and Warm Springs, are working to reintroduce mussels to rivers where they were historically a source of food and vital for cultural reasons.

Don't Edit

Travis Williams snorkels in search of freshwater mussels near Norwood Island on the Willamette River (Andrew Theen/Staff)

Mussel declines and reproductive issues are well documented in the eastern half of North America, where several species are classified as threatened or endangered, and government resources and attention have helped pay for population studies. But the western population is less well-known. No mussel is listed as threatened or endangered in Oregon.

Some Oregonians are trying to change that.

Don't Edit

Don't Edit

Don't Edit

Andrew Theen/Staff

Travis Williams, Willamette Riverkeeper’s executive director, snorkeled a 120 mile stretch of the river this summer along with five other people. The extensive river survey indicated the area immediately adjacent to Norwood Island, a 90 acre area about 20 miles upstream from Corvallis, was home to an unusual and abundant cluster of mussels.

On Monday, Williams stood on the edge of the island in a dry suit holding three of the palm-sized mussels. The Long Tom River intersects with the Willamette nearby, and Williams said the shallow channel offers ideal habitat. According to the study, at least 40,000 mussels line the river bottom here.

“They’re pretty magnificent animals,” Williams said, holding one of the bivalve shells, which blend in with the river bottom and are difficult to spot.

Don't Edit

A tree-lined area of the Willamette River, about 20 miles upstream from Corvallis (Andrew Theen/Staff)

Willamette Riverkeeper, which has helped manage the island for the past several years, bought the property for $70,000 this year. Williams said he first started paddling through the area of Norwood Island in 2002 and noticed the mussel bed, which he described as “mind-blowing.” That discovery prompted years of interest in the invertebrates and eventually the 2017 study.

Williams hopes to drum up more interest to study the mussels in Oregon and help protect them, and he plans another study next summer.

A separate report, release last month by the nonprofit Xerces Society for Invertebrate Conservation, Nature Conservancy, Confederated Tribes of the Umatilla Indian Reservation and a North Carolina-based consultant group, raised warning flags about the extinction risk for a variety of mussels in the western half of North America.

The report compiled thousands of records dating back to the mid 1800s about mussels.

Don't Edit

Norwood Island on the Willamette River is a 90 acre parcel about 20 miles upstream from Corvallis (Andrew Theen/Staff)

Emilie Blevins, a conservation biologist with Portland-based Xerces Society, said the mussels are still pretty widespread in the west, but declines are occurring in new areas like the Willamette.

The report classified the Western pearlshell as “near threatened.”

Blevins said more research needs to be done. “For mussels to persist into the future, it’s going to require us to protect the existing populations,” she said.

Michele Weaver, Oregon Department of Fish and Wildlife endangered species specialist, said the agency is aware of the general decline in mussels nationally but acknowledged little is known about the overall status of western pearlshell in Oregon.

Don't Edit

A dead Western pearlshell pictured at Norwood Island. It's illegal to remove or move the invertebrates without a permit (Andrew Theen/Staff)

Other freshwater mussel species were included in a 2016 conservation strategy intended as a blueprint for how to protect potentially vulnerable species. Three other freshwater mussel species made the list.

Mazzacano, the mussel researcher and scientist, said the good news is that conservation projects have been successful in the past.

It’s possible to bring back mussels, either by reintroducing them or improving water quality.

“It’s not as like these guys are total goners,” she said.



-- Andrew Theen

atheen@oregonian.com

503-294-4026

@andrewtheen