Lowly mussels bond with salmon: Oft-neglected species may help clean rivers, bolster fish runs
By: Steve Law, Portland Tribune August 18, 2011
Not so long ago, freshwater mussels were largely unloved, unstudied and unprotected. They’re easy to overlook, resembling small black rocks with slits. They’re not tasty to the human palate, unlike marine mussels. Ironically, they were so unappreciated that maintenance crews sometimes crushed them while doing in-stream work to benefit salmon.
Now Portland’s nonprofit Xerces Society for Invertebrate Conservation is spreading the word of how this incredible species is intimately linked with salmon — and may be a key to restoring salmon runs.
It’s no coincidence that freshwater mussel beds often are found where there are healthy salmon runs, says Scott Black, Xerces Society executive director, while wading out to Johnson Creek one July morning to document the number of western pearlshell mussels.
“What benefits the mussels benefits the salmon, and what benefits the salmon benefits the mussels,” says Celeste Mazzacano, aquatic program director for the Portland-based conservation group.
One freshwater mussel can filter up to 18 gallons of river water a day. “When they live in a dense bed, they can play a significant role in purifying the water,” says Sarina Jepsen, Xerces Society endangered species program director.
Western pearlshells, or Margaritifera falcata, can live for a century or more, among the longest living species on Earth. The closely related M. margaritifera can live nearly 200 years.
Biologists determine the age of freshwater mussels by counting the rings on their shells, much like rings on an old-growth tree.
Scientists can even gauge historical stream conditions via close analysis of the shells, says Robin Jenkinson, restoration coordinator for the Johnson Creek Watershed Council.
Some biologists liken the freshwater mussel to a “canary in the coal mine,”an indicator species that reveals the health of rivers.
Mutual dependence The kinship between freshwater mussels and salmon runs both ways. Mussel shells provide a mini habitat for midges, mayflies and snails, which provide food for salmon.
Salmon and trout, in turn, provide habitat for newborn mussel larvae. The western pearlshell, one of the most common species in Oregon, releases microscopic larvae, called glochidia, into the water. Fish bite them, and the glochidia clamp onto the fins or gill filaments of the fish. In this way, wannabe freshwater mussels hitchhike for several days or even months on a host fish. When ready, the glochidia release themselves and burrow into the riverbed sediment, populating new waters with freshwater mussels.
A variety of community groups and government agencies are working to improve conditions in Johnson Creek, which flows 25 miles from the Cascade Range foothills to the Willamette River, through Gresham, Portland and Milwaukie.
Last December, four adult salmon were spotted on Johnson Creek in Gresham, the farthest upstream they’ve been seen for many years. Perhaps not coincidentally, beds of western pearlshells have been spotted in Johnson Creek in Gresham, near the confluence of Sunshine Creek. The beds are in a 5.6-acre parcel near Telford Road acquired by Metro in early 2010, with money from a 2006 natural areas bond measure approved by voters.
On a recent visit to the beds near Sunshine Creek, Mazzacano found some mussels she figures are five to 10 years old, a positive sign of new populations.
Biologists are trying to get a handle on how many freshwater mussels live in Johnson Creek, to establish a baseline for future analysis of how the species is faring.
Species in decline Freshwater mussels don’t get the attention of more glamorous species, but they’re in serious decline. Nearly three-fourths of the 297 native freshwater mussel species in North America are imperiled, according to the Xerces Society, and 35 species are thought to have gone extinct in the last century.
Despite being one of the most endangered groups of animals on Earth, surprisingly little is known about mussels as a whole.
The Lewis and Clark journals refer to a mussel shoals area of the Columbia River, a sign they once were common, Jepsen says. They’ve since largely disappeared from the Columbia, as well as the Middle Snake River in Idaho, and the Umatilla River, where they were historically part of the diet of the Umatilla tribes.
“It was a source of protein when there wasn’t a lot of protein around,” Mazzacano says.
Xerces, a Portland-based group with a global mission to study and conserve butterflies and other invertebrates, convened a network of scientists into a study group several years ago, to share their knowledge and observations about freshwater mussels.
One of Xerces’ roles is to take what scientists know and help educate land managers, Black says. In 2009, the group published a 50-page booklet, “Freshwater Mussels of the Pacific Northwest.”
A few years ago, the Oregon Department of Fish and Wildlife enacted protections for the species, Jepsen says. Now when crews remove culverts, alter river flows or undertake other in-stream projects, they take pains to avoid crushing freshwater mussels on the creekbeds.
The new Metro parcel is not far from an area considered ripe for future development, Jenkinson says. So biologists hope to identify important habitat, and establish a baseline of the mussels’ population and health, to properly assess how it is faring in the future.
Counting shells Xerces, along with partner groups like the Johnson Creek Watershed Council, is training volunteers to conduct surveys of the mussels, to establish a broader database of the state of the species here.
Biologists from the two organizations fanned out on a recent July morning on a stretch of Johnson Creek near the Cedar Crossing covered bridge, in East Portland. The mussel population has never been surveyed there, Jenkinson says.
The biologists peer into aquascopes, tubes of PVC pipe with a viewing glass, on the surface of the creek, jotting down what they find in segments of the creek called transects. Jenkinson spots shells of dead (invasive) Asian clams, sculpin and abundant crawdads, but no mussels.
By midday, no freshwater mussels are observed.
Mazzacano speculates that huge stones of rip rap lining the riverbank, laid in the 1930s by Works Progress Administration workers, allows water to shoot through at high velocity, washing out young mussels and preventing them from becoming established on the riverbed.
So far, there are no plans to move freshwater mussels to repopulate an area, or to use them to improve river quality. Xerces has ethical concerns and fears about introducing new diseases, Jepsen says.
Johnson Creek was once known as an albatross, the urban stream that perennially flooded homes built on its banks. But a variety of restoration efforts have vastly improved the creek.
It’s an ideal place to educate school children and other urban dwellers about the ecology and importance of streams, Jenkinson says.
New survey data on freshwater mussels will be added to previous studies on birds, fish and other river conditions. “It’s just one more piece of the puzzle” to improve the health of the creek, she says.