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The Delightful and Doomed Mollusks Among Us

In the American West, freshwater mussels are in broad decline. These species are silent and strange, unseen and mostly unknown — so why should you care?

By Jimmy Tobias


(Photo: Wikimedia Commons)

During a long weekend last August, a friend and I got together for a low-budget bachelor party and went fishing near Missoula, Montana. I won’t tell you where exactly — the spot is too good, too unspoiled, to share. It’s a remote canyon boxed in by thick pine forests and mountain walls, punctuated here and there with crumbling boulders and cold clean streams. As we drove in, a black bear lumbered across the road to welcome us. The trout were tough and hungry. Osprey drifted overhead. In the river, you could see the first of the salmon returning to spawn and die. And, after wading into the cool water one warm afternoon, I discovered another rare and beautiful surprise — at my feet, scattered like jewels in crevices and eddies and pools, a sprawling bed of freshwater mussels surrounded me on all sides.

Since then, mussels have been on my mind — I find mollusks in general, with their complicated lifecycles, glistening shells, and gooey bodies, strangely fascinating. The freshwater varieties, passing their long lives tucked away in unassuming creeks and rivers across the country, are particularly alluring. But I’d never before in my life laid eyes on them, and I soon discovered why.

The freshwater mussels of the American West are in broad decline. This fall the Xerces Society, a leader in invertebrate conservation, submitted assessments to the International Union for Conservation of Nature’s Red List seeking official recognition of the dangerous decimation of these species, including the western pearlshell mussels I stumbled upon in August. Rising water temperatures, invasive flora and fauna, and the decline of host fish like salmon, according to researchers, are all conspiring against the creatures. We’re living through the sixth great extinction, and this is one of its most appalling aspects: These days, when you encounter an animal for the first time, it is reasonable to ask whether it, like so many other species, is inching toward disappearance too.

Wildlife biologist Dave Stagliano has spent years studying the freshwater mussels of Montana. He knows them. He admires them. And, more than anyone else in the state, he’s watched the rapid retrenchment of their once-ample range.

“In the last decade there have been significant declines,” he says. “Between 2004 and 2014, I documented about 40 populations that blinkered out.” More than a quarter of Montana’s pearlshell mussel populations, he explains, have disappeared in just 10 years.

The situation is no better in the American Southwest, and particularly in California, where Jeanette Howard, a research scientist with the Nature Conservancy, has kept tabs on freshwater mussels for years.

A recent survey of 75 historical freshwater mussels sites across California, Howard explains, revealed that only about 50 percent of those rivers streams or lakes still contained living mussels — at low densities. In southern California, meanwhile, mussels have been almost completely extirpated from freshwater systems. “It’s a little disturbing,” she says.

These case studies are symptomatic of creeping extinction, and the Xerces Society wants everyone to know it. The assessments it sent to the IUCN document the steady demise of three freshwater mussel species in the West: the winged floater, the western ridged mussel, and the western pearlshell. According to the Society’s crowdsourced digital database of museum records, scientific research, and field observations, these species have disappeared from between 17 and 43 percent of their historic watershed habitats since people began keeping records more than 100 years ago. And, as the research of Stagliano, Howard, and others indicates, the pace of disappearances during the last decade has been particularly alarming. The Xerces Society has thus asked the IUCN to formally list these species as either vulnerable to extinction or near threatened.

Freshwater mussel populations are wild nature’s water filters, capable of removing sediments, heavy metals, and other contaminants from millions of gallons of water each day.

“If there is any chance we can avoid further decline or loss, the only way that can happen is if people are looking for causes and trying to mitigate against them,” says Emilie Blevins, a conservation biologist at the Xerces Society. “The [IUCN] Red List serves as a jumping off point for agencies to consider whether mussels are at serious risk in their areas.”

The Society is focused on Western mussel species because less than a dozen live on the arid side of the Mississippi and they are little understood. In the Eastern United States, meanwhile, there are hundreds of freshwater mussel varieties. Many of these are also suffering — dozens of them, in fact, have already gone extinct — but they tend to be better studied and garner more public resources than their Western brethren.

The great extinction event underway today forces us to confront, to study and understand, the creatures we are killing. To decipher how and why Western freshwater mussels are dying in droves, for instance, one must first know something about the fascinating lives they lead. North America is home to more than a third of the world’s freshwater mussel species. These animals can live for 80 years and more, buried in sediment and barely moving, and some today have been alive since Dwight Eisenhower was in the White House. They are fecund, able to generate millions of larva during reproduction. In the early stages of their lives, they even briefly become parasites, attaching to host fish like salmon and native trout to better disperse throughout the watershed.

This last characteristic of bivalve life, magical though it is, represents a gap in the evolutionary armor. Because Western freshwater mussels rely on native fish for dispersal, the displacement of salmon and native trout due to dam building and invasive species, among other causes, has proven a major factor in mussel decline. “Without the fish,” Stagliano says, “[the mussels] are not going to reproduce.”

Other contributors to mass mussel death include contamination from mining and agricultural waste, shoreline development, warming water temperatures, channelization of streambeds, and water withdrawal from creeks and streams for irrigation purposes, according to the Xerces Society’s IUCN assessments.

Mussel extirpation will likely continue, causing little concern among the environmental community, much less the general population. That’s the trouble with species that are not a major food source, are not well known, are not big and beautiful and human-like in action or appearance. Freshwater mussels are weird and silent and unseen. So why should anyone give a damn if our rivers are denuded of their bivalve inhabitants?

A few reasons: Freshwater mussel populations are wild nature’s water filters, capable of removing sediments, heavy metals, and other contaminants from millions of gallons of water each day. They also provide a stable food source for wildlife of all sorts, from raccoons to otters to bears. And they were once a key element of indigenous food economies and ceremonial cultures too.

But if that litany doesn’t incite interest, if it isn’t enough to spur more state and federal funding for mussel research and restoration, including stocking programs in places where mussels are still viable, then perhaps the big picture will do the trick. The loss of these mussels is part of a larger diminishment. It is one chapter in an epic story of impoverishment afflicting freshwater ecosystems across the country and the world.

The freshwater biodiversity crisis is real, and it has been unfolding for decades. In 2005, in a report in Biological Reviews, an international group of ecologists and biologists offered this scary assessment:

Fresh waters are experiencing declines in biodiversity far greater than those in the most affected terrestrial ecosystems, and if trends in human demands for water remain unaltered and species losses continue at current rates, the opportunity to conserve much of the remaining biodiversity in fresh water will vanish before the … decade ends in 2015.

It’s 2016 and things have not improved, according to Jeanette Howard, the mussel researcher in California. Rather than canaries in coal mines, mussels in the Missouri, the Mississippi, and more are warning us with their mortality that freshwater biodiversity is in bad shape. With a note of mourning in her voice, Howard calls the condition of freshwater ecosystems today, and especially in the West, “grim.”