To determine the extent of this decline, biologists with the Florida Museum of Natural History, Florida Fish and Wildlife Conservation Commission, Georgia Department of Natural Resources and the U.S. Geological Survey pored over museum specimen data to establish how widespread the species had once been.

The designation of critical habitat means that any federal agency – or state agency using federal funds – needs to comply with a set of standards when working in and around the mussel environments.

Many ‘kidneys of the river’ are endangered

Freshwater mussels play an indispensable role as water purifiers in streams and rivers, filtering out organic debris and excess nutrients and providing a source of food for fish, turtles and a variety of mammals.

Although mussels can be found worldwide, North America boasts the highest diversity of freshwater mussels on Earth, with over 300 species that are mostly concentrated in the Southeast U.S.

Yet their diversity belies an extinction crisis that has been silently building over the past century. Freshwater mussels are considered among the most endangered animals in the U.S., with 70% of species at risk of extinction due to the long-term effects of pollution and development.

Biologists were unable to locate even a single individual between 1994 and 2008, despite spending countless hours searching streambeds and river channels, prompting fears the Suwannee moccasinshell had gone extinct.

“They’re not very easy to find, and if you see more than three individuals per site, you get really excited,” Williams said.

Looking for mussels in the Suwannee can be an especially time-consuming task because many of them burrow into the river’s sandy bottom. To find them, biologists have to slowly sift through sediment by hand.

Pursifull and biologists from the Florida Museum, Florida Fish and Wildlife Conservation Commission and Georgia Department of Natural Resources conducted aquatic surveys in 2014 and 2015. They looked extensively in places where museum specimens had been collected previously and in habitats where the species could occur.

In Florida, researchers were unable to find any Suwannee moccasinshells in many regions where they’d formerly occurred, including the lower Suwannee River and the upper reaches of the Santa Fe. They were also absent in the Withlacoochee River, meaning they may have entirely disappeared from Georgia, in total marking a 67% decline in their former range.

They’re now primarily restricted to a small stretch of the Suwannee River, where a network of springs helps regulate water temperature and dilute pollutants. Yet even here, state and federal biologists could only dredge up 73 individuals thinly spread across 75 miles of streambed.

Threatened by pollution, environmental change

The decline of freshwater mussels is due to several interconnected causes. Their role as water purifiers makes them extremely sensitive to pollution. Sewage spills from treatment plants are a common occurrence in the lower Withlacoochee, for example, where almost no moccasinshells remain. The spills can release millions of gallons of raw waste, which has a cascade of negative effects on the environment. The ammonia in human waste is particularly toxic to aquatic fish, mussels and other invertebrate life, Williams said.

“The Suwannee Basin has a problem with fertilizers coming in, probably more so through the springs than anything, because the geology of that area is like Swiss cheese,” Pursifull said….

When a pregnant female is ready to release her larvae, she signals to unsuspecting fish nearby with an intricate lure disguised as food.

While some mussels are seemingly able to stow away on just about any fish that comes along, others are restricted to just one or two species. The Suwannee moccasinshell primarily relies on brown and blackbanded darters to get around, fish that don’t typically travel far. This likely inhibits the ability of these mussels to easily recover from rapid environmental degradation, Williams said.

Increased water runoff due to urbanization also reduces visibility in streams and rivers by adding suspended soils and kicking up sediment, making it harder for fish to find mussel lures. “If you have sediment in the water, and the water is cloudy, that means all the visual cues are gone,” Williams said.

Despite the odds, biologists remain hopeful that the protections conferred by the critical habitat designation may act as a catalyst in spurring conservation and population growth for the Suwannee moccasinshell.

“Agencies will now be required to consult with us to ensure that their project does not adversely modify or destroy critical habitat,” Pursifull said.

Any project that receives federal funding or permits is subject to the rule. In and around rivers, these most often include the construction of new bridges and landscape renovation carried out by state departments of transportation and dredge and fill permits issued by the U.S. Army Corps of Engineers.