Freshwater Mussels: Endangered but Coming Back
Listen Now“Find one?”Biologist Fritz Vorsek pops out of the stream and lifts up his mask and snorkel. He’s spotted a rather small mussel nestled in the stream bed. He trudges toward the bank to hand it to fellow department of fish and wildlife biologist Monte McGregor, who will give it a closer look. They’re combing a section of stream in the upper Cumberland river system for an endangered mussel species called the Cumberland Bean. It’s a black, bean-shaped mussel that could easily fit in the center of the palm of your hand. They’re trying to find pregnant….or gravid in the mollusk world…females. And they’re finding anything but.“I’ve got four females of the Painted Creek Shell and four females of the Rainbow mussels that are gravid that I’ll be taking back and doing some work with them as well.”McGregor kneels near the bank, sorting through a small pile of mussels the two have found. Some he’ll take back to his lab and others he’ll replant in the stream. Last year, they tagged Cumberland Bean females with a little magnetic sticker and plopped them back in the water. Today they’ve come back with a kind of aquatic metal detector to try to pick up their signals. But the search has turned up little.“It’s not good seeing all the dead animals here. That’s kind of alarming. We’re not sure why they’re dying. Again, they’re very sensitive animals.”Sensitive, that is, to environmental stresses. A sizeable mussel population can tell you a lot about the health of that river or stream. Mussels filter water through little muscular tubes to feed on algae and bacteria. One mussel can filter many gallons a day. That keeps the water clean. But it also makes mussels little underwater “canaries in the coal mine.” They’re the first to die when water quality declines. And two key factors have damaged water quality in the state.
That’s why McGregor is trying to raise endangered mussels in captivity. Returning them to the wild and encouraging new populations would help Kentucky waterways. But he must battle pollution. And especially dams. US Fish and Wildlife Service mussel biologist Bob Butler works out of his North Carolina office to bring endangered mussels back from the brink. He blames dams for most of that endangerment.”When you put a dam in you change a running water environment to a standing water environment. And it starts to fill up with sediment.”And that destroys the rich mixture of gravel and sand and pebbles mussels love to nestle in. And it makes it tougher for them to feed on their preferred diet of algae and bacteria because of all the other particles clouding the water. They starve to death.But it also makes it harder to breed. Mussels develop a clutch of microscopic eggs inside their shells. Then they wait for the right fish to come along. This is the fish that will host their brood in its gills for a little while, unaware that hundreds of little mussel eggs are nourishing themselves in its fish blood. Each mussel species, it seems, prefers its own species of fish. And biologist Bob Butler says dams have affected those fish populations too.“The fish host for most of these mussels are small benthic species like darters and sculpins, maybe catfish and some shiners, that also need running water to survive. So the fish communities change, the mussel communities change when you put dams in.”Coaxing those communities back is no easy task.Welcome to McGregor’s mussel nursery, just a few miles outside downtown Frankfort.In a room full of gurgling tanks and plastic tubes, two scientists are huddled over a Petri dish with a long eye-dropper and a bucket of woozy fish. McGregor says the barely visible specks in that Petri dish are the result of third trip to the river that netted a bit more success.“Those little specks are several thousand of that Cumberland Bean mussel we went looking for. And what he’s doing is, he’s put the fish to sleep a little bit with an anesthetic. And he’s actually squirting them right on the gills. This way we know for sure. When you’re working with an endangered mussel you want to take advantage of every larvae.”Until recently, scientists didn’t know which fish each mussel preferred. It’s taken educated guessing and trial and error to find out. It’s also only in the last few years that scientists have learned what to feed these babies. McGregor and his staff are still figuring out the recipes in this, the mussels’ own personal kitchen. Algae is the main ingredient. But getting the mixture just right requires experimentation. And experiments are bubbling up through dozens of tanks and tubes, including a giant cylinder next to McGregor. It holds a disturbing fluorescent green liquid that’s on its way to becoming the kind of dark green sludge mussels salivate over.“So you can see the progression from light green to dark green to very dark green we’ll be harvesting. This procedure has taken a few years to develop how the proper way to getting the right algae for the right mussel.”More recent developments may allow McGregor to rear some mussel eggs right in the lab, without a host fish. Hundreds of eggs are put in a dish with a chemical stew of amino acids and vitamins and minerals. If the mix is just right, they grow up. But until the last few years, scientists had little success.”The technique was developed in the early 80s, but really there have only been a few people who have tried to work it out. ”McGregor says the process is working, but he wants to try it out on more species. With so many steps involved in breeding and raising mussels, it seems that recovering any of the endangered species could take forever. But McGregor says otherwise.”So in my lifetime, can we? Yes. I think we have a better chance of getting a species maybe off he endangered species list. But again, you know, it takes a lot of time. Multiple years of raising animals, putting them back, and getting new populations established.”McGregor acknowledges that he can only hope to establish new populations in healthy streams and rivers. In Kentucky, the federal government recognizes more than a thousand miles of waterways as “impaired,” or not so healthy.