Counting Darters

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John Fleischman

Audubon:July/August 1996

The Little River comes tumbling cold and clear out of the Great Smoky Mountains and rushes northwest toward the U.S. 411 bridge, where David Etnier and generations of his University of Tennessee zoology students have waded waist deep into the rushing water to seine for darters. There being no better introduction to the fish or the river, I drive down to Knoxville to plunge in.

Etnier brings students and visitors to the Little River to see darters, a bottom-dwelling, current-loving perch. Darters are set apart from other perches by their minimal or absent swim bladders. That gives them a slight negative buoyancy that enables them to sit on the bottom, balanced on a tripod of two front fins and the tail. From this stance, they dart out to take their prey or to avoid becoming prey themselves.

In human eyes, darters are very small. Even anglers sometimes lump darters in with minnows and chubs as undistinguished live bait. But darters are large in other dimensions. They are bewilderingly diverse--150 currently recognized species--and nearly all of them are astoundingly colorful, especially in spawning season, when their tiny bodies are flecked, striped, and banded in iridescent hues that make a rainbow trout look homely. They are fish with pizzazz. Even their names are a wonder:greenbreast, greenside, tessellated, fantail, orangefin, glassy, spottail, Tippecanoe, variegated, duskytail, harlequin, and on and on.

Most people know only one darter, Percina tanasi, the snail darter. Etnier is the man who made the snail darter famous, discovering what was then a new fish to science in 1973, just upstream of the all-but-complete Tellico Dam, which was being built by the Tennessee Valley Authority (TVA). Awarded federal endangered-species status in 1975, the snail darter became the unofficial plaintiff in a lawsuit that went all the way to the Supreme Court, a 1978 case largely remembered as "the little fish versus the big dam." The little fish won the suit. The big dam won the day.

Only John Travolta took more abuse in the '70s than the snail darter. Its smallness offended people. "The awful beast is back," wailed Senator Howard Baker of Tennessee, "... the bane of my existence, the nemesis of my golden years, the bold perverter of the Endangered Species Act is back." Arguing against the snail darter before the Supreme Court, Attorney General Griffin Bell handed the justices a pickled specimen to point out that adults run only two and a half inches in length. Unfortunately for Bell, Congress had failed to set a minimum keeper size for endangered species.

Still, a fish too small to eat can make a tasty political morsel. In TV sound bites, the snail darter became a symbol of nature's unseemly arrogance. Here was a stupid little fish, for heaven's sake, standing selfishly in the way of the TVA's beautiful dam. If only it would listen to reason and go quietly extinct. Then the Supreme Court ruled for the snail darter in Hill v. TVA, a broadly written six-to-three decision that certain conservative legal scholars still call infamous.

If it was infamous, that was because both sides won and both sides lost. The Endangered Species Act (ESA) was upheld, but the Supreme Court did not save the snail darter. It saved itself, turning up two years later in David Etnier's net in South Chickamauga Creek, 60 miles away. Through legislative chicanery and political clout, Senator Baker rammed an ESA exemption to finish Tellico through Congress and across President Jimmy Carter's desk.

But I had not driven down to Knoxville just to rehash the 20-year-old snail darter affair. The political battle over the Endangered Species Act now has moved on, and so has environmental science. Yet those "awful beasts:the "perverted" darters, may be back to haunt judges, and ecologists.

This time the issue is not a single endangered species but the breakdown of a whole group of animals. Taken as group, the highly diverse darters are showing an alarming rate of endangerment. Taken as a group, the same can be said of North American freshwater fish. Indeed, the same can be said of North American frogs or Pacific island birds or many other highly diverse but highly threatened groupings of organisms around the world.

In its starkest terms, the question is whether the earth is in the throes of "a mass-extinction event," an epic winnowing of life-forms similar to the collapse of the dinosaurs 66 million years ago, at the end of the Cretaceous period. Judging the pace of worldwide extinctions, though, is difficult. One promising avenue is to analyze entire taxonomic groups of animals or plants, looking for high rates of extinction. The most vulnerable seem to be those with high numbers of endemic species, organisms that exist in one place and nowhere else on earth.

That's where the darters come in. With 150 species to choose from, darters are prime examples of endemism. Some have wide ranges, but others are found only in a single river drainage, on one side of a continental divide, in a particular spring, or in a certain reach of river with a certain substrate.

Taxonomically, the darters are a tribe, three (or possibly four) distinct genera, according to Lawrence Page, an ichthyologist with the Illinois Natural History Survey. Darters are found from the Atlantic-slope drainage to the Ozark Mountains, from Canada's southern Yukon Territory to Mexico, where, says Page, a single species near Durango is the only native darter on the Pacific slope. But the center of darter biodiversity is the southern Appalachian highlands.

Down in Tennessee, at the epicenter of this center, David Etnier says that some darter species are doing well and others are hanging by a thread. But as a tribe, he says, the darters of the southeastern United States exhibit an inordinately high rate of "imperilment." He uses the term in place of the legalistic endangered or threatened. It comes to the same thing. In a 1996 survey of the freshwater fish of the Southeast, Etnier concluded that 91 of the region's 490 species are imperiled. It's a regional study but a telling one. The Southeast is especially "speciose" because of its postglacial geology, mild climate, and complex hydrology. North America has about 950 fish species; the Southeast has local populations of half. Nineteen percent of the region's freshwater fish species are in trouble, according to Etnier.

That's a distressingly large block. When Etnier analyzed southeastern fishes by families, three jumped out with extremely high rates of imperilment--sturgeons, catfish, and perches. An ancient family, sturgeons have relatively few species, and with five of the six southeastern species jeopardized, they had the highest imperilment rate. The imperiled catfish all belong to a subgroup called the madtoms with 8 species of 31, or 26 percent, imperiled. The largest family, the perches, with 149 species, had the greatest number imperiled, 46 species, or 31 percent of all perch. The 46 jeopardized perches were all darters.

That makes the darters of North America a potential extinction hot spot, part of a global pattern. Charting these hot spots is providing some of the strongest evidence so far that current extinction rates are well above "normal" background rates, which are derived from fossil studies. Many modern extinction centers are well known--Hawaiian birds, Polynesian snails, Australian mammals. But extinctions, of course, are not restricted to islands or to distant lands. One of the most frightening examples is the freshwater mussels of North America. In one order, the Umonoida, 35 of 300 native species are already extinct and another 120 are severely threatened. That's half of an entire taxonomic order. It puts them "on the brink of a major and widespread extinction event" according to Arthur Bogan, a leading mussel expert.

No one is saying that darters are close to a taxonomic collapse of that magnitude, but their vulnerability is plain. The problem is that they evolved over millions of years into animals beautifully adapted for life in clear running water--and free-flowing, medium-size rivers without heavy siltation are becoming one of the rarest habitats in North America.

That's what brings me to Knoxville and Dr. Etnier. On a raw March morning, he's heading for the U.S. 411 bridge, east of Maryville, to collect a longhead darter. Although he normally counts and releases rare species, Etnier has a student in Illinois in need of a longhead darter specimen for a molecular study of its DNA. But Etnier also scouts the Little River for fresh signs of bulldozers, chainsaws, and unfenced cattle. They are the agents of erosion that will dump even more silt into Tennessee's already burdened medium-size rivers. Siltation is the greatest peril to fish reproduction in the Little River, he tells me as we roll along in his van, a combination zoological lab and fisherman's shack on wheels; rods, collection bottles, rain gear, and flattened aluminum cans slosh around underfoot. Somewhere in the flotsam is an extra pair of canvas waders for me. Outside the window, I watch heavy thunderstorms roll along the dark face of the Smokies.

To go seining, we need another pair of hands. Our volunteer in the back seat is Gerry Dinkins, a former graduate student of Etnier's who now works as a private environmental consultant. I quickly realize that I am a happy excuse for these two--the professor and his former student--to go counting darters or any kind of fish, insect, or bird. Etnier and Dinkins play taxonomy the way some people play tennis--cutthroat. For 12 years they've been engaged in a two-man bird-spotting competition that has clearly gotten out of hand. The contest runs from New "Year's Day to New Year's Day, Dinkins explains. The prize is a bottle of Wild Turkey and bragging rights. Dinkins has won twice, Etnier all the other years, and Dinkins figures he'll need at least 220 bird species to be competitive this year. "With the escalation we've had lately" Etnier says with a gleeful smile, "you're going to have to have three hundred species to win soon.

What warblers are to songbirds, Etnier tells me, darters are to fish--endlessly colorful and endlessly varied. To see them in the wild and to know them by sight is a challenge for the well-trained eye. Just how well an eye can be trained becomes clear once we finally wade into the Little River. Dinkins carries the seine, a weighted nylon mesh about eight feet across and five feet high, slung between two stout timbers. The idea is to plant the poles angled back in the current so the net's bottom edge stays taut against the substrate. Give a darter the gap of an inch under a net and he's gone.

This is the theory. In practice, I can barely walk in my waders and nearly topple full length into the water. Dinkins gingerly unfurls the seine. Push your end down like this, he says, demonstrating. The white nylon balloons out in the current. A few yards upstream, Etnier starts kicking, advancing towards us in a wild Tennessee water stomp--kick left, shuffle, kick right, shuffle--to flip over the slabs and boulders where darters lurk. The current is so fast and Etnier's turmoil so great that I see nothing go into the net but leaves and mud. Yet when we hoist it up, the mesh is crawling with life--stone rollers, mayflies, crane fly larvae, minnows, sculpins, and, of course, darters. Etnier's fingers fly through the catch, instantly sorting out the darters. Huddled over the mesh, he and Dinkins toss names back and forth--blennioides, jessiae, rufilineatum, some very young vulneratum, but no macrocephala. They are unhappy about that. For my benefit, Etnier fumbles for the common names--greenside darter, blueside darter, redline darter, the little wounded darters, but no longhead darter. Etnier longs for a macrocephala.

We trundle the seine into deeper water, wading cautiously across a channel to try our luck behind a sandbar. Then we backtrack into rocky shallows. Etnier reads the river the way the darters do, sorting out the habitat by the swiftness of the current, the depth, the coarseness of the sediment, the gauge of the boulders and gravel, even the shape of specific stones. Almost under the bank, we duck under branches to cast the net.

We haul up leaves, bugs, and darters. Here is a male Tennessee snubnose, Etheostoma simoterum, Etnier says. A real beauty. Look at his snout, he says, holding the darter up on his wet palm. See how it's short, barrellike. I look more closely at his distinctive snout and at his iridescent sides, already coloring up nicely for the spawning season, and for a moment I can see the difference between him and all other darters--his snubnose hood, as it were. Then Etnier pops the snubnose back into Little River, where he becomes just another little fish.

The darter experts are also concerned (and arguing among themselves) about whether the first modern extinction among the tribe has just occurred. A darter species has gone missing:the Maryland darter, Etheostoma sellare. A rarity among rarities, the Maryland darter is an Atlantic-slope species first identified in 1912 and not found again in the wild until 1962. Only in 1965 did zoologists snorkeling Deer Creek, a small tributary of the lower Susquehanna River in Maryland, locate a small population. Its rarity earned sellare an immediate place on the federal endangered-species list. In 1986 Rich Raesly, a biologist now at Maryland's Frostburg State University, went snorkeling in Deer Creek to redocument the Maryland darter. For the next two years, he saw sellare at this one location. In 1989, he couldn't find them. Raeslv looked again in 1990 and every year since. Is sellare extinct? Proving a negative is difficult. Just because a species is not where it used to be doesn't mean it isn't somewhere else. After the TVA finally dosed the floodgates at Tellico, the snail darter was supposedly extinct--until Etnier found tanasi living in three other Tennessee creeks. By 1984 Etnier felt comfortable enough to recommend lowering the snail darter's status from endangered to threatened.

Etnier believes there is a chance that a reserve population of sellare may be found in the Susquehanna itself. Unfortunately, the lower Susquehanna, just before it reaches the Chesapeake Bay, is no mountain stream. It is wide, turbid, and rocky. Conventional means of searching--seine, scuba, electroshock--wouldn't work. Etnier wants to use sodium cyanide, a highly localized and short-lived poison that would force the darters to the surface, where they could be scooped up, quickly counted, and returned to the water unharmed. Etnier says he's used the method in Tennessee streams for years without losing a fish. Raesly has applied to the U.S. Fish and Wildlife Service for permission. But approval for anything involving the Chesapeake Bay, cyanide, and a federally endangered species in the same sentence could take time.

Losing sellare would be a blow. It would certainly demonstrate the perils of endemism. "Of all the freshwater fishes in North America" says Raesly, "this one has one of the most restricted distributions." Even adding the lower Susquehanna, the Maryland darter's entire geographic range is only a few square miles. That makes sellare doubly interesting to Raesly. "It belongs to a subgenus in which all the other members occur in the Mississippi River drainage" he says. "Here you've got this one species way over here in the Atlantic slope, very much isolated from members of its group. From a zoogeography point of view and also from an evolutionary-biology point of view, that poses a really interesting question:Why is it over here all by itself?"

Which may be another way of asking, Why are there so many darters at all? It is an axiom of modern phylogenetic biology that all members of a taxonomic group derive from a common evolutionary ancestor. As they diverge from one another, they are divided cladistically into families, genera, and species. The darters are an exuberant demonstration of the possibilities of divergence.

I find that out while looking under a rock at a male Etheostoma percnurum, the duskytail darter. He is looking out at me through the glass wall of an aquarium in an out-of-the-way strip mall in suburban Knoxville. After giving up on finding a longhead darter in the Little River, Etnier has brought me here to see the world headquarters of Conservation Fisheries, a nonprofit, state-of-the-art hatchery for imperiled little fish, notably madtoms, dace, and darters. It's also seat-of-the-pants science, the creation of three former Etnier students, J.R. and Peggy Shute and Pat Rakes. They rely on federal and state grants just to keep their no-frills operation going, and they all have other jobs so they can eat regularly. Without mixing the genes of subpopulations, the idea is to make endemics a trifle less endemic by raising rare fish to recolonize their historic ranges. When we arrive, J.R. apologizes for the temperature inside. On this brisk day, the windows are open and fans are blasting to get ready for spawning season. There is ice indoors on the madtoms' pool.

The partners have constructed an amazing tangle of pumps, sumps, glass tanks, filters, and ultraviolet sterilizers patched together by plastic rain gutters. Here they puzzle out the secret sex lives of rare fish, discovering, for example, that spawning in the blackside dace is triggered by a pheromone released by a nest-building minnow. With the aquariums rerigged so the minnows are "upstream" the dace respond as they have for thousands of years.

The male duskytail darter pursues a different course. J.R. points him out under his nesting base, a slate with two inches of swimming room under one edge. If you look at the top of his head, J.R. tells me, you can see what look like little balls. They are pseudo eggs, a seasonal swelling of the male's dorsal fin. To passing duskytail females, the pseudo eggs make him look like a good father, or at least a promising mate, a male with a viable nest and the perseverance to guard it. In this way, the male duskytail recruits females for two or three spawnings. It makes good genetic sense, but it seems, on first hearing, so unlikely a reproductive strategy that I am humbled by the creature that perfected it.

I tell myself that evolution is supposed to be blind to all purposes but survival. Yet the darters--all 150 kinds--remind me of a musical composition, a theme and variations. I imagine a supernatural J.S. Bach "composing" fish species like a fugue. It's as if the genius of the darter tribe was to demonstrate the possibilities within a single strand of life-forms. I know that darters intend nothing more than making more darters, but it seems that to lose one, two, or a dozen or more darter species is to break the set, destroying not a work of art but a work of life.