The Boulder Darter: a Conservation Challenge

The Boulder Darter: A Conservation Challenge Noel M. Burkhead and James D. Williams ' The boulder darter (Etheostoma wapiti) is a small-sized member of the perch fam- ily. In general, darters are a diverse group of bottom-dwelling fishes (about 140 species in the United States) that typically flourish in clean, flowing creeks and riv- ers. Unfortunately, when darters are brought to the attention of the public, the news too frequently is about the decline or demise of a species. Such is the case for this small fish. The boulder darter was listed by the Fish and Wildlife Service as an Endan- gered species in 1988. Its only surviving population is found in the Elk River, a large tributary system of the Tennessee River in southern Tennessee and northern Alabama. The primary reasons it needed listing protection were its reduced distribution and the vulnerability of its This male boulder is guarding its nest site. The eggs are present at the right margin of the remaining habitat. The boulder darter is nest cavity. currently restricted to about 63 miles Ford Dam from warm to cold water; im- (101 kilometers) of the main channel of The loss of biological adaptability in a species poundment of the lower Elk River by di- the lower Elk River and a few of its larger directly arises from the loss of its genetic tributaries. However, the species is not Wheeler Reservoir; fluctuating water lev- versity, which is a consequence of the species distributed continuously within this els from power generation at Tims Ford losing segments of its total population. Reservoir; industrial, municipal, and agri- The spotty occurrence of the boulder range, but is found at only six sites in the cultural pollution; and extensive siltation darter in the Elk River results in part main channel and three sites in two of from soil erosion. The primary reason from the rarity of its preferred habitat. As the tributaries. Historically, the boulder for the demise of the boulder darter in its common name suggests, the boulder darter also lived in Shoal Creek, a tributary of the Tennessee River in northern Shoal Creek was the impoundment of darter lives among boulders. However, it the lower creek by Wilson Reservoir, silt- Alabama, but that population has been is not found among boulders anywhere extirpated. ation from agricultural erosion, and pol- in the river bed; the location of the boul- lution from upstream municipalities in Extinction of the boulder darter may ders is important. The boulders must Alabama. Other populations of the boul- occur in water 2 to 4 feet (0.6 to 1.2 follow in the next 10 to 20 years unless some way can be found to increase the der darter probably existed in the Tennes- meters) in depth. Also, the boulders number and size of the populations that see River once but were extirpated by im- must occur in flowing water that is not poundments before they were detected. too swift, such as in riffles or rapids, and still survive. This fish shares some at- These powerfid forces degrading the Elk not too slow, as in slightly flowing pools. tributes with the Maryland darter River ecosystem have reduced the boulder Most of the Elk River between the (Etheostorna se/Lire,), a species that some experts now believe to be extinct. darter population to small, isolated subpopu- reaches affected by impoundment con- lations, an alarmingly fiimiliar pattern in sists of long, heavily silted pools that have southeastern rare fishes (some of which were little or no boulder substrate. .I-he rela- Reasons for Decline relatively common only 20 to 30 years ago). tivelv few riffles and runs are predomi- N lamy human-caused factors contrib- When the population of a species hcconìes nately floored with gravel and rubble sub- uted to the decline of the boulder darter. highly fragmented, the species loses its ability strates. At two of the six sites that harbor In the Elk River, the principal impacts to respond to the extremes of nature. For boulder darters, the boulders are in fact were impoundment of the upper river example, it may no longer be able to survive parts from old collapsed structures, a section by Tims Ford Reservoir; thermal extended periods of severe weather, disease, stone bridge and a spillway darn. [he alteration of the tailwaters below Tims or dramatic fluctuations in food sources. (0,1thated 11»1 4 ENDANGERED SPECIES TECHNICAL BULLETIN Vol. XVII Nos. 3-8 (1992) I Boulder Darter The artificial stream is a 4 by 8 foot gravel or a boulder and pieces of rubble, (,,,itinIfed fist)!!1 previous page) (1.2 by 2.4 m) plexiglass aquarium in although a space created between a boul- which current is generated by an electric der and bedrock might be acceptable; 2) survival of the boulder darter is amazing trolling motor. We mimicked important it must have a wedge-shaped configura- considering the rarity of its preferred aspects of the boulder darter's habitat in tion, with the two boulders touching at a habitat and the severe and chronic degra- the artificial stream, notably flow, tem- relative narrow angle, creating a space dation of the Elk River. perature. photoperiod, and substrate into which the female wedges her eggs; 3) composition. The boulder darters the site must have current flowing across spawned in May and June 1991, yielding it; 4) the cavity must be roughly horizon- Laboratory Observations the first observations of reproduction for tal (no vertical or nearly vertical spaces Biologists have long recognized the this Endangered species. What we were selected); and 5) the boulders must critical importance of knowing the repro- learned in this short period provided im- not only be in the correct depth and cur- ductive biology of an' imperiled species, portant insight into the inherent frailties rent ranges, but they must also occur in a especially for developing conservation of this darter at the critical point of creat- certain configuration relative to the cur- measures to protect and recover the spe- ing the next generation. rent and to each other. cies. Until recently, however, virtually The critical importance of current flow nothing was known about the life history across the nest space was revealed when of the boulder darter. Our first goal in Reproductive Habitat one trolling motor failed during a week- research on this species was to observe its The boulder darter spawns in the same end. All of the eggs in that nest died. spawning behavior and to identifY the habitat in which it normally lives: boulders Current is obviously important for oxy- area(s) of the river that served as spawn- in flowing water with a velocity of about 1 to genating the eggs and possibly for keep- ing habitat. Unfortunately, observing 2 feet (0.3 to 0.6 m) per second. The boul- ing the egg surface swept free of particu- boulder darter spawning behavior was der darter belongs to a reproductive guild of late debris and silt. This observation also not possible in the Elk River because of darters known as egg clusterers because the suggests that the persistent siltation of the the water's consistent turbidity. Further, eggs are laid in clusters in spaces beneath Elk River must be very limiting to the the river below 'Finis Ford Darn is subject rocks. The male darter remains at the nest survival of egg and possibly larval life to significant water level fluctuations re- site and aggressively guards the eggs against stages of the boulder darter. It is well sulting from power generation at the intruders. known that silt will smother fish eggs, darn. In order to overcome the obstacles The male boulder darter is picky about and species such as the boulder darter to studying the darter in its natural envi- the spaces he selects for nest cavities. In that spawn on the bottom are the most ronment, 10 darters were captured, trans- fact, the nesting sites must have specific vulnerable. ported to Gainesville. Florida, and placed attributes: I) the space MUSE be between A critical insight gleaned from these in an artificial stream. two boulders, not between a boulder and observations is that fluctuating water levels from power generation (2 to 3 feet changes in depth) must significantly alter the specific habitat features (depth and water velocity) of the nest cavity the male selected for spawning. It is quite possible that some boulder darter nests may be left stranded out of the water when water levels drop during periods of decreased power generation. Conversely, if a male spawned in a nest cavity during low water levels, how would the survival of the eggs be affected during high water levels? It is possible that fluctuating water levels may be reducing. perhaps significantly, the reproductive success of this Endangered species. What will be the fate of the boulder darter? At this time, we simply don't know. State and Federal agencies will work together and attempt to patch the An artificial stream was used to mimic important habitat features of the boulder darter. The (coutimied on ,gi ,. video camera was set up to record behavior. ' g 6; ENDANGERED SPECIES TECHNICAL BULLETIN Vol. XVII Nos. 3-8 (1992) 5 Boulder Darter (continued/Tom page 5i ecosystem wounds created by the hand of the human species. Perhaps some ways can be found to create new habitat. Arti- ficial propagation may also play an important role in the recovery of this imperiled fish. One thing is fairly certain: if nothing is done, the boulder darter. like the Maryland darter, will slip from the face of the earth.

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