The common name of Etheostoma chlorobranchium is the greenfin darter. It is one of the 324 fish species found in Tennessee

Tennessee

Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...

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Introduction

The purpose of this paper is to describe a practical monitoring plan for the Green-fin darter (Etheostoma Chlorobranchium). The geographical distribution of this species is primarily centered on mountainous streams and rivers in the upper Tennessee drainage region, from the Watauga River to the Hiwasee. Although little is known about the ecology of the green-fin, darters in general are important food sources for many fish. Freshwater eels commonly consume adult darters, and suckerfish prey upon their eggs. Spawning occurs primarily from may until august, and eggs are buried in the substrate. There is no active management plan for the species, and the species has yet to be evaluated by the IUCN. Most research specifically targeting E. Chlorobranchium has focused on gene introgression of the green-fin into populations of blue-breasted darter (E. Camurum), although this has not been shown to lead to any negative effects on green-fin populations. Because of its preference for specific microhabitats, such as fast flowing ripples, this species is particularly vulnerable to environmental disturbance. Furthermore, any population declines observed in the green-fin would more than likely trigger declines in other, larger fish, as they are a major source of food. It is therefore imperative that a this species is examined more closely, with an emphasis on discovering and avoiding potential anthropogenic disturbances.

Geographic Distribution

The Greenfin darter is primarily restricted to the fast flowing, mountainous streams and rivers of the Upper Tennessee River drainage area, in North Carolina, Georgia, and Tennessee. The species' range stretches from the upper Holston and Watauga rivers, south through the French Broad and Little Tennessee rivers, and ultimately ends at the Hiwassee River. The inherent difficulty in surveying small, fast flowing streams make assessing the actual abundance and range of this species particularly challenging. Additionally, despite it's abundance, E. Chlorobranchium populations are geographically patchy due to the species preference for a specific microhabitat. Nevertheless, the Greenfin does not appear to be threatened throughout its range.

Ecology

Etheostoma Chlorobranchium are benthic insectivores, feeding mainly on insect larvae in cold, high-elevation creeks and rivers. A study by Bryant et al. revealed that the diet of the Greenfin darter may be the most diverse in the genus, with some individuals' guts containing up to 15 different species of insect. Predators of E. chlorobranchium are mainly larger freshwater fish such as smallmouth bass (Micropterus dolomieu) and madtoms (Genus Notorus). The species is relatively abundant, and has been found to hybridize with E. camurum and E. Rufilineatum, where ranges overlap. Like many other darter species, the Greenfin has adapted morphologically to reduce drag and allow stationary positioning on the substrate even in the midst of fast flowing riffles. Because of this, any environmental disturbance that reduces the availability of this microhabitat will have a disastrous effect on Greenfin populations.

Life History

E. Chlorobranchium spawning occurs from late May through to early August. Females bury themselves in the substrate in areas protected from strong currents, and release eggs upon the arrival of a mate. The male may remain at the spawning site for several hours, guarding the eggs. Growth is extremely rapid, with juveniles reaching 45mm in just a year. Mean length is 62mm, with some individuals reaching as much as 110mm. Lifespan can be up to 5 years. E. Chlorobranchium is thought to be the largest species in the sub-genus Nothonotus. There are no studies suggesting recent life history changes, whether anthropogenic or otherwise.

Current Management

E. Chlorobranchium is not currently managed in any of the states it occurs in, and has not been evaluated by the IUCN , although it is classified as state threatened in Georgia. However, the species is found and protected in the Great Smokey Mountains National Park and the Southern Appalachian Biosphere reserve. Greenfin populations are certainly vulnerable to siltation, water impoundment (or any change to water velocity), and agricultural runoff. A close relative, E. Camurum, has seen huge population declines due to anthropogenic environmental disturbance, and is listed as critically imperiled in several states . Hybridization between E. Chlorobranchium, E. Camurum, and E. Rufilineatum does not appear to be a threat to the species. Additionally, climate change may force the Greenfin into higher and higher elevations, and into smaller streams. This will almost certainly lead to population declines. Because of its position as an important food source for larger fish in the Tennessee River Drainage area, it is important that this species is both assessed and monitored in the future.

Management Recommendations

Very little is known about actual population sizes of E. Chlorobranchium. Because they are found primarily in swift flowing, boulder filled streams, sampling with seines is difficult. Electroshock techniques are equally ineffective; the Greenfin, like all darters, lacks a swim bladder, and sinks to the substrate when not swimming (Fishes of TN). Nevertheless it is imperative that efforts are made to monitor the health of E. Chlorobranchium populations. Projects should focus on streams and rivers affected by agricultural runoff or human mediated water velocity change. Sampling should take place several times a year for several years, as there are no historic records to compare modern populations to. If the Greenfin is truly in stasis, unaffected by human development, surveys could be relaxed to once every year or two.