| Gulf darter | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Percidae |
| Genus: | Etheostoma |
| Species: | E. swaini |
| Binomial name | |
| Etheostoma swaini (Jordan, 1884) |
|
The common name of Etheostoma swaini is the Gulf darter. Etheostoma is a diverse genus of small freshwater fish in the family Percidae. It contains nearly 140 member species; most are native to North America. It is one of the 324 fish species found in Tennessee.
Contents |
The purpose of this paper is to portray a feasible monitoring plan for the Gulf darter (Etheostoma swaini). Modern societies are constantly expanding, therefore, increasing the amount of waste and byproducts that accumulate in lakes and rivers. This ultimately results in contamination and can greatly impact fish habitats across the globe, specifically those inhabited by E. swaini. Other members of the Etheostoma genus have become endangered due to such urban landscapes. Therefore it is extremely important to develop a management plan in order to prevent the endangerment and possible extinction of E. swaini. The proposed management plan in this paper will explore our basic understanding of E. swaini's- geographic distribution, ecology (i.e. diet, prey, and predators), life history, and any current management plans that have already been instituted. Examination of the types of climate zones as well as specific types of streams and lakes that E. swaini occupies will allow proper evaluation of any urban threats to the species’ survival. Important ecological aspects such as stream velocity preference as well as life history traits such as reproductive cycles will also be examined to expose possible threats to E. swaini. The basic understanding of such key characteristics is necessary in order to prevent invasive species and habitat destruction. Lastly, any current management plans in place for other members of the Etheostoma genus or similar species should be examined in order to properly assign measures that can accurately protect E. swaini as seen by past successes and failures of conservation attempts. Ultimately, a solid management plan for E. swaini is necessary to prevent endangerment and possibly extinction, as seen by many other darter species. Understanding as many characteristics as possible will ultimately result in a stronger management plan that should last and preserve the species diversity in the Etheostoma genus
E. swaini is known for its laterally compressed, robust body with small conical head, slightly joined gill membranes and a wide frenum on its upper lip. The back has seven to nine diffuse, square saddles and a distinctive light predorsal stripe. Horizontal light and dark banding is evident along the sides. Along their sides breeding males have alternating red-orange and blue-green vertical bars that are most developed near the caudal fin.[1]
E. swaini generally inhabits small- to moderate-size creeks and occurs over a sand or sandy mud bottom, often in association with aquatic vegetation or a layer of organic debris. E. swaini can be found from Lake Pontchartrain, Louisiana east to the Ochlockonee River drainage, Florida and in many eastern tributaries to the Mississippi River from Buffalo Bayou, Mississippi north to the Obion River system of Tennessee and Kentucky. E. swaini is frequently encountered in extremely shallow locations, often foraging in water less than 5 cm deep.[2]
In most creeks the microhabitat of E. swaini is characterized by moderate to heavy amounts of aquatic vegetation, primarily Sparganium americanum. E. swaini actively forage in and among clumps of vegetation and they also utilize the areas of reduced current downstream from these clumps as resting sites. In larger, predominately vegetated creeks, E. swaini inhabits quiet streamside areas of sand and sand-silt substrates. In the smallest creeks, however, E. swaini may occasionally be found in shallow, swift riffles formed by logs, rocks or vegetation.[2]
In its preferred microhabitat, E. swaini is usually associated with Noturus leptacanthus and Percina nigrofasciata, and often with Ichthyomyzon gagei larvae. P. nigrofasciata appears to be the most ecologically similar species to E. swaini; however, the extent to which they may compete is not known.[3] P. nigrofasciata forage in a much wider variety of microhabitats and did not exploit vegetation or organic debris to the extent E. swaini does.
E. swaini are classified as insectivores, feeding on small invertebrates; for example, blackflies, mayflies and dragonflies. One studied examined the diet of E. swaini and found that larval dipterans are the most important food items in fish of all sizes, in which Chironomids were found in 71-100% of the stomachs that were examined. Following the food web, it makes sense that the primary predators of E. swaini are larger freshwater fish such as Lota lota (burbots), Notorus flavus (stonecats), and Micropterus dolomieu (smallmouth bass). E. swaini, like many other darter, species have the ability to maintain position on the substrate in flowing water.[4] This unique characteristic plays a key role in its microhabitat preference.
In regards to microhabitat, E. swaini has been shown to prefer creeks and rivers that have a rocky substrate and swift moving riffles. This microhabitat preference has been suggested to be due to oxygen levels in the water during seasonal changes or simply due to other factors such as feeding or shelter related habitat preferences. Because E. swaini has such a low tolerance for brackish water, human-induced changes such as pollution or sewer drainage could cause a huge negative impact on E. swaini abundance.[5]
Darters have a wide range of life histories; however it has been seen that size correlates with most life history characteristics. For example, larger darters grow faster, live longer, produce bigger clutches, and have longer reproductive spans.[6] Furthermore, it is assumed that mate selection by female darters is common. A summary of the life history characteristics of E. swaini, are: average size 5.3 cm, maximum growth 7.8 cm, maximum age 35 months, and average clutch size 39. E. swaini mates during mid-February to late March, typically when water temperature is between 5.5-17.0°C and congregate on gravel shoals where the stream leaves a pool to mate. Once mates are selected, the fish mate repeatedly for several days until the female lays about 90 eggs.[6] Once the eggs are laid, female E. swaini will begin burrowing into the gravel submerging herself, and the eggs, as a form of protection. Males tend to exhibit territorial behavior during breeding season.
Currently, the largest threat to E. swaini is run-off and pollution due to urbanization. For instance, one study found that the development of an interstate negatively affected the abundance of several fish species, including E. swaini, because of decreasing quality of water of the nearby creek.[7] Therefore, it is extremely important that we monitor run-off and pollution that drains into our rivers and streams due to the adverse effects that it could have on our fish communities. Currently, management plans consist of reducing nutrient, pesticide, and sediment loadings within such streams.[8] Furthermore, this same study suggests that conservation practices should be a combination of both physical habitat monitoring and water chemistry monitoring because it would benefit fish communities within head-water streams more than just implementing one conservation practice or the other.[8] Although there are broad management plans in place for many rivers and streams and their fish communities as a whole, there are not currently any management plans in place specifically designed for E. swaini. The lack of protection is probably because E. swaini is one of the most abundant darter species. Although the E. swaini may be abundant now, many other darter species have become endangered or extinct and therefore, we should implement a better management plan for E. swaini.
E. swaini does not currently have any management plans in place designed specifically for it. However, due to its sensitivity to water purity and to the fact that it is a primary food source for many larger freshwater fish, it would suffice to say that a better management plan is in need in order to help maintain healthy freshwater ecosystems that it occupies. In order to monitor and manage E. swaini, it would be ideal to have a good estimate of the species abundance. To do so, one would need to use seines to catch E. swaini and count the numbers of species present in known streams and rivers that it occupies and repeat this process several times a year; doing so would provide a good estimate for average E. swaini species abundance. Once an estimate for E. swaini abundance is determined, monitoring the annual number of species would show influxes in the abundance of E. swaini or a decline in the abundance of E. swaini compared to its average abundance. Management plans should include monitoring watershed from nearby urban areas (i.e. monitoring chemical run-off from agriculture or plants) and monitoring overfishing (since E. swaini are a primary source of prey for many larger freshwater fish, it is important to keep the balance). Invasive species could also potentially pose a threat to the E. swaini, and if they were to upset the balance of the freshwater ecosystem, measures would need to be made in order to remove such species. Along with pollution from humans, the main biological factor that is deterring the population growth of this fish can be contributed to siltation, which reduces the amount of oxygen available for them to breathe and can also lead to the smothering of their eggs they bury after they breed. Future management plans should include finding more locations of E. swaini and decreasing further habitat destruction in known distributions by stating it as a fish of concern by state law
Ruple D. L., McMichael Jr. R. H., Baker J. A. 1984. Life History of the Gulf Darter. Environmental Biology of Fishes 11:121-130.
Warren Jr. M. L., Burr B. M., Walsh S. J., Bart Jr. H. L., Cashner R. C., Etnier D. A., Freeman B. J., Kuhajda B. R., Mayden R. L., Robison H. W., Ross S. T., Starnes W. C. 2000. Diverstiy, Distribution, and Conservation Status of the Native Freshwater Fishes of the Southern United States. Fisheries 25:10, 7-31.
Paine M. D. 1990. Life history tactics of darters (Percidae: Etheostomatiini) and their relationship with body size, reproductive behavior, latitude and rarity. Journal of Fish Biology 37: 473-488.
Ritzi, C.M., B. L. Everson, J. B. Foster, J. J. Sheets, and D. W. Sparks. 2004. Urban ichthyology: changes in the fish community along an urban-rural creek in Indiana. Proceedings of the Indiana Academy of Science 113: 42-52.
Smiley, P.C., R. B. Gillespie, K. W. King, and C. Huang. 2009. Management implications of the relationships between water chemistry and fishes within channelized headwater streams in the Midwestern United States. Ecohydrology 2: 294-302.
Carlson, R.L and G.V. Lauder. 2010. Living on the Bottom: Kinematics of Benthic Station-Holding in Darter Fishes (Percidae: Etheostomatinae). Journal of Morphology (271): 25-35.
Froese, R. and D. Pauly. 2011. FishBase. Etheostoma swaini. World Wide Web electronic publication. www.fishbase.org, version http://www.fishbase.org/summary/speciessummary.php?id=3472.
Fishes of Alabama and the Mobile Basin. 2011. Gulf Darter. Alabama Department Conservation and Natural resources. http://www.outdooralabama.com/fishing/freshwater/fish/other/darters/gulf/.