|Scientific Name:||Percina aurora|
|Species Authority:||Suttkus & Thompson, 1994|
|Taxonomic Notes:||Formerly included in Percina copelandi (see Suttkus et al. 1994).|
|Red List Category & Criteria:||Endangered B1ab(iii)+2ab(iii) ver 3.1|
|Reviewer(s):||Smith, K. & Darwall, W.R.T.|
|Facilitator/Compiler(s):||Hammerson, G.A. & Ormes, M.|
This species is listed as Endangered because its extent of occurrence is less than 5,000 sq km, area of occupancy is less than 500 sq km, number of locations is not more than five, and habitat quality is subject to ongoing declines.
|Range Description:||Historical distribution included localized sites in the Pearl and Pascagoula river drainages, Mississippi and Louisiana (Suttkus et al. 1994); the species is now apparently extirpated in the Pearl River drainage in both Mississippi and Louisiana (Ross 2001, H. Bart and B. Thompson pers. comm. cited by Douglas and Jordan 2002).
Fish collections from the Pearl River drainage (Suttkus et al. 1994) suggest that the darter once inhabited the large tributaries and main channel habitats from St. Tammany Parish, Louisiana, to Simpson County, Mississippi, including sections of the Pearl River, Strong River, and Bogue Chitto River. Bruce Thompson made 27 samples at eight localities on the Bogue Chitto and Pearl rivers (historical locations and others) on 10 different dates from November 1998 to September 1999 and did not find Percina aurora. He did find everything else he would have expected at those sites in those habitats (Steve Shively, Zoologist, Louisiana Natural Heritage Program, pers. comm. 1999).
Museum collections suggest that the Pearl Darter inhabited the main channels of large Pascagoula drainage tributaries from Jackson to Lauderdale counties, Mississippi, including the Pascagoula River, Black Creek, Leaf River, Okatoma Creek, Chickasawhay River, Bouie River, and Chunky Creek. Since 1983, Pearl Darters have only been found in scattered sites in the Pascagoula, Chickasawhay, Chunky, Leaf, and Bouie rivers, and Okatoma and Black creeks (compiled from Bart and Piller 1997 and Ross in press). Bart and Piller (1997) made 27 ancillary collections in 1996 and 1997 from the Pascagoula drainage and collected only 10 Pearl Darters at four sites (the Leaf River at Eastabuchie; lower Leaf River at Merrill; Bouie River downstream of I-59 crossing; and Okatoma Creek at Collins). Three specimens were collected in the Leaf River at Eastabuchie in the spring of 1998, whereas in December 1998 no Pearl Darters were found in the upper reaches of the Leaf River between Eastabuchie and north Hattiesburg (Bart and Ross pers. comm. 1998). No Pearl Darters were found in selected sites of the Chunky River in 1995 and 1997 (Bart pers. comm. 1999). Suttkus et al. (1994) speculated that portions of the Leaf River and possibly the lower Black Creek may continue to support reproducing populations even though no recent collecting attempts had been made.
|Range Map:||Click here to open the map viewer and explore range.|
A map in Ross (2001) suggests that the species currently exists in four areas, some of which are represented by at least two known sites.
Even before its description in 1994, the Pearl Darter was considered rare and of conservation concern (Deacon et al. 1997) because it was uncommon, infrequently collected, and occurred in low numbers (Bart and Piller 1997). The Pearl Darter was collected from only 14% of 716 fish collections from site specific locations within the Pearl River drainage despite annual collection efforts by Suttkus from 1958 to 1973 (Bart and Suttkus 1996, Suttkus et al. 1994). No Pearl Darters have been collected in the Pearl River drainage since 1973, even though Suttkus has made 64 fish collections over the last 25 years from the Pearl River (Bart and Piller 1997). Collection data from Bart and Piller (1997), Bart and Suttkus (1996), Suttkus et al. (1994), and Ross (in press) suggest that the Pearl Darter is very rare in the Pascagoula River system. Bart and Piller (1997) examined Suttkus' work before 1974 and found that only 19 Pearl Darters were collected out of 19,300 total fish in 10 Tulane University Museum of Natural History collections. Additionally, from the "Mississippi Freshwater Fishes Database," Dr. Stephen Ross (in Bart and Piller 1997) estimated the rarity of the Pearl Darter within the Pascagoula drainage from 379 collections (81,514 fish specimens) since 1973, and found only one Pearl Darter collected for every 4,795 specimens.
This fish disappeared from several areas in the Pearl River in the 1970s (Suttkus et al. 1994); now it is regarded as extirpated in that drainage (USFWS 2011). Collections since the early 1980s indicate that the range has decreased by approximately 55 percent (USFWS 2011).
Trend over the past 10 years or three generations is uncertain, but habitat quality and possibly distribution and abundance probably are slowly declining.
|Habitat and Ecology:||Pearl Darters have been collected in slow to moderate currents in deep runs over gravel or bedrock; in sand pools below shallow riffles; in swift (90 cm/second), shallow water over firm gravel and cobble in mid-river channels; and in swift water near brush piles (Bart and Piller 1997, Ross 2001). A single post-spawning individual was collected in a deep sluggish run over silty sand (Bart and Piller 1997). Five breeding males were collected from the Leaf River (Pascagoula system, Mississippi) in shallow water (15 cm) over firm gravel and cobble in mid-channel (Bart and Piller 1997). Suttkus et al. (1994) mentioned that specimens were collected in rivers in slow to swift current over gravel substrate at depths of 0.5 m or more.|
|Use and Trade:||This species is not utilized.|
Summary (USFWS 2011)
"The Pearl Darter is vulnerable to non-point source pollution caused by urbanization and other land use activities; gravel mining and resultant changes in river geomorphology, especially head cutting; and the possibility of water quantity decline from the proposed Department of Energy Strategic Petroleum Reserve project and a proposed dam on the Bouie River. Additional threats are posed by the apparent lack of adequate state and federal water quality regulations due to the continuing degradation of water quality within the species' habitat. The Pearl Darter's localized distribution and apparent low population numbers may indicate a species with lower genetic diversity and would also make this species more vulnerable to catastrophic events." Threat magnitude is regarded as moderate to low (USFWS 2011).
Removal of riparian vegetation and extensive cultivation adjacent to rivers have caused excessive rapid runoff, bank erosion, channel scouring, and silt deposition in the Pearl River drainage, evidently resulting in large population declines and possible extirpation (Suttkus et al. 1994).
Because of its restriction to the Pascagoula drainage and localization to specific habitats, the Pearl Darter is vulnerable to nonpoint source pollution, changes in river and stream geomorphology, and other human-induced threats to its environment, such as dam construction. Nonpoint source pollution from land surface runoff can originate from virtually all land use activities, and may include sediments, fertilizers, pesticides, animal wastes, septic tank and grey water leakage, oils, and greases. Construction activities that involve significant earthworks typically increase sediment loads into nearby streams. Siltation sources include timber clear cutting, clearing of riparian vegetation, and mining and agricultural practices that allow exposed earth to enter streams. Practices that affect sediment and water discharges into a stream system change the erosion or sedimentation pattern, which can lead to the destruction of riparian vegetation, bank collapse, and increased water turbidity and temperature. Excessive sediments are believed to impact the habitat of darters and associated fish species by making it unsuitable for feeding and reproduction. Sediment has been shown to abrade and or suffocate periphyton, disrupt aquatic insect natural processes, and, ultimately, negatively impact fish growth, survival, and reproduction (Waters 1995).
In the Pascagoula drainage, water quality problems exist on the Leaf River from municipal runoff at Hattiesburg and dioxin contamination at New Augusta and on the Chickasawhay River from brine water releases from oil fields (U.S. Fish and Wildlife Service 1990). Permitted effluents to the Pascagoula River Basin include ammonia, chloride, sodium sulphate, toluene, cyclohexane, and acetone (EPA 1989). Bart and Piller (1997) noted extensive algal growth during warmer months in the Leaf and Bouie rivers, suggesting nutrient and organic enrichment. Municipal and industrial discharges into the watershed, particularly during low water, concentrate pollutants. Releases from the Leaf River Paper Mill at New Augusta affect temperature, dissolved oxygen, and pH in the lower reaches of the Leaf River. Existing housing and urbanization along the banks of the Leaf River between I-59 and Eastabuchie may contribute nutrient loading through sewage and septic water effluent.
The flora and fauna of many coastal plain streams have been adversely affected by accelerated geomorphic processes, specifically headcutting caused by in-stream sand and gravel mining (Patrick et al. 1993). The bed of the Bouie River is considered a significant natural resource by American Sand and Gravel (ASGC) (1995). Historically, ASGC has mined sand and gravel using a hydraulic suction dredge, which is operated within the banks of the Bouie River. Sand and gravel mining also has occurred within and adjacent to the Leaf River. Large sections of the river and its floodplain have been removed over the past 50 years resulting in the creation of very large open water areas that function as deep lake systems (ASGC 1995). Currently, only two permitted mines are operating within the Pascagoula drainage (Stan Phielling, Mississippi Geological Survey, Mining Office, pers. comm. 1998). However, due to the permit exemption category for mining of less than 4 acres and less than 1/4 mile from other mine sites, there are numerous non-permitted operators mining gravel throughout the Pascagoula and Pearl river drainages (Stan Phielling, Mississippi Geological Survey, Mining Office, pers. comm. 1998). Hartfield (1993) and Patrick and Hartfield (1996) investigated the negative impacts of stream erosion due to headcutting on aquatic life in several Mississippi river drainages and believed that the drainages were also experiencing geomorphic instability caused by in-stream sand and gravel mining. Mining in active river channels typically results in incision upstream of the mine (by nickpoint migration) and sediment deposition downstream. The upstream migration of nickpoints or headcutting may cause undermining of structures, lowering of alluvial water tables, channel de-stabilization and widening, and loss of aquatic and riparian habitat. Geomorphic change, particularly headcutting, may cause the extirpation of riparian and lotic (flowing water) species (Patrick et al. 1993). Lyttle (1993) and Brown and Lyttle (1992) found that in-stream gravel mining reduces overall fish species diversity in Ozark streams and favours a large number of a few small fish species. Patrick et al.(1993) documented geomorphic changes that were adversely affecting the Bayou Darter, an endangered species endemic to the Bayou Pierre basin. Bart and Piller (1997) attributed the decline of the Pearl Darter in the Leaf and Bouie Rivers and Black Creek of the Pascagoula drainage to threats from siltation caused by unstable banks and loose and unconsolidated stream beds. Bart (pers. comm. 1999) believes that bank erosion and bar migration on the Leaf River at Eastabuchie is affecting the riffles where the only known spawning of the Pearl Darter is occurring.
The confluence of the Bouie and Leaf rivers, within the Pascagoula drainage, possibly provides significant habitat for the Pearl Darter. Fish collections from this area indicate that it may be a site critical for maintaining the current population of Pearl Darters. The Bouie River at the confluence with the Leaf River is being considered by the city of Hattiesburg to be dammed and used as a major water supply (The Clarion-Ledger, October 28, 1998, Jackson, Mississippi). Such a project would substantially alter and fragment significant occupied habitat of the Pearl Darter in the Bouie River. Locality records (1997) of the Pearl Darter within the gravel mine area of the Bouie River in Hattiesburg place the species within the exact vicinity of the proposed dam (Ross pers. comm. 1998). Pearl Darters have not been collected in impounded waters and are intolerable of lentic (standing water) habitats.
The current range of the Pearl Darter is restricted to localized sites within the Pascagoula River drainages. Genetic diversity has probably declined due to fragmentation and separation of populations. The long-term viability of a species is founded on conservation of numerous local populations throughout its geographic range (Harris 1984). These features are essential for the species to recover and adapt to environmental change (Noss et al. 1994, Harris 1984). Populations of Pearl Darters are becoming increasingly disjunct. This disjunct distribution makes these populations vulnerable to extirpation from catastrophic events, such as toxic spills, large in-stream gravel mining projects, or changes in flow regime.
In general, small species of fish such as the Pearl Darter, which are not utilized for either sport or bait purposes, are unknown to the general public. Therefore, take of these species by the general public has not been a problem. Scientific collecting and take by private and institutional collectors are not presently identified as threats. Scientific collecting is controlled by the State through permits.
Predation upon the Pearl Darter undoubtedly occurs. However, there is no evidence to suggest that disease or natural predators threaten this species. To the extent that disease or predation occur, it becomes a more important consideration as the total population decreases in number.
|Conservation Actions:||More information on the Pearl Darter's ecology, life history, and sensitivity to contaminants, to determine the effectiveness of existing environmental laws and regulations, is needed.|
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|Citation:||NatureServe 2013. Percina aurora. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 19 December 2014.|