|Scientific Name:||Crystallaria asprella|
|Species Authority:||(Jordan, 1878)|
|Red List Category & Criteria:||Vulnerable A2c ver 3.1|
|Reviewer/s:||Smith, K. & Darwall, W.R.T.|
|Facilitator/s:||Hammerson, G.A. & Ormes, M.|
This species is listed as Vulnerable because its population size may have declined by more than 30 percent over the past 10 years, based on declines in habitat extent and quality. If the decline has been less than 30 percent, listing as Near Threatened may be appropriate, unless population size is fewer than 10,000. Population size is unknown but may be fewer than 10,000. If population size is fewer than 10,000, listing criteria would include C1. Area of occupancy is unknown but may be less than 2000 sq km. The species occurs in more than 10 locations. Distribution is probably not severely fragmented.
|Range Description:||The historical range included the Mississippi River basin, from Wisconsin (Becker 1983) and southwestern Minnesota and the Wabash River, Indiana, south to southeastern Oklahoma (Miller and Robison 2004), northern Louisiana, southern Mississippi (Ross 2001), Gulf Slope in the Escambia, Mobile Basin, Pascagoula, and Pearl River drainages, Florida, Alabama, and Mississippi (Ross 2001, Boschung and Mayden 2004, Page and Burr 2011). The species is now absent from much of the former range, including almost all of the northeastern portion of the range in Indiana and Illinois (Smith 1979), and it has apparently disappeared from much of the upper Mississippi River basin. It is rare in Wisconsin (Becker 1983), Minnesota, Iowa, and Missouri (Pflieger 1997).|
|Range Map:||Click here to open the map viewer and explore range.|
This species is represented by fewer than 100 occurrences (subpopulations).
Total adult population size is unknown but presumably is at least several thousand. This species is not easily detected using standard fish survey methods.
The Crystal Darter is common in only a few streams; it is localized and generally rare (Page and Burr 2011). In Missouri, the species never has been common in collections, with most records represented by three or fewer specimens (one collection of 11 specimens) (Pflieger 1997). Crystal Darters appear to be rare in the Elk River, West Virginia; Osier (2005) captured only two specimens during 20 sampling occasions during 2002-2004.
This species has undergone a substantial long-term decline in extent of occurrence, area of occupancy, number of subpopulations, and population size. It has been extirpated from 5 states in the northeastern portion of the historical range. In Iowa, recent records are available from Turkey Creek and pools 9 and 11 of the Mississippi River (Iowa Aquatic Gap Fish Atlas). In Missouri, the species probably is extirpated in the St. Francis River and Little River drainages, and it may no longer occur in the Meramec River (Pflieger 1997). The Crystal Darter was formerly abundant in the Tombigbee River in Mississippi but has not been collected there since 1981; the species is probably extirpated from the Tombigbee drainage in Mississippi, with the possible exception of the Buttahatcheee River (Ross 2001). The few individuals in the Tombigbee River and its major tributaries in Alabama may "represent viable populations or stragglers destined for extirpation" (Boschung and Mayden 2004). The species was once common in the Alabama River in Wilcox and Monroe counties (Alabama) but has not been collected there since 1975 (Boschung and Mayden 2004). The last collection in the Pascagoula River system was in 1933, although apparently suitable habitat still remains (Boschung and Mayden 2004).
Population size has probably declined over the past 10 years (three generations probably less than 10 years), but the rate of decline is unknown. This species is declining in most areas (Mayden pers. comm. 1994, Burr pers. comm. 1993, Douglas pers. comm. 1993, Shute pers. comm. 1993; Ross 2001). With continued habitat exploitation and degradation, the decline is expected to continue (Mayden pers. comm. 1994). In Alabama, the darter's conservation status has deteriorated since the late 1970s, and the extent of suitable habitat continues to decline (Boschung and Mayden 2004). Lyons (pers. comm. 1994) characterized Wisconsin populations as rare but probably stable. Some populations in the southern portions of the range may be stable (Stewart pers. comm. 1993).
Populations tend to fluctuate. A population may appear abundant in a locality for a time and then be essentially absent (Shute pers. comm. 1994).
|Habitat and Ecology:||This darter inhabits clear to slightly turbid water of raceways and swift to moderately swift riffles of small to medium rivers with expanses of clean sand or gravel; it does not associate with mud, clay, or submerged vegetation (Pflieger 1997, Ross 2001, Boschung and Mayden 2004). Usually it occurs in water more than 60 centimetres deep with strong current. Individuals often bury themselves in sand with only the eyes protruding, or they may hide under rocks. In Arkansas, this species was collected typically at depths of 114-148 centimetres and velocities of 46-90 centimetres per second; predominantly on gravel, small cobble, and patches of sand (George et al. 1996).|
The Crystal Darter is vulnerable to siltation and other forms of pollution from urbanization, strip-mining, logging, natural gas exploration, and improper agricultural practices, as well as stream alteration projects, such as damming, dredging, and channelization.
Dredging for navigation is believed to be a major threat in the upper Mississippi River system. Waterway construction has destroyed and degraded habitat in some areas. Construction of the Tennessee-Tombigbee Waterway, which connected the Tennessee and Tombigbee drainages, was followed by declines in Crystal Darter populations (Ross 2001, Boschung and Mayden 2004). Jay Hatch and Konrad Schmidt captured a specimen at a designated and active dredge spoil disposal site in the Mississippi River. Possibly the unconsolidated material gradually eroding back into the river provided a soft and suitable substrate for the Crystal Darter (Ray Katula, The Native Fish Conservancy).
The Mississippi River probably no longer serves as an effective dispersal corridor due to its increased silt load (Bauer and Clemmer pers. comm. cited by Boschung and Mayden 2004). In the lower Cahaba River, Alabama, the species is threatened by increased siltation and eutrophication perpetuated by upstream urbanization and strip mining (Boschung and Mayden 2004).
Populations remaining in the Mobile Basin are isolated from one another by dams and silty impoundments (Boschung and Mayden 2004).
This fish requires swift moving currents and therefore is susceptible to water flow modifications (dams, etc.). Altered flows due to hydropower dams are a possible problem in the lower Chippewa and St. Croix rivers in Wisconsin (Lyons pers. comm. 1994).
Introduction of nonindigenous fish species is another potential threat. Newly introduced species could compete with or prey on the Crystal Darter (Bauer and Clemmer 1983).
Localized populations are vulnerable to extirpation from single destructive events such as spills of toxins.
Crystal Darters are relatively tolerant of nondestructive intrusion, though heavy recreational use of habitat potentially could be excessively disruptive.
Beneficial management practices include those that limit and/or control activities such as stream channelization, impoundment, removal of riparian vegetation, and careless agricultural practices (Bauer and Clemmer 1983). Range-wide abundance and distribution are in need of further study (Stewart pers. comm. 1993, Burr pers. comm. 1993). Long-term population monitoring is needed to assess trends and guide management. This species is detected most readily by nocturnal sampling.
More information on basic ecology is needed.
Protection from erosion and point-source pollutants should encompass entire watersheds. Broad riparian buffer strips, stiff enforcement of enhanced pesticide regulations, upland erosion control, and modern pollution control systems may be needed to prevent habitat degradation in some areas. Threats from dredging, toxic spills, and regulated flows from hydropower dams need to be addressed.
|Citation:||NatureServe 2013. Crystallaria asprella. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 09 December 2013.|
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