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Micropterus cataractae Williams and Burgess, 1999
Shoal Bass
Federal Protection: No US federal protection
State Protection: No Georgia state protection
Global Rank: G3
State Rank: S2
Element Locations Tracked in Biotics: Yes
SWAP High Priority Species (SGCN): Yes
Element Occurrences (EOs) in Georgia: 78
Habitat Summary for element in Georgia: Large river, shoal and fluvial specialist
Shoal bass are an average sized black bass that can reach a length of 640 mm (25 inches) and a weight of 3 kg (6.6 lbs) or more. In adults, the background coloration of the dorsal and lateral areas of the head and body ranges from dark olive green to almost black. A dusky to black blotch is present on the posterior portion of the opercle and three dark radiating lines are found on the cheek. The body has 10-15 midlateral and 6-8 supralateral dark, vertically elongate blotches, often resembling tiger stripes. A large quadrate to rectangular blotch is present at the base of the tail. Maxilla extends posteriorly beyond the eye. A tooth patch is usually absent on the tongue. Juveniles < 100 mm often have a dusky tan to greenish background coloration with long distinct lateral bars ending in a wedge-shaped spot at the base of the tail. Unlike many black bass species, shoal bass do not exhibit sexual dimorphic growth patterns, although females typically live longer than males (Sammons et al. 2019).
Two native species of black bass are sympatric with shoal bass: largemouth bass Micropterus salmoides and Chattahoochee bass M. chattahoochae. Three more have been introduced: smallmouth bass M. dolomieu, spotted bass M. punctulatus, and Alabama bass M. henshalli. Largemouth bass are the most easily distinguished from the others, as there is almost complete separation between the spinous and soft dorsal fins, no tooth patch on the tongue, a maxilla that extends well beyond the eye (in adults), and a midlateral row of continuous dark blotches, often resembling a stripe, is usually present. Further, no ventrolateral rows of spots are found on the body of largemouth bass. Smallmouth bass generally have a brownish-green body coloration, are typically marked with vertical bars that are longer and thinner than shoal bass and have a relatively small head and mouth (maxilla does not extend past the eye in adults). They also lack ventrolateral spots, a basicaudal blotch, and typically do not have a tooth patch. Chattahoochee bass is the smallest described black bass species in Georgia, rarely exceeding 205 mm (10 inches). It has a round to oval patch of teeth on the tongue and the dorsal, anal, and caudal fins all have varying amounts of reddish-orange coloration, especially near the spawning period. Alabama bass and spotted bass have a tooth patch on the tongue, a midlateral series of dark blotches that often form a lateral band, noticeable ventrolateral rows of dark spots, and no coloration on the fins. Alabama bass and spotted bass closely resemble each other but can be reliably distinguished by use of lateral line scales, circumpeduncle scale counts, and at times by differences in the lateral blotching pattern (Baker et al. 2008). Frequent hybridization between native and non-native species often complicates identification without genetic data (Sammons et al. 2015).
Shoal bass are habitat specialists, occupying areas with rocky substrate and moderate to fast current (Wheeler and Allen 2003; Goclowski et al. 2013). The species typically inhabits medium to large-sized rivers both above and below the Fall Line and is not commonly found in smaller streams (Williams and Burgess 1999). Shoal bass are intolerant of reservoir habitats and generally will not voluntarily move into them (Sammons and Earley 2015), although studies have shown that they will move out of them to re-enter lotic habitats when relocated by anglers during tournaments (Ingram et al. 2013). Although shoal bass commonly use rocky habitats when available (Wheeler and Allen 2003; Goclowski et al. 2013), they are readily found using woody debris as cover in coastal plain habitats (Sammons and Goclowski 2012). Regardless of season, shoal bass are generally found in areas characterized by current and are rarely found in backwaters or other off-current areas (Goclowski 2010). Shoal bass typically spawn in large shoal complexes, and often undergo long migrations to reach these areas (Sammons 2015). Juveniles appear to remain in spawning habitats until at least mid summer, and slowly disperse throughout the river sometime thereafter (Goclowski 2010). In streams, most fish may spawn in the largest shoal complex available, usually located somewhere near the Fall Line (Cottrell 2018).
Shoal bass diets are varied, consisting primarily of crayfishes, fishes, and insects. Generally, diets of small fish (< 200 mm TL) are dominated by insects, but insects decline in diet importance as fish grow larger (Wheeler and Allen 2003; Sammons 2012). Primary insects consumed by shoal bass include mayflies, odonates, and hellgrammites, and diets consisting of 200-300 individual mayfly naiads have been observed in both the Chipola and Flint rivers (Wheeler and Allen 2003; Sammons 2012). Diets of larger fish are composed mostly of crayfishes and fishes. Shoal bass in the Chipola River and the Flint River both exhibited an ontogenetic diet shift, with crayfish becoming increasingly more dominant in the diet as fish grew (Wheeler and Allen 2003; Sammons 2012). However, shoal bass in the Flint River were also more likely to be piscivorous at larger sizes; thus, fishes were also an important diet component of larger fish in that system (Sammons 2012). Primary fishes identified in shoal bass diets include various minnows, darters, and madtoms (Wheeler and Allen 2003; Sammons 2012).
Shoal bass nests have been observed being constructed as shallow depressions in coarse gravel or sand (Hurst et al. 1975; Boshung and Mayden 2004); however, shoal bass nests are often not readily identifiable (Bitz et al. 2015; Cottrell 2018). Chipola River shoal bass constructed nests in areas predominately composed of boulder and rocky habitat (Bitz et al. 2015). Shoal bass appear to spawn in relatively small areas behind current refuges such as large boulders, clumps of vegetation, or in lower ends of small pools (Boshung and Mayden 2004; Johnston and Kennon 2007; Bitz et al. 2015). Across their range, shoal bass usually begin spawning in early April and spawning activity continues until mid or late June. Hatch dates of age-0 fish collected during summer in the Flint River ranged from late March until mid-May across three years, and hatching durations of these cohorts was typically about one month long (Sammons and Goclowski 2012). Hatching occurred at water temperatures ranging from 15 to 22 °C, which matches approximate ranges of spawning water temperatures reported by other authors (Hurst et al. 1975; Boshung and Mayden 2004; Bitz et al. 2015). Successful hatching of shoal bass in the Flint River, Georgia, generally occurred after water levels stabilized following large spates of water moving through the system; however, recruitment was not affected by floods or droughts occurring during their first growing season (Sammons and Goclowski 2012; Sammons et al. 2019). Shoal bass attain sexual maturity by age 3 and typically live 10-12 years and ocassionally longer. Natural mortality is likely similar to other southeastern bass species, which is approximately 20-25% annually. Fecundity of individual fish ranges from 900 to 35,000 eggs (Kern et al. 2020), which is within the range reported for other Micropterus species.
Since the species description (Williams and Burgess 1999), many studies have been conducted on populations in the Flint River basin (e.g., Sammons 2012; Goclowski et al. 2013, Ingram et al. 2013; Sammons 2015; Ingram et al. 2019; Kern et al. 2020). In contrast, fewer studies have been conducted on shoal bass biology and ecology in the Chattahoochee River Basin (e.g., Katechis 2015; Sammons and Earley 2015; Cottrell 2018; Taylor et al. 2018). Given the large threat of genetic introgression with native congeners, there is a critical need for frequent monitoring of these populations for abundance and genetic integrity. Research has demonstrated that these impacts can happen rapidly (< 10 years; Taylor et al. 2018). The Flint River is the only portion of the shoal bass range in Georgia that is sampled on a regular basis by GADNR biologists. No work has occurred on the various tributaries of the Flint River, and the status of shoal bass in those systems is unknown. Some survey work has also been conducted in the lower-most portion of the Chattahoochee River above Lake Lanier. Also, the Chattahoochee River between West Point Dam to Columbus has been sampled haphazardly over the last 10-15 years, usually for brood stock collection rather than actual abundance monitoring. Virtually no work has occurred in tributary streams other than a M.S. thesis by Auburn University (Katechis 2015).
A factor that complicates historical and current distributional records of shoal bass across its range is the fact that the species is large, mobile, and tends to be found in deeper areas with high flows, making it difficult to capture using conventional stream sampling gears such as seine or backpack electrofishers. Thus, general species surveys are often unsuccessful at capturing any individuals and are certainly insufficient to assess population status of the species. Many areas where shoal bass are found are inaccessible to boat electrofishing units and are too large for backpack units, requiring the use of novel sampling gears such as the canoe electrofishing unit used by Katechis (2015), or raft electrofishing units (Hughes et al. 2002).
Given that tributary populations are smaller and likely more vulnerable than main-river populations, comprehensive surveys of larger tributaries of the Flint River should be prioritized to more clearly direct restoration efforts. Also, fish community surveys of these tributaries will allow assessment of species associations with shoal bass and identify common threats that could be addressed through implementation of watershed management plans. More knowledge of the status of shoal bass and associated species in major tributary streams of the Flint and Chipola rivers will help direct restoration and protection efforts more effectively and may be able to garner funding for these activities from a wider variety of sources.
Shoal bass are endemic to the Apalachicola-Chattahoochee-Flint River (ACF) Basin in Alabama, Georgia, and Florida. In the Chattahoochee River, shoal bass occur naturally in the unregulated portion of the river above Lake Lanier and are supported by supplemental stocking in the main channel of the river below Morgan Falls Dam in downtown Atlanta, Georgia. The species has apparently been extirpated from the main river channel from Atlanta downstream to West Point Lake; however, several populations have been found in major tributary streams or below dams in the Chattahoochee River from West Point Dam to Columbus, Georgia (Sammons and Maceina 2009; Katechis 2015). Shoal bass are not currently known from the Chattahoochee River or tributary streams south of Columbus, Georgia. Shoal bass occur naturally throughout the entire Flint River and some major tributaries, except in the areas impounded by Lake Blackshear, Lake Worth, and Lake Seminole (Williams and Burgess 1999). Populations from Crisp County Dam downstream to Lake Seminole have been supported by supplemental stocking by GADNR since the late 1970s due to concerns about hydropeaking flows on recruitment. Additionally, the species was stocked outside its native range into the Ocmulgee River in east-central Georgia, a tributary of the Altamaha River, in the mid 1970s (Williams and Burgess 1999). Shoal Bass are well established in the main channel and major tributaries of the Ocmulgee River from Llyod Shoals Dam to at least 160 km downstream and continue to expand towards the confluence with the Oconee River. The species has been extirpated in Alabama and exists only in the Chipola River in Florida (Williams and Burgess 1999; Woodside et al. 2015). Thus, Georgia likely contains about 90% of shoal bass currently occupied range in the world.
Threats to shoal bass include increased urbanization, land-use changes, dams, and introduction of non-native congeneric species. A significant portion of the area encompassed by the range of shoal bass has undergone rapid urbanization and associated land-use changes which have been linked to lower species diversity and water flows in streams and rivers (Walters et al. 2003; Helms et al. 2005; Johnston and Maceina 2009). These threats are likely to increase in the future, as the human population of the southeastern U.S. continues to expand. The mainstem Chattahoochee River in Georgia has been impounded by a series of dams that have reduced the amount of riverine habitat to appromimately one-half of natural conditions (A. Lawrence, U.S. Fish and Wildlife Service, personal communication). The likely overall effect of dams in the Chattahoochee River has been to reduce a continuous population of shoal bass into a series of isolated populations of limited genetic diversity and low effective population size (Sammons and Maceina 2009; Dakin et al. 2015). In contrast, the Flint River is mostly undammed and the shoal bass population there remains mostly intact.
There have been a series of illegal introductions of non-native Micropterus species into lotic systems in Georgia that formerly contained only native black bass. Williams and Burgess (1999) provide a detailed summary of introductions of spotted bass and Alabama bass into the lower Flint River and throughout the Chattahoochee River system. Additionally, spotted bass were found above Lake Blackshear on the Flint River in 2005, and their population has grown substantially since (Sammons and Goclocwski 2012). Within 10 years following their introduction, smallmouth bass impacted the genetic integrity of Shoal Bass populations in the Chattahoochee River near Atlanta (Dakin et al. 2015; Taylor et al. 2018). Introgression between shoal bass and both native and introduced Micropterus spp. has been documented across the range of the species (Alvarez et al. 2015; Dakin et al 2015; Tringali et al. 2015). The long-term genetic consequences of these unauthorized introductions on shoal bass remain unknown but are likely the greatest immediate threat facing conservation of this species.
Shoal bass has been assigned a status of Special Concern by the American Fisheries Society Endangered Species Committee (Jelks et al. 2008), classified as a species of High Conservation Concern in Alabama, and listed as a species of greatest conservation need by the Florida Fish and Wildlife Conservation Commission. The Shoal Bass is recognized as a high priority species in Georgia's State Wildlife Action Plan (Georgia DNR 2015) and was designated as the State'e official riverine sport fish by the Georgia legislature in 2020. Although the species may be considered stable overall, extensive hybridization with non-native congeners and fragmentation by numerous dams have resulted in severe declines, especially wihtin the Chattahoochae River system.
A rangewide management plan was developed for shoal bass in 2017 by the Southeastern Aquatic Resources Partnership under the Native Black Bass Initiative. A team of shoal bass biologists identified primary threats and conservation actions for specific populations. Hybridization with non-native congeners was identified as the top threat to shoal bass throughout the Flint and Chattahoochee river systems in Georgia. Barriers to movement was identified as a major threat in the Fall Line area of the Chattahoochee. Sedimentation was considered a secondary threat to shoal bass throughout most of their range, with poor water quality and low summer flows being the second-most identified threat in the Chattahoochee River between Atlanta and West Point Lake and the Flint River below Lake Blackshear, respectively.
Based on current knowledge of distribution of stable shoal bass populations, 9 sub-basins were identified for conservation efforts in Georgia.
1) Mainstem Chattahoochee River above Lake Lanier
2) Chestatee River
3) Sweetwater Creek
4) Flat Shoals Creek
5) Mulberry Creek
6) Mainstem Flint River above Lake Blackshear
7) Mainstem Flint River between Lake Blackshear and Lake Chehaw
8) Mainstem Flint River between Albany Dam and Lake Seminole
9) Ichawaynochaway Creek
All of these populations currently can or do support quality fisheries for shoal bass and comprise the majority of opportunities for anglers seeking the species. Efforts should be made to maintain or increase quality of these fisheries, including angler access, fishing regulations, and stocking as needed. Monitoring programs for species abundance, composition, shoal bass size structure, and genetic integrity should be implemented or continued where already ongoing. Land acquisition for both access and watershed protection will be vital components for successful shoal bass management and conservation in these areas.
Populations of shoal bass with documented declines over the last 20-30 years were considered high-priority candidates for restoration efforts. Mechanisms behind the decline of shoal bass in these systems are largely unknown, but likely include urbanization, poor agricultural practices, and hybridization/competition with non-native congeners. The following is a list of shoal bass populations that are prioritized for restoration efforts.
1) Soque River
2) Big Creek
3) Dog River
4) Whooping Creek
5) Hillabahatchee Creek
6) Mainstem Chattahoochee River between West Point Dam and Bartletts Ferry Reservoir
7) Mountain Oak Creek
8) Mainstem Chattahoochee River between Oliver Dam and Walter F. George Reservoir
Some of these populations still support small populations, but abundance of shoal bass has appeared to decline over the last 10-15 years, despite little recognizable change in habitat or water quality. Others once supported small fisheries with limited access, but the population has declined to almost undetectable levels and non-native congeners now comprise the majority of black bass collected in these systems. Regardless of any habitat and watershed restoration efforts undertaken in these sub-basins, reduction of non-native congeners followed by restocking of pure shoal bass will have to be included for restoration of the species to be successful.
An additional management action includes surveys in tributaries in the Flint River system where potentially viable but undocumented populations of shoal bass may exist.
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Cottrell, A. M. 2018. Movement and habitat use of shoal bass Micropterus cataractae in two Chattahoochee River tributaries. M.S. thesis. Auburn University, Auburn, Alabama.
Dakin, E. E., B. A. Porter, B. J. Freeman, and J. M. Long. 2015. Hybridization threatens shoal bass populations in the upper Chattahoochee River basin. Pages 491-502 in M. D. Tringali, J. M. Long, T. W. Birdsong, and M. S. Allen, editors. Black bass diversity: multidisciplinary science for conservation. American Fisheries Society, Symposium 82, Bethesda, Maryland.
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Sammons, S.M., and M.J. Maceina. 2009. Conservation status of shoal bass in Alabama: distribution, abundance, stocking efficacy, and possible effects of sympatric congeneric black bass in selected tributaries of the Chattahoochee River, Alabama. Final Report submitted to Alabama Division of Wildlife and Freshwater Fisheries, Montgomery.
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Steve M. Sammons
