Micropterus salmoides

Invasion History

First Non-native North American Tidal Record: 1850
First Non-native West Coast Tidal Record: 1888
First Non-native East/Gulf Coast Tidal Record: 1850

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General Invasion History:

Micropterus salmoides (Largemouth Bass) is native to the Great Lakes, Hudson Bay, and Mississippi basins, from southern Quebec to Minnesota and south to the Florida, the Gulf Coast, and west to New Mexico. It is native to Atlantic drainages from North Carolina south to Florida (Page and Burr 1991). The original range of Largemouth Bass on the southern Atlantic Coastal Plain is uncertain because of probable early introductions. The northern boundary was possibly the James River, but more likely the Tar River drainage, North Carolina (Fuller et al. 1999; Jenkins and Burkhead 1993). Largemouth Bass was widely introduced by United States Fish Commission and state fish commissions. In 1893 the United States Fish Commission shipped mixed batches of 'Black Basses' to 29 states (Worth 1895). Shipments and stocking by United States Fish Commission continued into the 1930s. Stocking has been continued by many state agencies to the present. Largemouth Bass have been introduced to river drainages in 34 states, including Hawaii (USGS Nonindigenous Aquatic Species Program 2018). They have been introduced to Atlantic Coast rivers from Chesapeake Bay to the Kennebec River, Maine, (including the Hudson River via the Erie Canal, Mills et al. 1997), the San Francisco Bay Delta, and the Columbia River (Cohen and Carlton 1999; Fuller et al. 1999; Schmidt et al. 1986). They have also been introduced to Europe, Africa, Mauritius, the Philippines, the West Indies, Hong Kong, and Brazil (Hardy 1978; Lever 1996). Largemouth Bass have been reported from 70 countries worldwide (Food and Agriculture Organization 2018).

North American Invasion History:

Invasion History on the West Coast:

The early history of the 'Black Basses' on the West coast is complicated by confusion between the Largemouth and Smallmouth Basses, which were frequently confused and sometimes introduced in mixed lots. The earliest stocking of Largemouth Bass on the West Coast may have been a release in 1888, in Salem, Oregon, in the Willamette River (Lampman 1946). Another planting of 500 fish was done in 1891, also near Salem (Smith 1895). The first reported catch of this fish in the main stem of the Columbia was 1898, near the site of the present Bonneville Dam. Soon after that, it became a regular market fish in Portland, but in 1913–1915, was classified as game fish (Lampman 1946). Largemouth Bass were common at some waterfront dock sites on the tidal Willamette River in downtown Portland (1987–1989, Farr and Ward 1994), but it was not reported in a survey of Columbia Slough (2008–2009, Van Dyke et al. 2009). Largemouth Bass were found near Astoria, at the mouth of the Columbia by 1936. Many USGS-NAS records of fishing guidebooks indicate that Largemouth Bass are common from Bonneville Dam to the sloughs near Astoria (USGS Nonindigenous Aquatic Species Program 2018).

The earliest documented introduction of the Largemouth Bass to California was probably in 1891, when 600 fish were stocked in the Feather River, and 2,200 in Lake Cuyamaca in San Diego County (Smith 1895). By 1910, 'The rivers, streams, and sloughs throughout the Sacramento and San Joaquin valleys are teeming with them' (California Fisheries Commission 1910, cited by Dill and Cordone 1997). By the 1950s and 60s, Largemouth Bass had spread to many of the freshwater tributaries of San Francisco Bay (Leidy 2007). Typical habitats are warm, slow-flowing waters, creeks and sloughs, with silt-sand substrates, with dense aquatic vegetation (Wang 1986; Moyle 2002). In the tidal freshwaters of the Delta, Largemouth Bass were fairly abundant in 1980s to the 2000s, 4–5th ranking in abundance, 3–13% of the total catch (Feyrer and Healy 2003; Brown and Michniuk 2007; Grimaldo et al. 2012). Since 2004, an increase of Largemouth Bass, Bluegill, and Redear Sunfish has been noted in freshwater Delta waters, associated with an increase in submerge aquatic vegetation (Mahardja et al. 2017). A few specimens were noted in the brackish Suisun Marshes (Matern et al. 2002). Unlike East Coast and Gulf Coast Largemouth Bass, California fish do not appear to utilize brackish waters frequently (Moyle 2002).

In British Columbia, Largemouth Bass have spread to many lakes in the lower Fraser Valley, and are regarded as a threat to fish communities and fisheries in the tidal river (McPhail 2008; Department of Fisheries and Oceans 2011).

Invasion History on the East Coast:

Largemouth Bass are native to the southeastern coastal regions of the US, but the northern boundary of the native range is uncertain. Jenkins and Burkhead (1993) considered the fish native north to the Roanoke river, and probably introduced, but possibly native to the James River. They cite contradictory historical remarks, supporting an early introduction from South Carolina, or early occurrences (1820s) in the James. It was not found in pre-European or 17th century archaeological sites in Virginia (Miller 1986). The earliest verified specimen from a James River tributary was captured near Richmond in 1867 (Cope 1869). Other first records in major northeastern rivers are the Potomac (1876), Susquehanna (before 1893), Delaware (1880), Hudson (1827–1882); Connecticut (1850); Kennebec River (1940s); Penobscot River (1994). Possible vectors for these many separate introductions include the Erie Canal (for the Hudson), USFC stocking, state fisheries agencies, and private individuals.

In the Chesapeake Bay, as noted above, Largemouth Bass were probably introduced to the James River in the early 1800s. In the York River system, the first verified record of Largemouth Bass occurred in 1879 (Jenkins and Burkhead 1993). In 1892–1900, it was collected in the tidal Mattaponi River (Evermann and Hildebrand 1910). In the Rappahannock River, the fish was probably introduced by unofficial stocking before 1876 (Jenkins and Burkhead 1993) or by United States Fish Commission (USFC) stocking in 1894 and 1897 (Bean 1896; Ravenel 1898), but the first verified record was in 1951 (Jenkins and Burkhead 1993). Largemouths were widespread in the upper, middle and lower (tidal fresh) river by 1983 (Maurakis et al. 1987). The earliest Potomac specimen of M. salmoides was collected in 1876 (Bean and Weed 1911), and probably originated from unofficial stocking. It was introduced in Shenandoah River in 1889 and was later planted in the lower Potomac by the USFC . 'By 1896 the fish had become remarkably abundant in the vicinity of Washington' (Smith and Bean 1898). It is found from Chain Bridge to the Wicomico River and St. Clements Bay, but is more abundant in the tributaries (Lippson et al. 1979). Abundance of Largemouth Bass have greatly increased since the invasion of Hydrilla verticillata (Hydrilla) in the 1980s (Killgore et al. 1989; Phelps 1994).

In the Susquehanna River, official USFC stocking began there in 1893 (Worth 1895), but this fish was already 'widely introduced in Pennsylvania' (Bean 1893). Largemouth Bass were planted at Principio Creek in 1893 (Worth 1895), and the Severn, Gunpowder, Sassafras, Patapsco Rivers by United States Fish Commision in 1901–1910 (Ravenel 1902; Bowers 1912). The first verified captures from the Upper Bay were in Elk and Bohemia Rivers (Fowler 1917; Radcliffe and Welsh 1917). It occurs regularly in the Rhode River (Hines et al., unpublished data) and is widespread in upper Bay tributaries (Bush, Gunpowder, Northeast, Elk, Bohemia) (Fewlass 1980). In 1971–72, after heavy rains, including Hurricane Agnes, it was caught at Calvert Cliffs (Academy of Sciences of Philadelphia 1973), but was not collected there in subsequent (9) annual fish surveys (Horwitz 1987).

In the Delaware River Basin, Largemouth Bass were stocked by the state fisheries agency in five Pennsylvania counties, including Philadelphia in 1880 (Creveling 1881) and was probably introduced before 1893, since it was 'widely introduced in Pennsylvania' (Bean 1893). Pond rearing began in Wilmington, Delaware in 1891 (Raasch and Altemus 1991), and this fish was common at Millsboro Delaware (Fowler 1911). It is now widespread in fresh-oligohaline waters of the estuary (Horwitz 1986; Raasch and Altemus 1991; Weisberg 1996)

Dekay (1843) described a Black Bass, the 'Black Huron' ('Huro nigricans', probably M. salmoides), from the Great Lakes, but did not report it from the Hudson River. The first verified record from the Hudson was in 1882. The Erie Canal is a likely vector for the Largemouth Bass, although stocking cannot be ruled out (Daniels 2001; Daniels et al. 2005). Breeding populations of Largemouth Bass occur in coves and bays of the Hudson from Peekskill, near the limit of saltwater intrusion, to the head of tide at Troy (Nack et al.1993).

Largemouth Bass were released in Connecticut in 1850, probably from stock taken from Oswego Lake, New York, and probably in or near the Connecticut River in the Hartford area. By 1968, it was distributed in all of Connecticuts' major rivers, including the tidal regions of the Housatonic, Connecticut, Thames, and Pawcatuck, flowing into Long Island Sound (Whitworth et al. 1968; Whitworth 1996). In the Connecticut River, it was common near a power plant at East Haddam, near the limits of brackish-water penetration (Marcy 1966). In a 1988–1992 survey in the mainstem of the Connecticut River, they ranked 4th in abundance (Jacobs et al. 2004). Largemouth Bass occur in the upper 5 km of the Thames estuary, Norwich, Connecticut (Whitworth et al. 1980). Largemouth Bass are found in brackish-water estuaries, such as the Pettaquamscutt River (Horton 1958), and the upper reaches of Narragansett Bay (Marine Research Inc. 1992), possibly washed down from the freshwater reaches.

The Kennebec and Androscoggin Rivers in Maine, form the large, tidal freshwater Merrymeeting Bay, an important site for waterfowl and fisheries. Largemouth Bass were introduced to the Belgrade Lakes, in the central part of the Kennebec drainage (Kennebec River Council 1999). The Penobscot River, further north, is cooler, and may be less suitable. Largemouth Bass were first collected in lakes in the Penobscot drainage in 1994, and reported in the estuary by O'Malley et al. (2010).

Invasion History in Hawaii:

Largemouth Bass were first brought to Hilo, Hawaii in 1897. Another shipment was brought to Oahu in 1908, and a third to Kauai in 1911. Additional stockings have occurred in Hawaii. Largemouth Bass are established in reservoirs on all the main islands (Brock 1960; Lever 1996).

Invasion History Elsewhere in the World:

Largemouth Bass have been widely introduced in the interior of North America, to 34 US states, 5 Canadian provinces, and Mexico (Lever 1996; Brown et al. 2011). In eastern Canada, its range is shifting northward, due to a combination of natural dispersal, climate change, and human introductions (Alofs and Jackson 2015). Largemouth Bass have been reported from 70 countries worldwide (Food and Agriculture Organization 2018).

Largemouth Bass was introduced to Puerto Rico in 1915–1916, with another shipment in 1946. This fish is established in reservoirs all over the island (Lever 1996; USGS Nonindigenous Aquatic Species Program 2018). Largemouth Bass have also been introduced to Cuba, successfully, and Haiti (success unknown). Introduced populations in Honduras, Panama, Guatemala, Colombia, and Ecuador have become established in mountain lakes. Several introductions failed to establish in Lake Gatun, on the Panama Canal in 1917–1925, apparently because of high temperatures and native predators (Lever 1996). Largemouth Bass are established in the Igacu River, southern Brazil (Daga et al. 2016).

Largemouth Bass are successfully established in lowland rivers and lakes in Portugal (1952), Spain (1955), France (1877–1889), Cyprus (1971), and Italy (1890), but have much more limited populations (England. Belgium, Austria, Germany, Hungary), in northern Europe (Lever 1996). Largemouth Bass were introduced to Japan in 1925, in Lake Ashino-ko, Honshu, and is now established on all the major Japanese islands except Hokkaido, and based on modeling, is likely to survive on the lower elevations of that island. Much of the dispersal has been due to unofficial releases by anglers (Iguchi et al. 2014). In Africa, Largemouth Bass are established in 10 countries, but are most widespread and ecologically important in South Africa. They were introduced from Netherland hatchery stocks in 1927, and stocked in many of the coastal rivers of the southern, eastern, and western Cape (de Moor 1996; Lever 1996). The widely introduced stock was found to be genetically identical to a hatchery stock from Maryland (Hargrove et al. 2017). In 1980, fish of the Florida Largemouth Bass subspecies (M. s. floridanus subspecies were introduced to South Africa, because of their faster growth and greater longevity. Mitochondrial DNA of M. s. floridanus was found at 13 of 20 localities sampled across South Africa (Weyl et al. 2011). In Madagascar, Largemouth Bass are established in several mid-elevation and high plateau lakes (Lever 1996).

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Description

Largemouth Bass (Micropterus salmoides) is a large predatory freshwater fish, which often enters brackish water. Fishes of the genus Centrarchidae (Sunfishes and Black Basses) have a laterally compressed body. They have a spiny and a soft dorsal fin, which are fused. They have 3–8 anal spines, thoracic pelvic fins, and ctenoid scales. Largemouth Bass are largest of the Black Basses, moderately laterally compressed, with an elongated body and a large mouth, with the upper jaw extending well past the eye. The base of the anal fin is less than half the length of the dorsal fin. The tail fin is shallowly forked (Page and Burr 1991; Jenkins and Burkhead 1993). The Largemouth Bass is somewhat streamlined but robust, with the dorsal profile of the head slightly convex. The spiny and anal dorsal fins are nearly separate. There are 58–72 lateral line scales, 9–12 dorsal spines, 11–14 dorsal rays, 3 anal spines, and 11–12 anal rays. Record fish range from 760 to 970 mm, but a more usual large size is ~400–450 mm. The body is silvery to grassy-green above (brown in dark water), with dark mottling, on the back and white below. A dark side along the side runs from the snout to the tail, often broke up into dark blotches (Page and Burr 1991; Jenkins and Burkhead 1993; Moyle 2002).

The Florida Largemouth Bass (M. s. floridanus) is genetically distinct and is known to grow faster, reach larger sizes and live longer than the widely distributed, northern populations (M. salmoides), and is sometimes treated as a full species. It has been stocked in California reservoirs, South Africa, and elsewhere (Dill and Cordone 1997; Weyl et al. 2017). A very recent revision of the genus Micropterus treats the Florida Largemouth Bass as the typical form of M. salmoides , and names the more widespread and more widely introduced northern form as M. nigricans (Kim et al. 2022). In this account, we will treat all the 'Largemouth Bass' populations as M. salmoides.  In the 19th century, 'Black Basses', (Smallmouth and Largemouth) were frequently confused, especially when transported for stocking (Smith 1895), or in distributional records. Consequently, there is often some uncertainty over whether the first 'Black Bass' introduced to an estuary was Smallmouth or Largemouth.

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Taxonomy

Ecology

General:

The Largemouth Bass (Micropterus salmoides) is a freshwater predatory fish, which frequently enters brackish water. Adults can mature at 1 to 4 years, depending on latitude, at sizes of 140–254 mm (Hardy 1978; Jenkins and Burkhead 1993; Moyle 2002). Spawning takes place at 12–26 °C, in freshwater. Adult male fish move into shallow water, ~0.3–0.6 m deep, near shore, and excavate a nest in sand, gravel, or mud, often sheltered by logs, roots, or vegetation (Hardy 1978; Wang 1986; Nack et al.1993; Jenkins and Burkhead 1993; Moyle 2002). Males guard a nesting site against other males, and court females. Females may spawn with more than one male, and males may spawn with more than female. Females can carry 2000–145,000 eggs. Males vigorously guard the eggs through hatching, to the postlarval stage. Eggs take 2–5 days to develop at 12–24 °C. The postlarvae swim in schools in shallow, weedy waters (Hardy 1978; Wang 1986; Jenkins and Burkhead 1993; Moyle 2002). Adults in Virginia typically live for 8–10 years, but one specimen in Indiana lived for 16 years (Jenkins and Burkhead 1993).

Largemouth Bass inhabit clear, vegetated lakes, ponds, swamps, backwaters and pools and creeks of small to large rivers, often associated with logs, brush and roots (Hardy 1978; Page and Burr 1991; Wang 1986). Largemouth Bass are abundant in vegetated tidal freshwater and oligohaline estuaries (Murdy et al. 1997). Preferred temperatures are 26–28 °C, but Largemouth Bass have been collected at 5 °C and have an experimental upper lethal temperature of 37 °C (Hardy 1978). On the Gulf and East coasts, Largemouth Bass utilize brackish wetlands. They have been collected at salinities as high as 12.9 PSU in the Chesapeake Bay (Hildebrand and Schroeder 1928). In the laboratory, fish were stressed and stopped eating at 12 PSU (Meader and Kelso 1990). In preference tests, fish preferred salinities of less than 3 PSU (Meador and Kelso 1989). However, fish were caught in Mobile-Tensaw Delta even in times of elevated salinity (4–15 PSU) (Norris et al. 2005). In the San Francisco Bay Delta, Largemouth Bass appear to be rare in brackish water (Wang 1986; Matern et al. 2002). Largemouth Bass tolerates dissolved oxygen of .9–1.0 ppm at 21 °C, but is usually associated with well-oxygenated waters (Carlander 1977). Juveniles feed on microcrustaceans and insects, and small fishes switch to larger fish and crayfish as they grow. Adults feed mostly on fishes. In East Coast and Gulf estuaries, Blue Crabs (Callinectes sapidus) are common prey (Glover et al. 2013). Other prey include amphibians, insects, and other Largemouth Bass (Jenkins and Burkhead 1993; Moyle 2002). In the Delta, the most common prey were insects, amphipods, shrimp, Spiny Sculpin (Cottus asper, native), Mississippi Silverside (Menidia audens, introduced), Lepomis spp. (Sunfishes), and Yellowfin Goby (Acanthogobius flavimanus). The Smallmouth (M. dolomieu) and Spotted Bass (M. punctulatus) are potential competitors, but largely prefer different habitats (Moyle 2002). Humans are the primary predators of adult fish (Weinersmith et al. 2019). The Largemouth is an esteemed gamefish (Jenkins and Burkhead 1993; Moyle 2002).

Food:

insects, crayfishes, fishes

Consumers:

fishes, birds, humans

Competitors:

Smallmouth Bass, Spotted Bass; Striped Bass

Trophic Status:

Carnivore

Carn

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Habitats

General Habitat	Nontidal Freshwater	None
General Habitat	Fresh (nontidal) Marsh	None
General Habitat	Tidal Fresh Marsh	None
General Habitat	Swamp	None
General Habitat	Grass Bed	None
General Habitat	Coarse Woody Debris	None
General Habitat	Rocky	None
General Habitat	Salt-brackish marsh	None
General Habitat	Unstructured Bottom	None
General Habitat	Canals	None
Salinity Range	Limnetic	0-0.5 PSU
Salinity Range	Oligohaline	0.5-5 PSU
Salinity Range	Mesohaline	5-18 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Nektonic	None

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Life History

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	0.6	Field (Hardy 1978)
Maximum Temperature (ºC)	36.4	Experimental (Hardy 1978)
Minimum Salinity (‰)	0	This is a freshwater species.
Maximum Salinity (‰)	12	Field records up to 32 PSU have been reported (Hardy 1978), but salinities above 12 PSU are lethal in long-term (90 day) laboratory experiments (Meador and Kelso 1990).
Minimum Dissolved Oxygen (mg/l)	1.5	usually avoiding levels below 3 (Brown et al. 2009)
Minimum pH	5.1	Field (Hardy 1978)
Maximum pH	10.2	Field (Hardy 1978)
Minimum Reproductive Temperature	12.2	Field (Hardy 1978)
Maximum Reproductive Temperature	25.5	Field (Hardy 1978)
Minimum Reproductive Salinity	0	This is a freshwater species.
Maximum Reproductive Salinity	5	Field (Meador and Kelso 1989)
Minimum Length (mm)	285	Hardy 1978
Maximum Length (mm)	648	Hardy 1978

General Impacts

Largemouth Bass (Micropterus salmoides) is a large predatory freshwater fish, which has been widely introduced around the world as a gamefish. It has been introduced to drainages in 34 states, 3 Canadian provinces, and 70 foreign countries (Brown 2009a; Food and Agriculture Organization 2018; USGS Nonindigenous Aquatic Species Program 2018). In tidal estuaries, such as the San Francisco, Columbia, Chesapeake, Delaware, Hudson, and others, it supports major sport fisheries, bass tournaments, specialized bass boats, and much economic activity. It is a major predator in the rivers to which it is introduced, but in addition, in West Coast rivers and reservoirs, non-native forage fishes were introduced to support the bass stocks, creating equal or larger impacts to the bass themselves (Cohen and Carlton 1995; Dill and Cordone 1997). Introductions of M. salmoides in and outside North America have occasionally had severe effects on native fishes, fisheries, and other aquatic wildlife (Lever 1996; Brown et al. 2009a)

Economic Impacts

Largemouth Bass have been introduced worldwide, and is a highly prized sportfish wherever it is found (Jenkins and Burkhead 1993; Moyle 2002; Lever 1996). It is one of the most important gamefishes in North America, both within its native range, and in its introduced range. It is native or established in every US state except Alaska (USGS Nonindigenous Aquatic Species Program 2018). Initially, introduced Largemouth Bass were harvested commercially, but became legally designated as a game fish by 1915 in Oregon (Lampman 1946), by 1945 in Maryland (Fewlass 1980), and probably elsewhere. Bass fishing, largely for the Largemouth, has become a major part of American culture, and the recreational economy. It supports tournaments, specialized bass boats, and television shows, as well as millions of anglers and fishing trips. Overall, sports fishing supported $48 billion in retail sales in 2011 and contributed $115 billion to the national economy (American Sportfishing Association 2015), and the Largemouth Bass fishery constitutes a large fraction of that spending. In a survey of 1780 anglers in the San Francisco Delta complex, 30% of anglers reported fishing for 'Black Bass', dominated by Largemouths. Total value of sportfishing in the Delta for 6 major fishes (including 'Black Bass) was estimated at $470,280,821 (The Program for Applied Research and Evaluation, California State University 2013). Web searches indicate that major sport fisheries for Largemouth Bass, including tournaments, occur in the tidal regions of the San Francisco estuary, the Columbia River, Chesapeake Bay, the Delaware River estuary, the Hudson River, and the Connecticut River.

Ecological Impacts

Predation- Largemouth Bass (Micropterus salmoides) is one of the major predators in its native and introduced lakes, rivers, and estuaries. Because of the early date of its introduction, and its introduction with several other predatory and competitive fishes, it plays a large role in the decline or extinction of native species. Jenkins and Burkhead (1993) and others have suggested the introduction of large predatory fishes, primarily Largemouth Bass, Smallmouth Bass (M. dolomieu), and Channel Catfish (Ictalurus punctatus), may have been responsible for the extinction of two small benthic fishes, Logperch (Percina caprodes) in the Potomac; and Troutperch (Percopsis oniscomaycus) in the entire Chesapeake drainage. In the San Francisco estuary, predation by Largemouth Bass played a possible role in the extinction of Thicktail Chub (Gila crassicauda), and the decline of Sacramento Perch (Archoplites interruptus (Cohen and Carlton 1995). In the southwest United States (California and Arizona), predation by Largemouth Bass has had negative impacts on native populations of trout, minnows, pupfish (Cyprinodon), and topminnows (Gambusia spp., Poecilopsis spp.), particularly on isolated populations of desert fishes such as the Owens Tui Chub (Gila bicolor snyderi ) (Dill and Cordone 1997).

In the Pacific Northwest, predation by bass on juvenile salmon and steelhead (Oncorhynchus spp.) in lakes and streams is a major concern, In one study of lakes in the Puget Sound watershed, Largemouth Bass were responsible for 98% of predation on wild juvenile Coho Salmon (O. hisutch) (Bonar et al. 2005). In another study of Largemouth Bass diet, 31 of 280 bass contained salmonid smolts (Tabor et al. 2004, cited by Brown et al. 2009). Experimental removal of predators, dominated by Largemouth Bass, increased the survival of tagged Chinook Salmon (Oncorhynchus tshawytscha) migrating through the North Fork Mokelumne River, at the edge of the Delta (Cavallo et al. 2013). Caging experiments indicate that predation on Chinook Salmon by Largemouth Bass was greatest in the presence of submerged aquatic vegetation, such as Brazilian Waterweed (Egeria densa, now abundant in the Delta (Zeug et al. 2020). Brown et al. (2009) suggest that the biggest effect of Largemouth Bass predation may be to interfere with recovery of salmonid stocks from overfishing and habitat disturbance.

In South Africa, Largemouth Bass have been responsible for the decline of several native fishes, including the minnows the genus Barbus (Lever 1996). In some smaller headwater streams, Largemouth Bass had eliminated all the native fish species (Weyl and Ellender 2014). In the estuary of the Kowie River, they were eating several species of marine fishes that use the river as a nursery (Magoro et al. 2015). Overall, the Largemouth Bass is considered have the largest negative impact of any piscivorous fish introduced to South Africa (Lever 1996).

Introduction of gamefish, particularly the Largemouth Bass to reservoirs, has involved creating or reconstructing the foodweb by introducing forage fishes. These small fishes have dispersed downstream and have had impacts equal to or exceeding those of the bass. In Chesapeake Bay and estuaries of the southeast Atlantic Coast, the principal example is the Threadfin Shad (Dorosoma petenense). In San Francisco Bay, introduced forage fishes include Threadfin Shad, Golden Shiner (Notemigonus chrysoleucas, and Bluegill (Lepomis macrochirus) (Moyle 2002).

Competition - Competition is possible between Largemouth Bass (Micropterus salmoides) and Smallmouth Bass M. dolomieu. The two species differ in mouth size and habitat preference. The history of the two species in Chesapeake Bay is suggestive of competition. Smallmouth Bass was introduced to the Potomac first, and rapidly colonized the Potomac down to Mount Vernon but soon became rare in tidal waters below Washington D.C. (Smith 1907), coinciding with the introduction of M. salmoides which rapidly became abundant in tidal waters (Smith and Bean 1898). Both species are largely piscivorous as adults, but Largemouth Bass appears to have a much greater preference for still water, vegetation, and for estuarine conditions (Hildebrand and Schroeder 1928; Jenkins and Burkhead 1993; Page and Burr 1991). When kept in aquaria together, Smallmouth Bass select smaller prey than Largemouth Bass of similar size, and are more likely to capture prey near the substrate, while Largemouth Bass are more likely to feed in the water column (Winemiller and Taylor 1987).

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Regional Impacts

P090	San Francisco Bay		Ecological Impact	Predation
The Largemouth Bass, together with the Smallmouth Bass (M. dolomieu), and Channel Catfish (Ictalurus punctatus), has a possible role in extinction of Thicktail Chub (Gila crassicauda) and the decline of Sacramento Perch (Archoplites interruptus) (Cohen and Carlton 1995) in the San Francisco estuary watershed. Experimental removal of predators, dominated by Largemouth Bass, increased the survival of tagged Chinook Salmon (Oncorhynchus tshawytscha) migrating through the North Fork Mokelumne River, at the edge of the Delta (Cavallo et al. 2013). Largemouth Bass are now the most abundant piscivorous fish in the San Francisco Estuary Delta. Major prey items include Red Swamp Crayfish (Procambus clarkii) and non-native centrarchids, but predation on native fishes is also a concern (Weinersmith et al. 2019). Caging experiments in the Delta indicated that predation on Chinook Salmon was greatest in enclosures with submerged aquatic vegetation (Zeug et al. 2020).
M090	Delaware Bay		Ecological Impact	Predation
Micropterus salmoides (Largemouth Bass) is a major predator in Delaware River estuary. Introduction of this and other large piscivorous fishes may have decreased the abundance both of native prey species and the two major piscivores in the estuary, Esox niger (Chain Pickerel) and Morone saxatilis (Striped Bass). However, evidence for this is scanty (Horwitz 1986).
M090	Delaware Bay		Economic Impact	Fisheries
Largemouth Bass (Micropterus salmoides is a major gamefish in the Delaware River, and the surrounding watershed (Raasch and Altemus 1991). Web searches indicate that several bass tournaments were scheduled along the tidal river in 2018.
M130	Chesapeake Bay		Ecological Impact	Predation
Prey of Largemouth Bass in upper Chesapeake Bay included Gizzard Shad (Dorosoma cepedianum), Cyprinidae and Cyprinodontidae ('minnows'), Inland Silverside (Menidia beryllina), White Perch (Morone americana), Yellow Perch (Perca flavescens), and darters (Etheostoma) spp. (Fewlass 1980). 'The contents of 22 stomachs taken in brackish water consisted exclusively of fish remains. This fish is highly predatory; and where it is common, the destruction of minnows and smaller fish is great' (Hildebrand and Schroeder 1928).
M130	Chesapeake Bay		Economic Impact	Fisheries
Fisheries - Largemouth Bass (Micropterus salmoides) is a major sportfish in upper Chesapeake Bay and in all fresh-oligohaline tributaries of the Bay. Largemouth Bass were harvested commercially from Maryland tidal fresh and brackish waters of Chesapeake Bay until 1945, when it was designated a sportfish. Sportfishing pressure was initially low but intensified in the 1960's and 70's, resulting in lower abundances in MD tidewaters (Fewlass 1980). In the tidal Potomac, especially since the resurgence of submerged aquatic vegetation (SAV), and in other low-salinity regions, this fish attracts many fishers who make substantial investments in boats, tackle, and fishing tournaments. In 1998, 4 tournaments were held on tidal waters of the Bay (American Bass Association 1998). Similar bass tournaments on one location of the Hudson River generated $2.5 million/year (Mills et al. 1996a), so it is likely that Largemouth Bass contributes millions of dollars annually to local economies.
M060	Hudson River/Raritan Bay		Economic Impact	Fisheries
The tidal Hudson River has developed a rapidly growing sport fishery, mostly centered on tournaments, since the 1970s (Nack et al. 1993).
P090	San Francisco Bay		Economic Impact	Fisheries
In a survey of 1780 anglers in the San Francisco Delta complex, 30% of anglers reported fishing for 'Black Bass', dominated by Largemouths. Total value of sportfishing in the Delta for 6 major fishes (including 'Black Bass) was estimated at $470,280,821 (The Program for Applied Research and Evaluation, California State University 2013). We do not have the data to subdivide this figure, but indcates a substantial value for the Largemouth Bass sport fishery.
M130	Chesapeake Bay		Ecological Impact	Competition
Competition is possible between Largemouth Bass and Smallmouth Bass (M. dolomieu) which was probably introduced first to the Potomac. Smallmouth Bass rapidly colonized the Potomac down to Mount Vernon but soon became rare in tidal waters below Washington D.C. (Smith 1907). This range contraction coincides with the introduction of Largemouth Bass which rapidly became abundant in tidal waters (Smith and Bean 1898). Both species are largely piscivorous as adults, but M. salmoides appears to have a much greater preference still water, vegetation, and for estuarine conditions (Hildebrand and Schroeder 1928; Jenkins and Burkhead 1993; Page and Burr 1991).
P023	_CDA_P023 (San Louis Rey-Escondido)		Ecological Impact	Predation
Largemouth Bass were removed from the San Mateo Creek Lagoon when caught in seines, as a threat to native fishes, particularly the Southern Tidewater Goby (Eucyclogobius kristinae) (Spies 2022)
CA	California		Ecological Impact	Predation
The Largemouth Bass, together with the Smallmouth Bass (M. dolomieu), and Channel Catfish (Ictalurus punctatus), has a possible role in extinction of Thicktail Chub (Gila crassicauda) and the decline of Sacramento Perch (Archoplites interruptus) (Cohen and Carlton 1995) in the San Francisco estuary watershed. Experimental removal of predators, dominated by Largemouth Bass, increased the survival of tagged Chinook Salmon (Oncorhynchus tshawytscha) migrating through the North Fork Mokelumne River, at the edge of the Delta (Cavallo et al. 2013). Largemouth Bass are now the most abundant piscivorous fish in the San Francisco Estuary Delta. Major prey items include Red Swamp Crayfish (Procambus clarkii) and non-native centrarchids, but predation on native fishes is also a concern (Weinersmith et al. 2019). Caging experiments in the Delta indicated that predation on Chinook Salmon was greatest in enclosures with submerged aquatic vegetation (Zeug et al. 2020). , Largemouth Bass were removed from the San Mateo Creek Lagoon when caught in seines, as a threat to native fishes, particularly the Southern Tidewater Goby (Eucyclogobius kristinae) (Spies 2022)
CA	California		Economic Impact	Fisheries
In a survey of 1780 anglers in the San Francisco Delta complex, 30% of anglers reported fishing for 'Black Bass', dominated by Largemouths. Total value of sportfishing in the Delta for 6 major fishes (including 'Black Bass) was estimated at $470,280,821 (The Program for Applied Research and Evaluation, California State University 2013). We do not have the data to subdivide this figure, but indcates a substantial value for the Largemouth Bass sport fishery.

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