John Lyons, Wisconsin Department of Natural Resources
Publication Date - April 2011
|Common Name:||Smallmouth Bass|
|Other Common Names:||Small-mouthed bass, smallmouth black bass, smallmouth, northern smallmouth bass, SMB, bronzeback, redeye bass, red-eye (Waukesha County–Cahn 1927), and yellow bass (Madison lakes–Schneberger 1977). Jordan et al. (1930), Becker (1983), Cloutman and Olmstead (1983), and Tomelleri and Eberle (1990) list over 30 other common names used outside of Wisconsin.|
|Scientific name:||Micropterus dolomieu|
|Wisconsin Synonyms:||Micropterus salmoides (error) (Hoy 1883)|
Micropterus dolomieui (Becker 1983 and many publications from ~1960 to 1990)
|Etymology:||Micropterus – Greek, meaning small fin|
dolomieu – after M. Dolomieu, a French mineralogist and friend of Lacépède, who described the species
The smallmouth bass is a member of the sunfish family Centrarchidae and was described by Lacépède in 1802 from an unknown location, presumably somewhere in eastern North America. Recent analyses of relationships among the black basses (Micropterus) based on mictochondrial and nuclear DNA sequences indicate that the smallmouth bass is most closely related to the spotted bass (M.punctulatus), a species found in the eastern United States south of Wisconsin (Kassler et al. 2002; Near et al. 2003, 2004).
Substantial morphological and genetic variation exists among smallmouth bass populations across its native range. As part of their revision of the black basses, Hubbs and Bailey (1940) recognized two subspecies of smallmouth bass, M. dolomieu dolomieu, the northern smallmouth bass, found in Wisconsin and most of the rest of the species’ range, and M. dolomieu velox, the Neosho smallmouth bass, limited to the Neosho River drainage of the Arkansas River basin in the southwestern Ozark Mountains of Missouri, Arkansas, and Oklahoma. Intergrades between the two subspecies were thought to occur in other drainages of the Ozark Mountains of southern Missouri and northern Arkansas and in the Ouachita Highlands of southwestern Arkansas and southeastern Oklahoma. However, the validity of these subspecies and intergrades has long been questioned (Ramsey 1975; Kassler et al. 2002). A recent genetic analysis using allozymes, including a Wisconsin population from Mineral Point Branch in Iowa County, supports the distinctiveness and broad distribution of the northern smallmouth bass relative to the Neosho smallmouth bass (Stark and Echelle 1998). However, among the presumed intergrades, the populations in the southern Ozarks are similar to the northern smallmouth bass, and the Ouachita Highland populations are distinct from both the northern and Neosho forms.
Another study examined genetic variation among smallmouth bass populations within Wisconsin (Fields et al. 1997). Specimens from 19 locations throughout the state were analyzed with allozymes, mitochondrial DNA, and nuclear DNA. Genetic variation among populations was relatively low and did not have an easily interpretable geographic distribution. This perhaps reflected the relatively recent (in geologic terms) colonization of Wisconsin by smallmouth bass from a single refugium following the retreat of the glaciers of the last ice age as well as the numerous transplants of smallmouth bass around the state that have occurred over the last 120 years (Borden and Krebs 2009). However, there was some tendency for populations from the Great Lakes basin to differ from those of the Mississippi River basin (Fields et al. 1997).
Natural hybrids involving smallmouth bass are generally rare (Hubbs and Bailey 1940), and no hybrids involving smallmouth bass have been reported from Wisconsin. However, where smallmouth bass have been introduced outside of their native range or where another Micropterus species has been introduced into the smallmouth bass native range, hybrids involving smallmouth bass may occur. Introduced smallmouth bass hybridize with introduced and native largemouth bass (M. salmoides) and native Guadalupe bass (M. treculi) in Texas (Whitmore and Hellier 1988; Morizot et al. 1991). This hybridization has threatened the continued survival of the Guadalupe bass. Viable hybrid smallmouth-largemouth bass can also be produced by artificial fertilization (Childers 1975). Within the native range of smallmouth bass, introductions of spotted bass in Missouri (Koppelman 1994) and redeye bass (M. coosae) in Tennessee (Turner et al. 1991) led to hybridization and genetic introgression that decreased the viability of smallmouth bass populations.
In adult smallmouth bass, the body is moderately deep, with a maximum body depth of 28–35% of standard length (SL) (Hubbs and Bailey 1940), and somewhat laterally compressed, with a body width of 15–18% of SL. Total length (TL) equals 1.18 times SL (Bennett 1938).
Smallmouth bass have a relatively large, sub-triangular-shaped head, with a length of 32–37% of SL. The mouth is terminal and slightly oblique, and the lower jaw length is 53–57% of head length (HL). The posterior edge of the upper jaw extends to, but not beyond, the posterior portion of the eye, and the upper jaw length is 42–46% of HL.
The eye is relatively large and is 14–25% of HL. Pads of fine pointed teeth occur on the upper and lower jaws. The 11 or so gill rakers on the first arch are relatively long and straight, and the pharyngeal arch is narrow with many fine teeth (Becker 1983; Holland-Bartels et al. 1990). There are usually six or seven branchiostegal rays on each side of the head (Scott and Crossman 1973). The smallmouth bass has two dorsal fins, broadly joined, the anterior usually with 10 sharp spines and the posterior with 14 soft rays. The anal fin has three spines and usually 11 rays. The pectoral fins are relatively short and rounded with eight to nine rays each. The pelvic fins are located ventral to the pectoral fins and have one spine and five rays. The tail is slightly forked with rounded lobes. Scales are ctenoid, and all lateral line scales are pored. Counts of fin spines and rays, scales, and vertebrae are given in Table 1.
Table 1. Counts of fin elements, scales, and vertebrae for smallmouth bass from throughout their range (from Hubbs and Bailey 1940).
|Character||Median||Mean||Range||Number of specimens|
|First dorsal fin spines||10||9.98||9–11||229|
|Second dorsal fin rays||14||14.01||12–15||239|
|Anal fin spines||3||3.0||3–3||137|
|Anal fin rays||11||10.93||10–12||137|
|Pectoral fin rays||17||16.75||15–18||182|
|Scale rows above lateral line||13||12.41||11–13||61|
|Scale rows below lateral line||21||20.98||19–23||61|
|Lateral line scales||75||74.37||68–81||92|
|Scales around caudal peduncle||29||30.00||29–32||15|
|Scale rows on cheek||16||15.60||14–18||81|
Smallmouth bass adults vary in color, ranging from a lightly mottled or solid dark tan, brown, bronze, or olive color on the back and sides, grading to light yellow, cream, or white on the belly. Often there are about 10–15 dark but diffuse vertical bars on the sides of the body and three diffuse streaks on the head radiating back from the eye. Colors are more intense in breeding fish; nesting males may be blackish. The eye is red or orange. The fins generally are a uniformly pigmented tan, brown, olive, or cream and are similar in color to adjacent areas of the body. Ventral fins are often yellowish near their base.
Juvenile smallmouth bass have different color patterns than adults. The eggs are grayish white, light amber, or pale yellow with a golden oil globule (Holland-Bartels et al. 1990). Newly hatched larvae are largely transparent with a yellow or golden yolk sac and narrow stripes of dark pigment along the body. As the larvae grow to about 9 mm TL they become increasingly pigmented until they are very dark (Fish 1932; Tin 1982), a stage at which they are typically called “black fry.” As they continue growing to about 25 mm TL, they begin to take on more adult-like color patterns (Reighard 1906). At 25–51 mm TL, they have a brownish olive body with 10 or more distinct dark vertical bars on the side. The three streaks radiating from the eye are also dark and pronounced. The tail is a light yellowish orange, often with a dark brown or black spot at the base and dark brown or black on the edges of each tail lobe.
By 102–127 mm TL the coloration of juvenile fish usually looks like that of the adult.
Among Wisconsin species, the smallmouth bass is most like the largemouth bass in appearance. The two species have a very similar shape and body plan, but several characteristics readily distinguish them (Hubbs and Bailey 1940). The smallmouth bass, not surprisingly, has a smaller mouth than the largemouth bass. In the smallmouth bass, the posterior end of the upper jaw extends back as far as the posterior half of the eye but never beyond the posterior edge of the eye. Conversely, the posterior end of the upper jaw of the largemouth bass extends to or beyond the posterior edge of the eye. In the smallmouth bass, the longest spine of the dorsal fin is less than half as tall as the longest dorsal ray, and the spiny and soft lobes (rays) of the dorsal fin are well connected by a membrane. Pulling the spiny lobe erect will cause the soft lobe to become erect as well. In the largemouth bass, the longest dorsal spine is more than two-thirds the length of the longest dorsal ray, and the two dorsal lobes are weakly connected. Pulling the spiny lobe erect will not elevate the soft lobe. The smallmouth bass tends to have 10 or more diffuse dark vertical bars on the side whereas the largemouth bass has a blotchy irregular black horizontal lateral stripe. The smallmouth bass has smaller and more numerous scales: 68–81 in the lateral line, 11–13 above the lateral line, 19–23 below the lateral line, and 14–18 rows on the cheek, versus 58–69, 7–9, 14–17, and 9–12, respectively, in the largemouth bass. See http://www.seagrant.wisc.edu/home/Default.aspx?tabid=604 for more details and photos to aid in the identification of the smallmouth bass.
Compared to other Wisconsin game fish, the smallmouth bass reaches medium size and moderate age. Typical adult size ranges from 200 to 400 mm TL and age ranges from 3 to 7. In Wisconsin, smallmouth bass above 483 mm TL and 1.6 kg are rare. The state angling record, caught in 1950 from Indian Lake, Oneida County, is 4.1 kg (9 lb, 1 oz). Male smallmouth bass typically mature at an age of 3–5 years and a size of 204–279 mm TL (Becker 1983; Raffeto et al. 1990; Wiegmann et al. 1992, 1997). Although reproductive females may be as young as three years and as small as 204 mm TL, more typically, female smallmouth bass mature at an age of 4–7 years and a size of 254–380 mm TL (Latta 1963; Wiegmann et al. 1992). Faster growing fish mature at an earlier age (Dunlap et al. 2005a). The maximum reported age, based on scales, in smallmouth populations from Wisconsin and surrounding states is 14–15 years, but fish over 10 are scarce (Bennett 1938; Marinac-Sanders and Coble 1981; Forbes 1989; WDNR, unpublished data). Smallmouth bass older than 16 years have been found in southern Ontario (Cooke et al. 1998). Ages determined from scales tend to underestimate true smallmouth bass age, particularly in older fish (Heidinger and Clodfelter 1987), so maximum age estimates for Wisconsin may be too low.
Growth in length varies among smallmouth bass populations in Wisconsin (Table 2). There can be substantial growth variation among nearby waters, but generally the slowest growing populations occur in infertile waters in northern Wisconsin, where the growing season is shortest, and the fastest growing populations are found in fertile waters in southern Wisconsin, where the growing season is longest. However, the slower growing populations often have the oldest fish. Growth is particularly variable in the first year of life, ranging among individuals by more than a factor of three, from 40 to 125 mm TL (Bennett 1938; Lyons 1997; WDNR, unpublished data). Growth generally does not differ between males and females (Bennett 1938).
Few data are available from Wisconsin on smallmouth bass growth in weight. Paragamian and Coble (1975) gave the following weights, back-calculated from scales, for the Red Cedar River, Dunn County, in 1972: age 1 – 0.012 kg; age 2 – 0.091 kg; age 3 – 0.291 kg; age 4 – 0.520k g; age 5 – 0.844 kg; age 6 – 1.02 kg; age 7 – 1.17 kg; age 8 – 1.35 kg. Serns (1984b) provided a table of weights at age for eight years in Nebish Lake, Vilas County. For the 1978–81 period in which a 204-mm (8-inch) TL minimum length limit for angling harvest was in place, the average measured weight at the beginning of the growing season was: age 1 – 0.009 kg; age 2 – 0.036 kg; age 3 – 0.109 kg; age 4 – 0.258 kg; age 5 – 0.575 kg; age 6 – 1.04 kg; age 7 – 1.17 kg; age 8 – 1.315 kg; age 9 – 1.35 kg.
If growth in length is known, growth in weight can be estimated from an equation that relates weight to length. However, only a few such equations have been published for Wisconsin. For Nebish Lake in 1980, this equation was log10(weight in lbs) = -3.532 + 3.123[log10(TL in inches)] (Serns 1984b). Kolander et al. (1993) derived the following overall equations for smallmouth bass larger than 150 mm (5.9 inches) TL from 50 populations throughout the United States: log10(weight in lbs) = -3.491 + 3.200[log10(TL in inches)] and log10(weight in g) = -5.329 + 3.200[log10(TL in mm)]. Four of the 50 populations were from Wisconsin: Galena River, Lafayette County: log10(weight, g) = -4.872 + 2.999[log10(TL, mm)]Little Platte River, Grant County: log10(weight, g) = -5.528 + 3.267[log10(TL, mm)]Mineral Point Branch, Iowa County: log10(weight, g) = -6.304 + 3.565[log10(TL, mm)]Wisconsin River, Sauk County: log10(weight, g) = -5.354 + 3.187[log10(TL, mm)]
Table 2. Total length (mm) at age, back-calculated from scales, for selected Wisconsin smallmouth bass populations.
|Total Length (mm) at age|
|73 lakes and rivers statewide, 1970s–1980s||WDNR, unpublished data||94||168||239||297||351||384||432||462||472||490|
|Lake Michigan/Green Bay, Door County||Wiegert 1966||66||124||185||236||277||315||356||384||409||427||432|
|Ike Walton Lake, Vilas County||Bennett 1938||61||124||193||246||295||323||353||401||427||447||467|
|Clear Lake, Oneida County||Marinac-Sanders and Coble 1981||92||142||185||240||297||354||394||427||453||473||497|
|Trout Lake, Vilas County||Bennett 1938||53||152||231||325||366||394||411||427||442||455||462|
|Galena River, Lafayette County||Forbes 1989||–||173||239||302||368||394||424||445|
|Red Cedar River, Dunn County||Paragamian and Coble 1975||100||190||274||329||383||407||424||444|
|Lake Geneva, Walworth County||Mraz 1960||71||173||277||356||409||452||478|
|Wisconsin River, Sauk County||WDNR, unpublished data, 1987||–||148||278||387||436||463||480||495|
|19 northern lakes, 1930s||Bennett 1938||58||135||206||272||328||363||394||424||455||457||467|
|16 central and southern rivers, 1950–1980s||Forbes 1985||89||178||246||307||353||396||432||452||475|
Smallmouth bass growth is driven primarily by the amount of food available, which dictates how much mass the fish can accumulate, and water temperature, which determines the rates of consumption, respiration, and other metabolic processes necessary for growth (Shuter and Post 1990; Lyons 1997; Whitledge et al. 2002). Generally, smallmouth bass grow more slowly in lakes with low densities and smaller sizes of prey than in lakes with high densities and larger sizes (Clady 1977; Dunlap et al. 2005b). In a northeastern Iowa stream (Paragamian and Wiley 1987) and a southeastern Ohio stream (Brown 1960), smallmouth bass growth was best at intermediate flows and was reduced during years with droughts or numerous floods. Flow extremes were thought to reduce invertebrate food availability. In Illinois streams, smallmouth bass growth was correlated with the amount of cobble substrate, which in turn was likely related to the relative amount of food available (Putnam et al. 1995). When food is unlimited, sub-adult and adult smallmouth bass grow fastest at 22°C (Whitledge et al. 2002). In northern Wisconsin lakes, smallmouth bass growth was greater in warmer than in cooler summers (Serns 1982; Hoff and Serns 1990). In cold climates, such as in northern Ontario or in high-elevation reservoirs in the western United States, low summer temperatures and a short growing season result in particularly slow smallmouth bass growth rates (Shuter and Post 1990; Patton and Hubert 1996). Slow growth of young-of-year fish may limit the distribution of smallmouth bass, as these fish may not be able to store enough energy during their first growing season to survive their first winter (Shuter and Post 1990; Lyons 1997; Curry et al. 2005).
The native range of the smallmouth bass encompasses most of the Great Lakes, upper Mississippi River, and Ohio River basins plus some tributaries of the lower Missouri and lower Mississippi basins (Robbins and MacCrimmon 1974). This range stretches from northern Minnesota, Ontario, and Quebec in the north to northern Alabama, southern Arkansas, and extreme southeastern Oklahoma in the south and from eastern South Dakota in the west to western Vermont and Quebec in the east.
The smallmouth bass has been widely introduced, and its current range is much broader than its native range (Robbins and MacCrimmon 1974; Lee 1980). Smallmouth bass are now distributed on the Atlantic slope of the United States and Canada from Georgia to Newfoundland. Populations are established in the Lake Winnipeg drainage (Hudson Bay basin) of northern Minnesota, northwestern Ontario, southern Manitoba, and North Dakota. Successful transplants have been made into the waters of all states west of the Mississippi (including Hawaii) except for Alaska and Louisiana. Smallmouth bass are particularly common in the Columbia and Snake rivers of Washington, Oregon, and Idaho. Introductions have also been made outside of North America in temperate regions of South and Central America, Oceania, eastern Asia, southern Africa, and Europe, but the only established populations appear to be in South Africa, Zimbabwe, Finland, Denmark, and France (Skelton 1993; Miller and Loates 1997).
Smallmouth bass are common in lakes and rivers throughout Wisconsin (Fago 1992; Lyons et al. 2000).
Most authors indicate that the species was native to all parts of the state (e.g., Greene 1935; Hubbs and Bailey 1938; Becker 1983). However, Robbins and MacCrimmon (1974) provide compelling arguments that smallmouth bass were not originally found in the inland portion of the Lake Superior basin, although they occurred in warmer bays of the lake proper and the lower reaches of the larger and warmer tributaries. Apparently, waterfalls and other natural barriers prevented smallmouth bass from colonizing most of the basin following the retreat of the glaciers. However, by the early 1900s humans had introduced and established them in inland lakes and reservoirs such as Lake Nebagamon, Douglas County; Lake Owen, Bayfield County; and Gile Flowage, Iron County (WDNR, unpublished data). More detail on the distribution of smallmouth bass in Wisconsin can be found at https://cida.usgs.gov/wdnr_fishmap/map/.
Smallmouth bass prefer certain types of lakes. In Wisconsin and surrounding areas, they are most broadly distributed and abundant in cool or warmwater lakes and reservoirs with well-oxygenated, relatively clear water and areas of sandy or rocky bottoms (Cahn 1927; Becker 1983).
They occur in lakes as small as about 20 ha but are more frequently encountered in lakes over 80 ha and are common in the biggest lakes in the state, including Lake Winnebago, Lake Michigan, and Lake Superior (Becker 1983; Rahel 1986).
Smallmouth bass are absent in winterkill lakes, which have low dissolved oxygen concentrations under the ice in winter (<2 mg/l), and acidic lakes with pH below 5.6 (Rahel and Magnuson 1983; Rahel 1984). They also tend to be scarce in shallow (<9 m), boggy, or marshy lakes with clay or mud bottoms (Hubbs and Bailey 1938; Rahel 1984; Hinch et al. 1991).
Within lakes, smallmouth bass are generally most abundant in littoral areas with solid substrates such as sand, gravel, or cobble. In summer they are typically found in less than 9 m of water, but in some clear, well-oxygenated lakes, they may be found as deep as 25 m (Pearse 1921; Hubbs and Bailey 1938; Hile and Juday 1941). Smallmouth bass are often associated with gravel bars, underwater ledges, downed trees, or other types of “structure” (Cahn 1927; Coble 1975; Schneberger 1977; Wills et al. 2004; Brown and Bozek 2010), but they avoid areas of dense aquatic vegetation (Weaver et al. 1997).
Smallmouth bass also prefer certain types of rivers. They are found mainly in cool or warmwater streams and rivers of moderate to large size with moderate gradients and substantial rocky substrate (Lyons 1991).
They are most common in streams more than 8 m wide and have good populations in the largest rivers in the state, including the Wisconsin and Mississippi (Lyons et al. 2001).
In southwestern Wisconsin, streams as narrow as 4 m are nursery areas for young-of-year smallmouth bass, but adults are most abundant in streams more than 9 m wide (Forbes 1989). Generally, smallmouth bass prefer streams with maximum summer water temperatures that exceed 22.5°C (Lyons et al. 2009). Smallmouth bass occur most frequently in streams with gradients of 1–5 m/km and more than 45% rocky substrate (Lyons 1991). Rocky substrate is the best single predictor of smallmouth bass abundance; streams with less than 30% rock bottom typically have low densities, and maximum densities are in streams with 50–80%.
Within streams and rivers, smallmouth bass occupy specific habitats. They prefer gravel, cobble, or boulder areas but will also occupy sandy areas, particularly if logs or other cover objects are present (Rankin 1986; Sechnick et al. 1986; Todd and Rabeni 1989; Fore et al. 2007). They are most often found in pools and runs less than 1.5 m deep with some current, although they typically occupy a position behind a rock or log or in an eddy where minimal energy is needed to maintain position (Aadland 1993; Sabo et al. 1996; Remshardt and Fisher 2009).
The biology of smallmouth bass has been heavily studied for over 125 years, and excellent summaries of the state of knowledge at particular points in time are available in Henshall (1881), Hubbs and Bailey (1938), Scott and Crossman (1973), Stroud and Clepper (1975), Becker (1983), Jackson (1991) and Ridgway and Philipp (2002)
Smallmouth bass spawning has been examined in detail since the 1800s. In recent years, a series of excellent papers have been published that discuss various aspects of reproduction in Nebish Lake, Vilas County, and in Lake Opeongo, Ontario.
Smallmouth bass spawn in the spring. Males begin building a nest in bottom sediments when the daily average water temperature reaches about 13–15.5°C, which usually occurs from mid-May to early June in Wisconsin (Mraz 1960; 1964a; Forbes 1981; Gillooly et al. 2000). Spawning typically continues until average water temperatures reach 21°C, which is generally by mid-June to early July in Wisconsin (Pflieger 1966; Ridgway 1988; Baylis 1995), although spawning activities have been reported up to 26°C in the southern part of the species’ range (Wrenn 1984). Extended drops in average temperature below 13°C, substantial changes in water level (e.g., flooding in a stream, fluctuation in reservoir or river level from dam operation), or wave action from strong storms can cause males to abandon their nests, and fry to be killed (Cleary 1956; Latta 1963; Mraz 1964a; Wiegert 1966; Neves 1975; Shuter et al. 1980; Simonson and Swenson 1990; Swenson et al. 2002; Steinhart et al. 2005; Clark et al. 2008). If the temperature or water level change occurs early in the spawning period or spawning is unsuccessful for some other reason, males may re-nest later in June when conditions improve (Pflieger 1966; Lukas and Orth 1995). Male smallmouth bass usually nest in shallow protected areas over sand or gravel substrate. The nest is typically in 0.6–1.8 m of water but can be as shallow as 0.3 m in streams and as deep as 8 m in clear lakes (Hubbs and Bailey 1938; Mraz 1960; Latta 1963; Pflieger 1966; Neves 1975; Reynolds and O’Bara 1991). Nests are preferentially constructed near or under logs, boulders, or other types of cover, but males will nest in open areas if no cover is available (Hubbs and Bailey 1938; Mraz 1964a; Forbes 1981; Hoff 1991; Bozek et al. 2002; Saunders et al. 2002). In lakes, most nests are constructed along the warmest, most complex shorelines (i.e., convoluted, with many small bays and points) where wave action is limited (Rejwan et al. 1999). In streams and rivers, nests are usually in the quiet water of the edge of pools and side channels (Pflieger 1966, 1975; Reynolds and O’Bara 1991). The nests are saucer-shaped, cleared areas of the bottom that range from 0.4 to 0.8 m in diameter (Mraz 1964a; Pflieger 1966; Neves 1975; Saunders et al. 2002).
The male builds the nest by sweeping away fine sediment and detritus with his tail. Nest construction takes from 4 to 48 hours, and the male may build several nests before finally settling on one for the remainder of spawning (Cleary 1956; Mraz 1964a). Nest densities in good habitat can exceed 30/km in streams and rivers (Pflieger 1966) and 60–125/km in lakes (Rejwan et al. 1997; Gillooly et al. 2000). Males guard the nest and attempt to attract females for spawning. Courtship and spawning behaviors are described in detail by Reighard (1906) and Ridgway et al. (1989) Individual females produce 2,000–23,000 eggs per year (Schneberger 1977; Serns 1984a), and the number of eggs per nest ranges from about 500 to 16,000 (Pflieger 1966; Neves 1975; Wiegmann et al. 1992). In Nebish Lake, smallmouth bass are generally monogamous within a spawning season; a single male spawns only with a single female and vice versa (Wiegmann et al. 1992). However, there are reports from other waters of a single male spawning with two females simultaneously and of a single female depositing eggs in a second nest after her spawning at the first nest was disrupted (Reighard 1906; Neves 1975). In Nebish Lake, males spawned only once in their lifetime (Baylis et al. 1993; Baylis 1995), but in Lake Opeongo many males spawned at least two times (Ridgway et al. 1991). Lake Opeongo males tended to spawn in the same area each time; 21% returned to the same nesting spot the second year they spawned, and 81% nested within 200 m of their original nest the second year.
Many potential smallmouth bass spawners do not actually spawn in a given year, and of those that do, a small proportion produces most of the offspring. In Nebish Lake, the number of nests as a percentage of potential spawners was less than 10% in some years (Raffetto et al. 1990; Wiegmann et al. 1992; Gillooly et al. 2000). Further, many of the males that nested did not acquire a mate. In a bay in Lake Opeongo, only 28% of those males that mated actually produced offspring that survived into the fall, and 5.4% of the spawning males (N = 11) produced 54.7% of the young-of-year smallmouth bass present in the fall (Gross and Kapuscinski 1997). In a Virginia river, six males accounted for 31% of the young of year produced over a 4.8 km stretch (Lukas and Orth 1995).
Several studies have attempted to identify which characteristics of a guarding male result in successful production of young. Males guard the eggs and larvae while they are in the nest and after they swim up out of the substrate, and they may continue to guard the fry for 7–10 days after they disperse from the nest (Forbes 1981; Scott et al. 1997). The spawning period for individual males ranges from about 10 to 40 days and is energetically very costly (Hinch and Collins 1991; Gillooly and Baylis 1999; Mackereth et al. 1999; Gravel et al. 2010). However, protection by the male is critical for the successful production of young. Larger and more aggressive males are better guardians and are more likely to produce a successful nest, although the situation is complex, and nest location and weather conditions are also critical to nest success (Wiegmann and Baylis 1995; Gross and Kapuscinski 1997; Wiegmann et al. 1997; Rejwan et al. 1999; Bozek et al. 2002; Saunders et al. 2002; Wills et al. 2004; Kaevats et al. 2005; Steinhart et al. 2005). When males are removed from the nest by anglers, even for only a few minutes during catch-and-release angling, there may be substantial predation on the fry, and subsequent nest abandonment and failure often results (Philipp et al. 1997; Ridgway and Shuter 1997; Hanson et al. 2008). Whether nest failures caused by low to moderate amounts of angling will result in reduced recruitment to the adult population is unclear (Steinhart et al. 2005).
In Nebish Lake, there is an interesting pattern of alternating growth and age at reproduction for successive generations (Raffetto et al. 1990; Wiegmann et al. 1992; Baylis et al. 1993; Baylis 1995; Wiegmann and Baylis 1995; Wiegmann et al. 1997). The fastest growing smallmouth bass males nest at age 3, and slower growing fish nest at age 4 or 5. However, the older nesters are larger and are able to spawn earlier in the season, giving them a longer growing season, and as a result their offspring are larger in the fall than those of age-3 spawners. These larger offspring continue to grow faster throughout their lives and ultimately become age-3 spawners, whereas offspring of age-3 spawners grow more slowly and ultimately become age-4 and -5 spawners, and the cycle repeats. This pattern is stable despite wide annual fluctuations in the number of spawning adults and nests. The number of eggs produced in Nebish Lake is negatively related to the biomass of the spawning population but unrelated to the number of young smallmouth bass produced (Gillooly et al. 2000).
Climatic factors appear to be particularly important in determining smallmouth bass reproductive success. In northern lakes, including Nebish Lake, relatively warm temperatures in the first summer of life tend to result in better survival of juvenile smallmouth bass and ultimately greater recruitment to adulthood (Clady 1975; Shuter et al. 1980; Serns 1982). In larger lakes, years with high winds and large waves from strong storms during the spawning period resulted in reduced reproductive success (Steinhart et al. 2005). In northern streams and rivers, floods during and immediately after spawning limit reproduction, and the best smallmouth bass year classes are often produced in drought years when flows are low and water temperatures are relatively warm (Cleary 1956; Mason et al. 1991; Peterson and Kwak 1999; Swenson et al. 2002). However, in streams at the southern edge of the smallmouth bass range in Arkansas and Oklahoma, drought may lead to substantial reductions in suitable habitat, poor reproductive success, and reduced juvenile survival (Remshardt and Fisher 2009; Hafs et al. 2010).
Smallmouth bass eggs are 0.9–2.8 mm in diameter, with an average of about 2.0–2.2 mm (Fish 1932; Hubbs and Bailey 1938; Meyer 1970). Hatching takes 10–15 days at water temperatures below 13°C, 6 days at 15.5°C, 5 days at 19°C, 4 days at 21°C, and 2 days or less above 23°C (Fish 1932; Mraz 1964b; Tin 1982). At hatching, the larvae are 4.6–5.0 mm TL. Newly hatched larvae remain largely motionless on the bottom of the nest for 6–15 days, depending on the temperature, before their yolk sac is absorbed and they become free-swimming and feeding “black fry” at about 9 mm TL (Hubbs and Bailey 1938; Meyer 1970; Tin 1982; Becker 1983). At about 11 mm TL the fins are formed, and by 19 mm TL, 5–7 days after swim-up, the black color has faded to brownish or bronze, scales become evident, and the fish begin to disperse from the nest (Reighard 1906; Scott and Crossman 1973; Tin 1982). At 38–51 mm TL the smallmouth bass has essentially achieved its adult morphology. Developmental stages for smallmouth bass eggs and larvae are described and figured in Reighard (1906), Fish (1932), Hubbs and Bailey (1938), Doan (1939), Meyer (1970), Tin (1982) and Holland-Bartels et al. (1990)
Although they are considered a mobile predator, most smallmouth bass populations that have been studied are not highly migratory (Hubbs and Bailey 1938; Latta 1963; Coble 1975; Ridgway and Shuter 1996; Savitz and Treat 2007). In many systems, smallmouth bass are thought to spend most of their lives within 8 km of where they were hatched. Fish displaced out of their home area tend to return to that home area (Ridgway and Shuter 1996; Gunderson VanArnum et al. 2004).
Some smallmouth bass populations, however, do undertake seasonal migrations greater than 8 km, especially to reach spawning habitats in the spring but also in some cases to reach over-wintering habitats in the fall (Lyons and Kanehl 2002). Migrations from large lakes or rivers into tributaries for spawning is fairly common (e.g., out of Green Bay), although typically only part of the population migrates to the tributaries and the remainder spawns in the lake or river (e.g., Robbins and MacCrimmon 1977; Forbes 1989; Humston et al. 2010). Migratory fish usually return to the lake or river soon after spawning is complete.
Some riverine populations have more complex migratory behavior related to both spawning and over-wintering habitat (Lyons and Kanehl 2002). Migration distance appears to be positively related to winter severity. The longest reported migrations occur in the Embarrass and Wolf rivers in northeastern Wisconsin, where winters are relatively harsh (Langhurst and Schoenike 1990). Here, adult smallmouth bass leave the Embarrass River in the fall and enter the Wolf River for the winter. The average distance traveled is 77 km, and some individuals travel as far as 109 km. In the spring, these smallmouth bass return to the Embarrass River to spawn and spend the summer, many to within 8 km of where they had been the previous summer. In the Otter Creek–Pecatonica River system in southwestern Wisconsin, where the winters are not as long or cold, adult smallmouth bass also migrate to winter habitats in the fall, but the distance traveled averages only 6.3 km with a maximum of 21 km (Lyons and Kanehl 2002). In the spring, these fish migrate approximately the same distances back to spawning and summer habitats that are within 8 km of where they had been the previous summer. In rivers in Michigan, Illinois, Missouri, and Idaho, where winter conditions are more benign, seasonal movements are much shorter, averaging only 0.2–0.3 km.
Winter activity and habitat use by smallmouth bass are poorly known. Early anecdotal accounts, summarized in Hubbs and Bailey (1938) indicated that in winter smallmouth bass “become inactive, take practically no food, and seek seclusion.” In areas with harsh winters, there are accounts of smallmouth bass found burrowed into hollow logs or wedged into crevices between rocks. Smallmouth bass were also found in deeper, slower water than they typically occupy during the summer. However, recent studies of river populations suggest that winter habitat use and activity vary more among populations than previously believed, with little relation to winter severity (Lyons and Kanehl 2002). In some populations fish moved to the deepest water near cover and became almost quiescent, whereas in other populations they stayed in open water, and remained active, not occupying the deepest areas. For example, in the winter in the Pecatonica River, smallmouth bass were found in 0.9–1.8 m of water with little cover despite the presence of pools up to 3 m deep, and they moved upstream and downstream within river stretches 0.13–0.71 km long.
The smallmouth bass has been variously classified as a coolwater or a warmwater species, and there is some disagreement in the scientific literature about its preferred water temperature (Lyons et al. 2009). Field observations in northern Wisconsin and Ontario lakes reveal that smallmouth bass prefer water 21–26°C even when warmer water is available (Hile and Juday 1941; Scott and Crossman 1973). Nonetheless, smallmouth bass also thrive in warmer waters, such as the Lower Wisconsin River where maximum summer temperatures regularly exceed 26°C. Laboratory experiments indicate an ability to tolerate temperatures of up to 33°C for extended periods and over 35°C for short periods (Wrenn 1980; Smale and Rabeni 1995). Bevelheimer (1996) found that availability of shelter and food was more important than temperature in determining smallmouth bass distribution in laboratory tanks. Field observations over their U.S. range show that smallmouth bass rarely occur in waters where the maximum weekly mean temperature is more than 29.5°C (Eaton and Scheller 1996). Missouri smallmouth bass had high metabolic costs and lost weight even at unlimited food availability when average water temperatures exceeded 27°C (Whitledge et al. 2003, 2006). However, waters with average temperatures above 27°C are currently rare in Wisconsin (Lyons et al. 2009), and recent computer simulation modeling of potential climate change effects indicates that smallmouth bass are likely to substantially increase their distribution in Wisconsin streams and rivers over the next 50–100 years under the most likely climate warming scenarios (Lyons et al. 2010).
Smallmouth bass densities and standing crops vary substantially over time and among waters in Wisconsin. From 1972 to 1992, springtime densities of adult smallmouth bass (age 3 and older) in Nebish Lake varied from 11.1 to 96.7 fish/ha, and biomass varied from 1.8 to 11.6 kg/ha (Engel et al. 1999). In nearby Pallette Lake, Vilas County, springtime densities of adult fish ranged from 1.5 to 9.9 fish/ha during 1963–1979 (Hoff and Serns 1990). Densities fluctuated from 1.4 to 16.8 fish/ha for age–2 fish and from 4.9 to 30.3 fish/ha for age-1 fish. Adult abundance estimates for five other northern Wisconsin lakes during the 1970s varied from 0.7 to 8.6 fish/ha and 0.1 to 1.3 kg/ha (WDNR, unpublished data). Maximum densities were higher in flowing water, and summer values for age 1 and older smallmouth bass from 21 streams and rivers throughout Wisconsin from 1964 to 1990 ranged from 0.7 to 395.4 fish/ha (Forbes 1985; Lyons and Kanehl 1993). Biomass in eight streams varied from 1.0 to 31.6 kg/ha (Paragamian and Coble 1975; Forbes 1985, 1989). However, Lyons and Kanehl (1993) presented evidence than many of the stream estimates were likely biased too high.
Mortality of smallmouth bass is often substantial. Annual mortality rates in Wisconsin ranged from 32% to 91% for adults (Paragamian and Coble 1975; Marinac-Sanders and Coble 1981; Forbes 1989; Hoff and Serns 1990; Engel et al. 1999). Mortality rates were positively correlated with fishing harvest, and harvest often accounted for as much as 90% of observed mortality (Engel et al. 1999). Larval and small juvenile smallmouth bass, although not subject to significant angling harvest, had even lower annual survival. Serns (1984a) compared the potential number of eggs that could be produced by all the smallmouth bass females in Nebish Lake with the number of young-of-year fish present in the fall and estimated that survival was only 0.1–0.5%. However, because many of the mature smallmouth bass females in Nebish Lake did not lay eggs in a particular year (Raffeto et al. 1990), the survival rate for eggs that were actually spawned was higher.
Annual production of smallmouth bass has been estimated only a few times for Wisconsin and adjacent areas. In infertile Nebish Lake, production of age–3 and age–4 fish combined ranged from 0.7 to 4.8 kg/ha during 1974–1981 (Serns 1984b). Ratios of production to biomass were 0.41–0.98. In Katherine Lake, an infertile lake in the Upper Peninsula of Michigan just north of the Wisconsin border, production of smallmouth bass age 3 and younger was 4.7–5.6 kg/ha during 1967–1969, and production to biomass ratios averaged 1.1 (Clady 1977). In the fertile Maquoketa River in northeastern Iowa, production of smallmouth bass age 1–5 was 6.4–15.0 kg/ha, and production-to-biomass ratio averaged 0.34 (Paragamian 1987). In fertile Bear Creek, southeastern Minnesota, production of all ages of smallmouth bass during 1985–1988 was 24.1–43.8 kg/ha, and production-to-biomass ratios averaged 1.25 (Waters et al. 1993).
The smallmouth bass is a top carnivore, and feeding studies from Wisconsin and adjacent areas reveal a wide variety of animal prey (Pearse 1915, 1918, 1921; Cahn 1927; Couey 1935; Coble 1975; Becker 1983; Serns and Hoff 1984; Rabeni 1992; Waters et al. 1993; Pert et al. 2002). Small juveniles eat mainly crustaceans, especially cladoceran zooplankton and amphipods, and aquatic insects, especially dipterans, ephemeropterans, hemipterans, and odanates. Larger smallmouth bass eat mainly crayfish, small fish, and, in some cases, aquatic insects. Cannibalism occurs but typically is not major. Based on laboratory experiments and analyses of stomach samples from the Plover River, Portage County, Paragamian (1976) found that smallmouth bass were more likely to eat common shiners than hornyhead chubs or white suckers.
Smallmouth bass feeding varies over time. They are daytime predators, with feeding peaks at dawn and dusk (crepuscular) and little activity at night (Emery 1973; Helfman 1981; Kwak et al. 1992). They eat little or nothing in winter, living instead off fat reserves, and feeding generally ceases at water temperatures below 10°C (Hubbs and Bailey 1938; Shuter and Post 1990).
Smallmouth bass are found in diverse fish assemblages, and they occur with a wide variety of other fish species. In southwestern Wisconsin streams, smallmouth bass were most frequently found with stonecat and rosyface shiner (= carmine shiner) (Lyons et al. 1988). Common shiner, hornyhead chub, sand shiner, white sucker, and golden redhorse were other common associates. The stonecat and smallmouth bass also co-occur frequently in Ohio (Trautman 1981) and Michigan streams (Zorn et al. 2002) but not elsewhere (Lyons et al. 1988). In statewide multivariate analyses of Wisconsin stream data, smallmouth bass had similar distribution patterns with 17 other species, including common shiner, rosyface shiner (= carmine shiner), hornyhead chub, white sucker, and rock bass, but not stonecat, sand shiner, or golden redhorse (Lyons 1989, 1996). The rock bass has long been identified as a common associate of the smallmouth bass in rivers and lakes (Carlander 1975; Lyons et al. 1988).
As a top carnivore, the smallmouth bass has a major effect on aquatic communities, both directly through predation and competition and indirectly through modification of the distribution and behavior of its primary prey, crayfish and small fish (Roell and Orth 1994). In northern Wisconsin lakes and elsewhere, smallmouth bass predation accounts for a substantial fraction of crayfish mortality, and the threat of smallmouth bass predation limits small crayfish to certain types of habitats with hiding cover, such as cobble substrates (Stein and Magnuson 1975; Stein 1977; Rabeni 1992; Kershner and Lodge 1995; Magoulick 2004). Crayfish are major consumers of snails, macrophytes, and detritus, so smallmouth bass effects on crayfish abundance and distribution in turn influence other trophic levels (Stein and Magnuson 1975; Olsen et al. 1991). Selective predation by smallmouth bass on smaller and less aggressive native crayfish species has helped the larger and more aggressive exotic rusty crayfish, Orconectes rusticus, to replace the native crayfish in northern Wisconsin lakes and Ohio and New York streams (DiDonato and Lodge 1993; Mather and Stein 1993; Roth and Kitchell 2005; Kuhlmann et al. 2007.). However, smallmouth bass predation helped limit the abundance of rusty crayfish in Sparking Lake, Vilas County, where the species was already established (Hein et al. 2006, 2007).
Smallmouth bass predation can also influence the abundance and distribution of other fish species. In laboratory experiments, the threat of smallmouth bass predation restricted activity by johnny darters and limited them to areas of cover (Rahel and Stein 1988). In an experimental stream in Minnesota, the threat of smallmouth bass predation forced hornyhead chub to use shallow pool margins even though they preferred deeper structurally complex pool habitats in the absence of smallmouth bass (Schlosser 1988). Similarly, in an Arkansas stream, the presence of adult smallmouth bass led to lower densities of small minnows and darters and caused them to make greater use of shallow habitats than they would have otherwise (Magoulick 2004). When small prey fishes are forced to use shallow habitats, they may become more vulnerable to predation by herons and other fish-eating wading birds (Steinmetz et al. 2008). In an Oklahoma stream, predation by juvenile smallmouth bass was associated with reduced densities of larval fish (Harvey 1991). However, the presence of adult smallmouth bass reduced the density and foraging activity of juvenile smallmouth bass and was associated with increased densities of larval fish. In contrast to these findings, threats of smallmouth bass predation had relatively little influence on the distribution of central stonerollers in some Oklahoma and Arkansas streams (Matthews et al. 1987; Harvey et al. 1988). Predation by introduced smallmouth bass is implicated in decreases in trout and salmon populations in the northwestern and northeastern United States (Fletcher 1991; Tabor et al. 1993; Fritts and Pearsons 2004, 2006; Weidel et al. 2007) and minnow extirpations from lakes in central Ontario and the northeastern United States (Whittier et al. 1997; Findlay et al. 2000; MacRae and Jackson 2001; Albright et al. 2004; Vander Zanden et al. 2004; Weidel et al. 2007). Competition from introduced smallmouth bass is blamed for declines in lake trout populations in Ontario and New York lakes (Vander Zanden et al. 1999, 2004; Lepak et al. 2006) and walleye abundance and growth in northern Minnesota lakes (Johnson and Hale 1977) and South Dakota reservoirs (Wuellner et al. 2010). Interestingly, walleye introductions have been associated with declines in smallmouth bass populations in northern Wisconsin lakes, best documented in Escanaba Lake, Vilas County, so the walleye-smallmouth bass interaction is complex (Kempinger et al. 1975; Colby et al. 1987). In Big Pine Lake, Iron and Price counties, angler catches of smallmouth and largemouth bass over a 70-year period were negatively correlated with that of walleye, and high bass catches were associated with a decade of warmer-than-average summer temperatures (Inskip and Magnuson 1983).
The smallmouth bass is relatively sensitive to certain types of environmental degradation, particularly sedimentation and organic pollution, and its abundance is a useful indicator of river and lake quality in Wisconsin (Lyons et al. 1988; Mason et al. 1991; Jennings et al. 1999). The smallmouth bass is considered an intolerant species in Wisconsin versions of the index of biotic integrity, a procedure for assessing the health of aquatic ecosystems based on their fish communities (Lyons 1992; Lyons et al. 2001).
The smallmouth bass is one of the most popular game fishes among anglers in Wisconsin and elsewhere in temperate North America. It is often referred to as “inch for inch and pound for pound the gamest fish that swims” (Henshall 1881). Aficionados of other sport fishes may dispute this assertion, but the smallmouth bass is without question a strong fighter and a worthy quarry for any angler. It is also an excellent table fish, delicious when baked, broiled, grilled, or fried.
Smallmouth bass fishing is a major recreational activity across Wisconsin and much of the United States and Canada. In a U.S. national survey, black bass (Micropterus species) was the most popular freshwater game fish group, with over 13 million anglers and 196 million angling days per year (USDI, FWS and USDOC, BOC 1996). In Wisconsin during the 2006–2007 fishing season, the smallmouth bass was the sixth-most sought-after and captured sport fish species (bluegill first, largemouth bass fifth), with an estimated annual catch of over 4.6 million (Brian Weigel, WDNR, personal communication, 2008). At least 500 Wisconsin lakes and reservoirs (WDNR 1991) and 5,670 km of streams and rivers (WDNR 1978) have fishable smallmouth bass populations. Some of these waters, such as Lake Geneva (Walworth County), Lake Owen (Bayfield County), Green Bay, Lake Michigan (Door County), Chequamegon Bay, Lake Superior (Ashland and Bayfield counties), the Galena (Fever) River (Lafayette County), the Wisconsin River (Grant through Vilas counties), and the St. Croix River (Pierce through Douglas counties), support famous smallmouth bass fisheries. Angler catch rates on the best waters average from 0.2 to over 1 smallmouth bass per hour (Rasmussen et al. 1994; Engel et al. 1999; Newman and Hoff 2000; WDNR, unpublished data).
Fisheries management of smallmouth bass in Wisconsin has a long and varied history. Initially, beginning in the late 1800s and peaking in the 1920s through 1970s, stocking was emphasized. Although never as widely cultured as walleye, muskellunge, trout, or salmon, many millions of smallmouth bass and “black bass” (largemouth and smallmouth bass combined) fry and fingerlings were raised and stocked in Wisconsin (e.g., U.S. Bureau of Fisheries 1909; Cahn 1927; Robbins and MacCrimmon 1974; Lathrop et al. 1992). Much of this stocking was in waters that already had smallmouth bass, but some occurred where the species was absent. There were no evaluations of the effects of this stocking, but smallmouth bass did become established in some waters where they historically did not occur, such as inland lakes of the Lake Superior basin (Robbins and MacCrimmon 1974).
Stocking of smallmouth bass dropped off after the 1970s. The species is relatively expensive to culture, as either specialized intensive techniques or extensive pond areas are needed to raise large numbers of smallmouth bass eggs and fry (Flickinger et al. 1975; Inslee 1975; Snow 1975). The great demand for walleye and muskellunge leaves few hatchery resources for raising smallmouth bass, and the current perception among WDNR fish managers is that little smallmouth bass stocking is needed. At present, an average of 50,000 to 75,000 50–mm TL smallmouth bass fingerlings are produced and stocked in Wisconsin per year (Al Kaas, WDNR, personal communication, 2010). Fields et al. (1997) provided guidelines to minimize effects of stocking on smallmouth bass genetic diversity in the state.
From the 1940s through the 1970s, lake “rehabilitation,” the elimination of a lake’s fish population through poisoning followed by restocking with selected game and forage fish species, was a common fisheries management practice in Wisconsin (Klingbiel 1975). However, few of these rehabilitation projects focused on smallmouth bass (Christenson et al. 1982). One notable exception was Nebish Lake. Originally, smallmouth bass were abundant in Nebish Lake (Hile and Juday 1941), but by 1966, when the lake was poisoned, introductions of other species had reduced smallmouth bass to only 3% of the total fish standing crop (Kempinger and Christenson 1978). Smallmouth bass angler harvest rate for the 11 years prior to 1966 averaged 0.12 fish/hr and yielded about 0.9 kg/ha (Christenson et al. 1982). Smallmouth bass were removed from the lake before the poisoning and then restocked afterwards. By the early 1970s, the smallmouth bass standing crop was about 2.5 times higher than before the poisoning (Kempinger et al. 1982). Angling pressure had jumped by 170%, and angler harvest rates had increased by nearly 200% and yield by almost 500% (Christenson et al. 1982). The smallmouth bass population and fishery has remained good up to the present (Engel et al. 1999). However, despite this success, future lake rehabilitation projects focused primarily on improving smallmouth bass fishing are unlikely because of high costs and ethical concerns (Becker 1975, 1983; Bettoli and Maceina 1996; WDNR, unpublished data).
Angling regulations have been a key component of smallmouth bass management in Wisconsin. The first restrictions on harvest, closing the fishing season from December through February, were enacted in 1881 (WDNR, unpublished data). The first daily bag limit–15 largemouth and smallmouth bass combined–was established in 1907. A 254–mm (10–inch) TL minimum size limit took effect in 1917. The size limit was removed in 1953, part of a nationwide trend at the time to liberalize sport fishing regulations, the general feeling being that angling was unlikely to harm a fish population when habitat conditions were good (e.g., Churchill 1957; Mraz 1964b; Kempinger et al. 1975). However, it became clear in the 1970s and 1980s that excessive angling harvest could reduce the quality of sport fish populations. Greater fishing effort, spurred by human population growth and coupled with greater fishing effectiveness, the result of improved technology, made stricter angling regulations necessary. Population modeling and evaluation of minimum size limits in Clear Lake, Oneida County (Marinac-Sanders and Coble 1981); Nebish Lake (Kempinger et al. 1982; Serns 1984b; Hoff 1995); and several rivers outside Wisconsin (reviewed in Paragamian 1984a, 1984b; Lyons et al. 1996), demonstrated that smallmouth bass survival, abundance, and biomass could be improved with appropriate restrictions on angler harvest. Consequently, in 1989, minimum length limits for harvest of smallmouth bass were again imposed in Wisconsin. This regulation change corresponded with a shift in management philosophy towards reduced smallmouth bass harvest through “catch and release”, emphasizing the species’ value as a sport fish rather than a panfish. Presently, there is a statewide 356-mm (14-inch) TL minimum size limit and a bag limit of five largemouth and smallmouth bass combined. This size limit has improved smallmouth bass abundance and size structure in many waters around the state (Lyons et al. 1996; WDNR, unpublished data).
“Experimental” angling regulations have been implemented on a few smallmouth bass waters. At a few localities, protected “slot” size limits are in effect; fish can be harvested above and below but not from within the slot. In Nebish Lake, a 229–305 mm (9–12 inch) TL slot limit improved the density of spawning-size smallmouth bass (Engel et al. 1999). At other localities, higher minimum size limits and more restrictive bag limits are in place. In Pallette Lake, a 406–mm (16–inch) TL minimum and two-fish bag limit significantly increased smallmouth bass abundance and average size (Newman and Hoff 2000). In Chequamegon Bay, Lake Superior, near Ashland, a 559-mm (22-inch) minimum and one-fish bag also significantly increased smallmouth bass abundance and size (Mike Seider, WDNR, personal communication, 2008).
Degradation of water and habitat quality limits smallmouth bass populations and fisheries in a number of Wisconsin waters, and management efforts have focused on environmental restoration at these sites. For many years, discharges of inadequately treated municipal sewage, pulp and paper mill wastes, and other industrial pollutants severely degraded water quality in many Wisconsin rivers. In rivers such as the Wisconsin and Fox (Green Bay), only small remnant populations of smallmouth bass (and most other fish species) were able to persist (e.g., Coble 1982). Over the last 30 years a massive investment in reduction and treatment of this “point-source” pollution has led to greatly improved water quality in most Wisconsin rivers (WDNR 2000). As a result, smallmouth bass populations have rebounded and now support fisheries (Rost 1989; Lyons et al. 2001).
As point-source pollution impacts on smallmouth bass have been reduced in Wisconsin, the effects of more diffuse “nonpoint-source” pollution from agriculture and urbanization have become more apparent. Erosion from poor land use has led to sedimentation of rocky substrate and loss of smallmouth bass habitat in some southwestern Wisconsin streams (Lyons et al. 1988) and more generally in agricultural regions throughout the Midwest (Paragamian 1991; Waters 1995). Runoff of manure and fertilizer from farms during rain storms into several southwestern Wisconsin streams has caused short-term (<6 hours) but severe drops in dissolved oxygen (to <1 mg/l), resulting in fish kills that have devastated smallmouth bass populations (Forbes 1985, 1989; Mason et al. 1991; Graczyk 1993; WDNR, unpublished data). Efforts to reduce erosion and runoff into streams and lakes in agricultural areas have been a major management focus for the WDNR over the last 30 years (e.g., Konrad et al. 1985). However, the huge spatial scope and the pervasive, diffuse nature of the nonpoint-source pollution problem in Wisconsin, coupled with a lack of regulation of many land-use activities, have limited the extent and magnitude of stream and lake restoration (Wolf 1995; WDNR, unpublished data). Direct improvement of smallmouth bass habitats degraded by sedimentation has been recommended for Wisconsin streams (Lyons and Courtney 1990), but thus far the only habitat improvement projects that have been documented to benefit smallmouth bass have been associated with dam removals.
Dam removal has become an increasingly common strategy to restore riverine environments in Wisconsin. Dams, thousands of which occur in Wisconsin (Becker 1983), affect many smallmouth bass populations by blocking essential seasonal movements and forming impoundments that inundate flowing-water habitats (Kanehl et al. 1997; Lyons and Kanehl 2002). Pajak (1992) estimated that smallmouth bass habitat would be increased by 18% if low-head dams were removed from the Milwaukee River in southeastern Wisconsin. Dam removal was a more cost-effective management strategy than watershed erosion control or instream habitat improvement. After the Woolen Mills Dam was removed from the Milwaukee River at West Bend, Washington County, in 1988, smallmouth bass abundance and biomass increased dramatically (Kanehl et al. 1997). The increases were caused by improved reproduction and recruitment, the result of unrestricted access to spawning areas above the dam, and improved habitat in the former impoundment. Much of the improvement in habitat occurred through natural river channel recovery, but addition of habitat improvement structures within parts of the former impoundment further enhanced habitat quality and led to greater smallmouth bass population increases.
In Wisconsin lakes, shoreline development for residential or recreational use has eliminated much of the large woody debris in the littoral zone (Christensen et al. 1996; Jennings et al. 1999). This debris is a favored nesting area for smallmouth bass (Hubbs and Bailey 1938; Mraz 1964a; Forbes 1981; Bozek et al. 2002; Saunders et al. 2002). Additions of “half-log” structures for nesting cover significantly increased the number of successful smallmouth bass nests and production of smallmouth bass juveniles in three northern Wisconsin lakes (Hoff 1991) and in Michigan reservoirs (Wills et al. 2004).