Compared to other parts of the United States, many fish species live in the Ozark Plateaus. Approximately 175 species (including introduced species) are present in the Ozark Plateaus province part of the Study Unit; at least 16 of these species exist nowhere else in the world. Many of these 175 species are intolerant of habitat or water-chemistry degradation.
Fish communities are a useful tool in assessing water-chemistry and habitat conditions of streams. Many fish species are sensitive to a wide array of stresses that are integrated over their lifetimes, are relatively widely distributed, and are relatively easy to identify.
In streams in agricultural basins, algae-grazing stonerollers generally are the most abundant type of fish. Generally, 20 to 50 percent of the fish are stonerollers.
In streams in forested basins, minnows (other than stonerollers), sunfish, and darters are a larger percentage of the fish community than in agricultural basins. Generally, 10 to 20 percent of the fish are stonerollers.
A major difference between the composition of fish communities at sites in forested basins and agricultural basins is the difference in the relative abundance (percentage of total individuals in the community) of two types of minnows called "stonerollers" that are among the most abundant fish species in Ozark streams. Stonerollers graze on algae attached to rocks and other submerged surfaces. Streams in agricultural basins typically have high concentrations of nutrients and less riparian shading (which allows more sunlight to reach the streambed), promoting algal growth. Greater amounts of this food source encourage greater numbers of stonerollers. The median relative abundance of stonerollers at forested sites (in 1995) was 14 percent; the median abundance at agricultural sites was 35 percent. Whether this greater abundance can have detrimental effects on the aquatic community is unknown, although apparently stonerollers selectively graze on different types of algae and affect the density and composition of benthic invertebrates (Gelwick and Matthews, 1992).
The increased abundance of stonerollers is an indication of increased nutrients in Ozark streams. Other factors (including toxicity and changes in channel shape) can also affect stoneroller abundance. The relative abundance (17 percent) of stonerollers at a site on Center Creek, downstream from a lead-zinc mining area and from industrial and municipal wastewater-treatment plant discharges near Joplin, Mo., may be lowered because of toxicity. The abundance (46 percent) of stonerollers at a site on the Kings River, downstream from a small wastewater-treatment plant and instream gravel mining, may be elevated because of nutrient enrichment and other habitat changes.
Stonerollers are very common in the Ozarks. They generally are more abundant in streams in agricultural basins.
Stonerollers are more abundant (relative to other species) at sites in agricultural basins, and sunfish (including the black basses-smallmouth, largemouth, and spotted bass) are less abundant at these sites. Many of the sunfish species in the Ozarks are sensitive to degraded water chemistry or habitat. Much of this decrease in relative abundance (percentage of total individuals) is because of the greater relative abundance of stonerollers; but even after discounting the stoneroller data, sunfish generally have lower relative abundance values at agricultural sites than at forested sites. The median relative abundance of sunfish at forested sites was 11 percent (26 percent of individuals other than stonerollers); whereas, the median relative abundance at agricultural sites was 4 percent (6 percent of other than stonerollers). Members of the sunfish family, especially smallmouth bass, are important game fish in Ozark streams. Spotted bass, largemouth bass, longear sunfish, Ozark bass, shadow bass, and rock bass are less important, either because of fewer numbers or smaller size.
Smallmouth bass, an important game fish, are sensitive to degraded habitat or water chemistry. (Photograph courtesy of Gregg Patterson.)
Darters also comprise a smaller percentage of the communities at sites in agricultural basins. As with sunfish, much of this is because of the greater relative abundance of stonerollers; but after discounting the stoneroller data, darters generally remain relatively less abundant at sites in agricultural basins. The median relative abundance of darters at forested sites was 14 percent (18 percent of other than stonerollers). The median relative abundance at agricultural sites was 4 percent (8 percent of other than stonerollers). Darters generally are considered to be sensitive to water-chemistry or habitat degradation. At least seven species of darters in the Ozarks (Arkansas saddled darter, yoke darter, yellowcheek darter, stippled darter, bluestripe darter, Missouri saddled darter, and Niangua darter) exist nowhere else in the world. The Niangua darter, which is found in only a few tributaries of the Osage River in central Missouri, is a federally listed threatened species under the Endangered Species Act.
Darters also are sensitive to degraded habitat or water chemistry. This Niangua darter is one of seven species of darter found only in the Ozarks. (Photograph courtesy of Missouri Department of Conservation.)
Results of several statistical procedures (multivariate analyses, correlation, and regression) used to group and compare the fish communities at 18 sites in the Study Unit indicate that these communities are substantially affected by their habitat. However, the procedures used to group sites often do not completely separate sites in agricultural areas from those in forested areas. This indicates that factors related to land use are important in determining community structure, but that other factors also are important.
Several measures of stream size appear related to community composition. These measures include stream width and depth, width-to-depth ratio, and stream order. This result is reasonable, considering that several species of fish have preferences for smaller, steeper gradient, lower order streams, while others have preferences for larger, lower gradient, higher order streams. Several other factors that can be affected by stream size and land use also appeared to be related to community structure at the 18 sites. These factors were canopy angle, substrate size, sinuosity, and velocity.
Several water-chemistry factors appeared to be related to the fish community composition. Phosphorus, sediment, and nitrate concentrations were related to the community composition in results from at least one of the multivariate procedures.
Many of these factors probably affect spawning success and food availability. Smallmouth bass, some other sunfish, many minnows, and most darters are intolerant of turbidity or siltation. Stonerollers are favored by increased algal growth, which results from elevated nutrient concentrations and large (open) canopy angles.
The site on Center Creek (map, p. 19) has one of the highest percentages in the study area of individuals tolerant of degraded water chemistry or habitat. The site also has a relatively low percentage of stonerollers for a site with elevated nutrient concentrations and an open canopy. This site, which is downstream from lead-zinc mining and urban areas, has elevated concentrations of lead, zinc (table, p. 12), and semivolatile organic compounds (p. 11) in bed sediment. These chemicals may be a major factor affecting the Center Creek fish community.
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Petersen, J.C., Adamski, J.C., Bell, Davis, J.V., Femmer, S.R., Freiwald, D.A., and Joseph, R.L., 1998, U.S. Geological Survey Circular 1158, on line at < URL: http://water.usgs.gov/pubs/circ1158>, updated April 3, 1998
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