Fish Communities of Benchmark Streams in Agricultural Areas of Eastern Wisconsin

USGS Water-Resources Investigation Report 96-4038-D

Fish Communities of Benchmark Streams in Agricultural Areas of Eastern Wisconsin

By Daniel J. Sullivan and Elise M. Peterson

Abstract

Fish communities were surveyed at 20 stream sites in agricultural areas in eastern Wis consin in 1993 and 1995 as part of the National Water-Quality Assessment (NAWQA) Program. These streams, designated "benchmark streams," were selected for study because of their potential use as regional references for healthy streams in agricultural areas, based on aquatic communities, habitat, and water chemistry. The agricultural benchmark streams were selected from four phys ical settings, or relatively homogeneous units (RHU's), that differ in bedrock type, texture of surficial deposits, and land use. Additional data were collected along with the fish-community data, including measures of habitat, water chemis try, and population surveys of algae and benthic invertebrates.

Of the 20 sites, 19 are classified as trout (salmonid) streams. Fish species that require cold or cool water were the most commonly collected. At least one species of trout was collected at 18 sites, and trout were the most abundant species at 13 sites. The species with the greatest collective abundance, and collected at 18 of the 20 sites, were mottled sculpin (Cottus bairdi), a coldwater species. The next most abundant species were brown trout (Salmo trutta), followed by brook trout (Salvelinusfontinalis), creek chub (Semotilus atromaculatus), and longnose dace (Rhinichthys cataractae). In all, 31 species of fish were col lected. The number of species per stream ranged from 2 to 14, and the number of individuals col lected ranged from 19 to 264.

According to Index of Biotic Integrity (IBI) scores, S sites were rated excellent, 10 sites rated good, 4 rated fair, and 1 rated poor. The ratings of the five sites in the fair to poor range were low for various reasons. Two sites appeared to have more warmwater species than was ideal for a high-qual ity coldwater stream. One was sampled during high flow and the results may not be valid for peri ods of normal flow; the other may have been pop ulated by migrating warmwater species. Two sites had insufficient deep-water habitat to support large numbers of fish, especially top carnivores. Finally, one stream may be too cool to support enough warmwater species and too warm to support trout.

In general, two methods of evaluating site habitat indicate that habitat is not a limiting factor for fish communities. However, two sites were rated as fair according to both habitat evaluation methods due to low base flow. Two sites rated below good according to one habitat evaluation method but rated good or excellent according to the other.

Detrended correspondence analysis (DCA) of data for 17 sites showed three station groupings. These groupings fell along RHU divisions and each group was associated with one of three trout species. A species-richness gradient was evident on the station-ordination diagram. Intolerant spe cies were associated with each grouping, a reflec tion of the generally high water quality at the sites. However, no significant differences were found between IBI scores or habitat indices among the site groupings. The DCA axis 1 and 2 scores cor related with average velocity and percent pool as well as RHU factors percent sandy surficial depos its, percent wetland, percent agriculture, and bed rock. Average velocity was highest at three sites which also had among the highest measured flow and largest drainage areas. Percent pool was gen erally lower at sites with smaller percentages of sandy surficial deposits, with one exception.