How would you manage 175,000 kilometers of streams for a large and diverse body of fanatical smallmouth anglers? That’s exactly the question the Missouri Department of Conservation faced in its effort to provide more opportunities in a state already known for its smallmouth streams.
To keep a finger on this vast and important fishery, biologists called on a computer system that could use readily available data to tell them where to focus management efforts. And the tool they ultimately used can also help anglers put an “X” on the map when they plan their next smallmouth trip.
Fisheries biologists turned to geographic information systems, or GIS. The technology lets researchers determine important characteristics such as soil types, stream gradient and watershed slope for any stream using existing spatial data such as soil and topographic maps.
University of Missouri fishery researchers developed a model that integrated watershed characteristics obtained by GIS analysis, information on springs, and smallmouth bass abundance data for a portion of Missouri’s streams to predict smallmouth abundance in any river segment in the state.
IDEAL SMALLMOUTH HABITAT REVEALED
The data found that smallmouth populations were more likely to occur in streams running through areas with rock and coarse-textured, permeable soils; they were less likely to occur in areas with low-permeability soils, which have high runoff and little infiltration of rainfall. Rocky watersheds have streams with rocky bottoms that provide good smallmouth habitat—shelter from current, survival of young fish and habitat that supports abundant food organisms.
On the other hand, streams flowing through watersheds with highly impermeable soils would be more likely to have wider variations in flow and may receive more sediment input and less flow from groundwater springs.
The GIS analysis further found that smallmouths were likely to be more abundant in stream segments in rocky and coarse¬texture-soil watersheds with gradual stream channel gradient, high water-input from springs, and steep watersheds. Fish were likely to be relatively abundant in higher gradient streams if they were larger waters. In other words, smallmouths were scarce in headwater streams.
The importance of locally steep watersheds is a manifestation of streams with bluff banks—smallmouth abundance tends to be high in stream segments with bluff pools. Conditions affecting the occurrence and abundance of smallmouths are largely geologic, topographic and watershed factors, things over which fisheries managers have no control. So how is this information useful?
USING WATERSHED DATA IN THE DAY-TO-DAY
For managers challenged with overseeing thousands of miles of streams, many of which offer limited access, readily available watershed data can be used to focus monetary and manpower resources in streams expected to support brown bass populations. Further, the same data can be used to establish reasonable management goals based on predicted potential.
Anglers can benefit from the technology in two important ways. First, the data drive home the fact that fishermen must have reasonable expectations. Don’t expect all streams in Missouri, or any other state with stream smallmouth resources, to have equally good bronzeback populations.
Second, fishermen can use GIS findings to help isolate the stream segments more likely to support strong bronzeback populations.
For example, start your search with rocky streams. Avoid rivers where watersheds, especially if altered by human activities, are likely to contribute a lot of sediment to the stream. Expect larger, low-gradient streams to hold more fish, and focus on segments that receive high spring flows and have bluff pools.
Dr. Hal Schramm is a biologist with the U.S. Geological Survey, Mississippi Cooperative Fish and Wildlife Research Unit, and professor of Wildlife and Fisheries at Mississippi State University.