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Upper Midwest Environmental Sciences Center

River Productivity

The Importance of Off-Channel Areas to Fish Production

Backwater areas provide critical winter habitat that supports fish production. (photo - Pool 10)

Backwater areas provide critical winter habitat that supports fish production.

We hypothesize that geomorphometry of the river system and the resulting relations among the main-channel, off-channel aquatic areas, and adjoining floodplain are critical to the biological production. Several lines of evidence suggest that overwintering habitat may limit some species including bluegill, crappie, and largemouth bass. Routine Long Term Resource Monitoring Program monitoring data, focused studies conducted by Upper Midwest Environmental Sciences Center (and others), and informal observations by resource managers all indicate that off-channel areas (backwaters) of the Upper Mississippi River System are often unsuitable for overwintering fish. However, the temporal and spatial distribution of these problems, the processes that contribute to them, and the actual needs of overwintering populations are not well quantified.

The need for overwintering habitat and its availability to aquatic biota in the Upper Mississippi River System (UMRS) cannot be measured directly because of system size and complexity. Thus, a scientifically sound framework is needed to make broad scale extrapolations and develop reliable estimates of winter habitat supply and demand across the system.

We believe that the physical-chemical configuration of the system can be used to predict or estimate the habitat available for aquatic plants and animals in the UMRS and that this, in turn, can be combined with biological monitoring data to assess the role of habitat limitation in biological production. Our work since 1996 has used this approach to combine geographic information system technology, routine monitoring data, and focused field studies to develop a framework (model) for predicting the distribution of overwintering habitat. Although the model we have developed thus far appears quite successful in predicting the occurrence of suitable and unsuitable overwintering habitat (as defined by water temperature, dissolved oxygen concentration, and flow velocity) in Pool 8 during a single winter, we have not tested it against winter data from other years or other areas outside of Pool 8.

A parallel approach to the problem looks for evidence of habitat limitation at a broad spatial scale among the six study reaches of the Long Term Resource Monitoring Program. The results suggest that off-channel habitat may be limiting to the production of bluegill, crappie, and largemouth bass, but only in reaches that comprise less than about 5% of the total aquatic area, such as the southernmost pools and the unimpounded Mississippi River.

This project is scheduled for completion in September 2007.

Principal Investigator: Jim Rogala

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Page Last Modified: December 21, 2010