7746

• UCREFRP Catalog Number: 7746
• Author: Stanford, J. A. and J. V. Ward.
• Title: Management of Aquatic Resources in Large Catchments
• USFW Year: 1991.
• USFW - Doc Type: Recognizing Interactions Between Ecosystem Connectivity and Environmental Disturbance.
• Copyright Material: NO

A prime example of the "illusion of technique" is the very popular incremental
method (IFIM) that is recommended by the U.S. Fish and Wildlife Service to determine
minimum flows to protect fisheries from the effects of stream regulation. The method is
based on field surveys that determine the area of the varial zone that is inundated at
different instream volumes (i.e., wetted usable area, WUA), along with other physical
habitat components (e.g., velocities). These data are then used to drive a sophisticated
simulation model involving target species and different flow scenarios to determine
minimum flows required to sustain fisheries (Nestler et al. 1989). The model actually
does nothing more than predict physical habitat availability for various life stages of
specific fishes and in some cases it does not appear to do that very well, among other
problems (Mathur et al. 1985, Orth and Maughan 1982, Scott and Shrivell 1987,
Shirvell 1989, Gan and McMahon 1990). However, the IFIM clearly is a refined and
standardized technique and its use has in some instances prevented chronic
dewatering of rivers. Our point is that this and other models are not responsive to
processes that ultimately determine variability of bioproduction and other important
aspects of ecosystem connectivity (Figures 4 and 5). In spite of warnings to the
contrary by the authors of IFIM (and other standardized approaches), the illusion for
naive users in this case is that WUA is deterministic, when in fact complex interactions
of abiotic and biotic components comprising a river are naturally stochastic. This of
course is precisely why the ecosystem exists in a quasi-equilibrium state. Naive
managers and administrators easily confuse quantification, objectivity and
sophistication with biological reality and such illusions should not be fostered (R.
Behnke, Colorado State University, unpublished).
A more rationale approach is to recognize and appreciate the complexities of
river catchments and utilize standardized tools and models in the limited sense for
which they were designed. No model or other deterministic construct likely will ever
accurately predict ecosystem structure and function at the catchment scale. But, model
building is one very effective way to better plan and articulate the need for collection of
long-term ecological data that will ultimately explain observed variability caused by
natural and human disturbances. In almost all assessments of cumulative impacts at
the catchment level, long-term empirical data describing ecosystem structure and
function are required as baselines to firmly quantify environmental change.
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