Habitat criteria mapping is a relatively new approach that relies on ground-based mapping of available habitat within representative mesohabitat units (e.g., pool, riffle, run) for the species and life stages of interest at a specified range of flows, rather than a modeling approach based on extrapolation from transects. The habitat mapping approach involves mapping and quantifying preferred habitat for specific life stages of a selected group of "analysis species" and life stages in the study area. Criteria used to determine preferred habitat are based on values from the scientific literature for each species and life stage selected for analysis, as well as by collaboration with stakeholders and species experts. Habitat criteria values in the literature are reviewed for their applicability to the study area and to the populations and assemblages found there, and an appropriate range of values are selected. The approach can be applied in a very similar manner to MesoHABSIM (Parasiewicz 2001), or at finer spatial scale.
The habitat criteria mapping approach relies on ground-based measurements in the field and mapping of preferred habitat on digitally rectified low-elevation aerial photographs for a sub-sample of habitat units (e.g., pool, riffle, run). Suitable habitat is delineated in the field using well-defined habitat criteria for the species and life stages of interest in selected habitat units at various flows (Figure 7). The resulting polygons are transferred into a GIS framework to calculate available habitat area for each analysis species and life stage for each measured flow. Available habitat area is then extrapolated to similarly classified habitat units in the study area to estimate total habitat availability within the reach with an associated estimate of variance.
4.1.4.1 Advantages and disadvantages of approach
Use of habitat criteria mapping to assess instream flows has advantages and disadvantages relative to the other approaches evaluated, as discussed below:
Advantages
- Examines the entire reach for habitat, rather than potentially biased cross sections.
- Accepts variable quantities of input data for variable levels of accuracy.
- By estimating total area available at each flow (rather than an index), the approach allows the results of the habitat mapping to be used in population models to determine habitat-based production within a limiting factors framework by quantifying estimates of habitat area for key life stages under different flows. This provides the ability to evaluate potential population responses to changes in instream flows (e.g., effects of doubling spawning habitat while decreasing juvenile rearing habitat).
- Measurements in the field do not average water velocities, and can account for substrate-oriented organisms (e.g., bull trout) separately from mid-column ones (e.g., cutthroat trout).
- Mapping is based on habitat criteria derived from the best available information from the scientific literature and expert opinion, and is repeatable.
- It is possible to determine measurement error, and to estimate the variance of all habitat estimates.
- Compatible with calibration and validation by use of direct observation snorkel dives in areas mapped as preferred or not preferred.
Disadvantages
- Based on suitability criteria, which are often biased because they are based on site-specific habitat conditions and use of vertically averaged velocities, and they fail to account for habitat preferences that vary based on the scale that is considered.
- Can only analyze flows that are studied empirically, and cannot simulate habitat flow relationship other than measured flows.
- Does not allow for adjustment after data collection if new information regarding selected habitat criteria becomes available.
4.1.4.2 Site-specific considerations and applicability
Many of the advantages and disadvantages of this approach will depend on site-specific considerations, as discussed below:
- Can be applied accurately in hydraulically simple or complex streams. Therefore, it works well in high-gradient, boulder-dominated systems, where other methods do not work as well. However, it does not work well in areas that are too deep to wade safely.
- By using mesohabitats as sampling units, the approach is able to estimate the relationship between flow and habitat for long river reaches.
- Requires intensive, and costly, field data collection.
- Has been applied at the Carmen-Smith Hydroelectric Project (FERC Project No. 2242), on the McKenzie River, Oregon.
4.1.4.3 Selected references
Parasiewicz, P. 2001. MesoHABSIM: a concept for application of instream flow models in river restoration planning. Fisheries 26: 6-13.
Stillwater Sciences. 2006. Aquatic habitats and instream flows at the Carmen-Smith Hydroelectric Project, upper McKenzie River basin, Oregon. Final report. Prepared by Stillwater Sciences, Arcata, California for Eugene Water & Electric Board, Eugene, Oregon.
Vadas, R. L., Jr., and D. J. Orth. 1997. Species associations and habitat use of stream fishes: the effects of unaggregated-data analysis. Journal of Freshwater Ecology 12: 27-37.
Vadas, R. L., Jr., and D. J. Orth. 2000. Habitat use of fish communities in a Virginia stream system. Environmental Biology of Fishes 59: 253-269.
