7229 - Laserfiche WebLink

Home Browse Search

the utilization curve, resulting in preference curve coefficients. Theoret- ically, category three curves should be unconditionally transferable to any stream, although this has not been validated. At present, very few category three curves exist because most habitat utilization data sets are without concomitant habitat availability data sets. In the future, the need to collect habitat availability data will be impressed upon investigators. e Category four curves (conditional preference curves), describe habitat requirements as a function of interaction among variables. For example, fish depth utilization may depend on the presence or absence of cover; or velocity utilization may depend on time of day or season of year. Category four curves are just beginning to be developed by IFASG. HSI models generally utilize category one curves for habitat evaluation. IFIM analyses may utilize any or all categories of curves, but category three and four curves yield the most precise results in IFIM applications; and category two curves wi 11 yield accurate results if they are found to be transferable to the stream segment under investigation. If category two curves are not felt to be transferable for a particular application, then category one curves may be a better choice. For an IFIM analysis of riverine habitat, an investigator may wish to utilize the curves available in this publication; modify the curves based on new or additional information; or collect field data to generate new curves. For example, if an investigator has information that spawning habitat utiliza- tion in his study stream is different from that represented by the SI curves, he may want to modify the existing SI curves or collect data to generate new ~ curves. Once the curves to be used are dec i ded upon, then the curve co- .., ordinates are used to build a computer file (FISHFIL) which becomes a necessary component of PHABSIM analyses (Milhous et al. 1981). Availability of Graphs for Use in IFIM All curves available for IFIM analysis of white sucker habitat are category one (Table 7). Investigators are asked to review the curves (Figs. 4 to 8) and modify them, if necessary, before using them. Spawning. For IFIM analyses of white sucker spawning habitat, use curves for the time period during which spawning occurs (sometime between March and July, depending on locale). Spawning curves are broad and, if more accuracy is desired, investigators are encouraged to develop their own curves which will specifically reflect habitat utilization at the selected site. There are two approaches for determining the amount of spawning/egg incubation habitat for a given stream reach. The recommended approach for the white sucker is to treat spawning and egg incubation as separate life stages, each with its own set of criteria (Figs. 4 and 5). If the spawning/egg incuba- tion weighted useable area varies by more than 10% during the 5 to 14 day egg incubation period, then investigators may wish to determine the effective spawning habitat, using methods outlined by Milhous (1982). 40 e