Notes: Utility of Depth and Velocity Preferences for Predicting Steelhead Parr Distribution at Different Flows

Abstract

We tested an assumption of the instream flow incremental methodology that depth and velocity preferences are independent of streamflows. We had previously developed depth and velocity preferences (P[d\ and P[v]) for juvenile (parr) steelhead Oncorhynchus mykiss at 0.86 m-Vs in Morse Creek, Washington, and found parr distributed in microhabitats with higher combined depth-velocity preference (P[dv\ = P[d] X P[v]) at a similar flow (0.69 nvVs). In the present study, we evaluated the relationship between fish distribution and combined depth-velocity preference using an independent data set from a higher flow (2.41 m 3 /s) in the adjacent stream segment. Most steelhead parr were distributed in microhabitats with high P[dv\, consistent with distribution at 0.69 m 3 /s and significantly different than expected if fish distribution were independent of habitat preference (chi-square, P < 0.02). These results suggest that depth and velocity preferences are independent of flow.

Comment: Testing the Independence of Microhabitat Preferences and Flow (Part 1)

“…Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/ page/terms-and-conditions Beecher et al (1995) should be commended for trying to test one of the various assumptions of the physical habitat simulation model (PHAB-SIM). They noted Shirvell's (1990) report that juvenile steelhead Oncorhynchus mykiss used areas of stream with different water velocities at different flows, which suggested that the microhabitat preferences of juvenile steelhead can be a function of flow.…”

“…In an earlier study, Beecher et al (1993) developed preference criteria for depth and velocity from observations of 104 juvenile steelhead at a relatively low flow (Figure 1). In a later study, Beecher et al (1995) measured depth and velocity at regular intervals along evenly spaced transects in an adjacent reach of the same stream at a relatively high flow. This gave them data at 242 points on a grid, which they took to represent an equal number of PHABSIM cells.…”

“…To analyze the data from the later study, Beecher et al (1995) used the product (denoted P[dv]) of depth preference (P [d]) and velocity preference (P[v]) for each cell. They divided the P[dv] range, which extends from 0.0 to 1.0, into four intervals such that approximately one-fourth of the cells fell into each range.…”

“…When this hypothesis was rejected by a chi-square test, they took this result as "validating the assumption of flow-independent preferences/* The logic of this claim is not apparent. The question is not whether juvenile steelhead distribute themselves evenly in streams regardless of depth and velocity, but whether their preferences for Table 2 of Beecher et al 1995). COMMENTS 537 depth or velocity change with flow.…”

“…cm/sec) FIGURE I.-Plots of depth preference (PU/J) and velocity preference (Pfv]) for 104 steelhead parr (fromTable IofBeecher et al 1995).…”