A Habitat Model for Fish Communities in Large Streams and Small Rivers

Table 2

Habitat definitions and optimal ranges for 11 variables that serve as specifications for rehabilitating streams and small rivers. The manner that species model variables were consolidated and the key to plots are provided in Figure 1.

Parameter	Figure 1 panel	Habitat range	Optimal range	Synthesis comments
Mean water temperature (C) in mid-summer.	(a)	12–33	23–28	Most models specified mean temperatures forming a habitat and optimal range. The breakpoints were averaged. Most species were within the habitat range and approximated the optimal range.
Minimum dissolved oxygen (mg/l) in mid-summer.	(b)	≥1.0	≥5.5	All models showed a rise in quality from about 1 mg/l as a minimum to an optimal range without a maximum. Averages defined breakpoints. Some species went down to zero, which was unsuitable. There was much consistency for dissolved oxygen.
Annual acidity (hydrogen ion concentration, pH).	(c)	4.7–9.8	6.6–8.6	The models specified similar values for habitat and optimal ranges. The breakpoints were averaged. There was good consistency for pH.
Turbidity (nephelometric turbidity units, NTU), maximum monthly mean.	(d)	47–174	<47	Models indicated declining quality with increased turbidity beyond an optimal range. Average were used to define the optimal and tolerable levels. Conversion of measurements and statistics revealed a consistent habitat definition and optimal range for most species.
Mean water temperature (C) during most common reproduction season, spring.	(e)	12–28	17–22	Most models specified mean temperatures forming a habitat and optimal range during the spring fish reproduction season. Most species were within the habitat range. All species had a dome-shape-relation between habitat quality and temperature. Averages defined breakpoints.
Dissolved oxygen (mg/l) during the spring reproduction season.	(f)	≥1.5	≥6.2	All models showed a rise in quality from 1.5 mg/l as a minimum to an optimal range without a maximum. Averages defined breakpoints. There was consistency for dissolved oxygen.
Mean current velocity (cm/s) in riffle habitats during the spring reproduction season.	(g)	1–97	29–62	Models defined a habitat and optimal range for riffle velocity for spawning and young during the spring. The breakpoints were averaged. There was some variability in in riffle velocities, but the habitat and optimal range approximated most of the species.
Mean current velocity (cm/s) in pool habitats during the spring reproduction season.	(h)	0–24	≤8	Models defined a habitat and optimal range for pool velocity for spawning and young during the spring. Averages were used to define the range. There was some variability in pool velocities, but the habitat and optimal range approximated most of the species.
Maximum riffle water depth (cm) during the spring reproduction time.	(i)	0–87	15–31	Models varied in specifying water depth for spawning and larval rearing. The models specifying water depth range were averaged. There was some variability in riffle depths but the habitat and optimal overlapped most species models.
Portion (%) of waterway with cover for fish and food organisms.	(j)	0–100	31–61	Models defined a habitat and optimal percentage of area with cover. Average was used to define breakpoints. There were many species that had this habitat variable and most HSI models were similar to the ranges.
Portion (%) of waterway that is slow water: pools and backwaters.	(k)	1–100	44–70	Models defined a habitat and optimal range of area composed of slow and standing water at common flows. The breakpoints were averaged. The optimal habitat condition included the range for most species.