The quality of physical habitat for juvenile salmonids is defined according to specifications outlined by the Water Quality Parameter and Habitat Productivity Technical Group. Habitat quality is assessed in terms of temperature, salinity and dissolved oxygen thresholds, with four categories defined for each variable.

Temperature:

optimal growth	positive growth	no/negative growth	unsuitable
\(14-18^\circ\text{C}\)	\(< 14^\circ\text{C}\) or \(18-21^\circ\text{C}\)	\(21-25^\circ\text{C}\)	\(> 25^\circ\text{C}\)

Dissolved Oxygen:

minimal impairment	some impairment	severe impairment	unsuitable
\(> 6 \text{ mg/L}\)	\(4-6 \text{ mg/L}\)	\(3-4 \text{ mg/L}\)	\(< 3 \text{ mg/L}\)

Salinity:

freshwater	isotonic	brackish	marine
\(< 10 \text{ ppt}\)	\(10-15 \text{ ppt}\)	\(15-28 \text{ ppt}\)	\(> 28 \text{ ppt}\)
Low energy demand	negligible energy demand	high energy demand (freshwater-acclimated)	unsuitable (freshwater acclimated)
		low energy demand (saltwater-aclimated)	moderate energy demand (saltwater-aclimated)

Overall Habitat

To assess the overall habitat quality of a region, the individual ratings are into the 9 categories defined below.

category	Description
Optimal	optimal or positive growth (T); minimal impairment (DO); Low or negligible energy demand (S)
Growth limited	no/negative growth (T); minimal impairment (DO); Low or negligible energy demand (S)
Impaired	optimal or positive growth (T); some or severe impairment (DO); Low or negligible energy demand (S)
Energy demanding	optimal or positive growth (T); minimal impairment (DO); moderate or high energy demand (S)
Growth limited, impaired	no/negative growth (T); some or severe impairment (DO); Low or negligible energy demand (S)
Growth limited, energy demanding	no/negative growth (T); minimal impairment (DO); moderate or high energy demand (S)
impaired, energy demanding	optimal or positive growth (T); some or severe impairment (DO); moderate or high energy demand (S)
Growth limited, impaired, energy demanding	no/negative growth (T); some or severe impairment (DO); moderate or high energy demand (S)
Unsuitable	any one of: unsuitable (T); unsuitable (S); unsuitable (DO)

Depth Zone Definitions

Habitat quality can also be assessed based on water depth, which has important implications for foraging, shelter and predation risk. The Water Quality Parameter and Habitat Productivity Technical Group has defined a separate set of habitat categories that assess habitat in terms of water depth.

Depth categories

Category	Description	Criteria
Littoral (Shallow/shoal)	High prey availability, high avian predation risk, low aquatic predation risk	\(depth < 1\text{m}\) and \(\max{(depth)} < 1\text{m}\)
Surface Limnetic	Low prey availability, high avian predation risk, high aquatic predation risk	\(depth < 1\text{m}\) and \(\max{(depth)} \geq 1\text{m}\)
Epibenthic	High prey availability, low avian predation risk, moderate aquatic predation risk	\(1\text{m} \leq depth \leq 5\text{m}\) and \(\max{(depth)} \leq 5\)
Subsurface Limnetic	Low prey availability, low avian predation risk, moderate aquatic predation risk	\(1\text{m} \leq depth \leq 5\text{m}\) and \(\max{(depth)} > 5\)
Profundal	Low prey availability, no predation risk	\(depth > 5\text{m}\)