Linear spawning/rearing habitat model

Streams accessible to fish may be suitable for spawning or rearing, or may only be used as movement corridors to reach such habitats. When estimating fragmentation and prioritizing further work, the amount of potential spawning or rearing habitat is of greater interest than the raw amount of corridor habitat. In addition to modelling barriers to fish passage, bcfishpass can model the intrinsic potential (IP) of streams to support spawning or rearing activities for several species (Pacific Salmon, Steelhead, Bull Trout, Westslope Cutthroat Trout).

Linear spawning/rearing habitat modelling is currently based on species specific criteria for:

• stream gradient

• channel width or discharge (depending on modelling requirments and/or data availability)

• network connectivity (rearing stream segments must have a specific type of connectivity to spawning stream segments)

• feature type (whether spawning/rearing occurs in stream / wetland / lake etc)

Per species threshold values for stream gradient and discharge/channel width are noted (and can be adjusted) in the file parameters_habitat_thresholds.csv.

Sources for these values for Pacific salmon and steelhead are documented in Table 1 of Rebelatto et al (2024). Gradient and discharge thresholds are derived from the literature and from analysis of known spawning stream characteristics. Channel width thresholds are designed to eliminate very small streams from consideration. Note that the models will tend to retain many streams that may be of marginal habitat; outputs should be used to assist prioritization for further assessment and fish passage work - not as a definitive habitat classification.

Streams with observed spawning or rearing (from FISS via bcfishobs, PSF’s Pacific Salmon Explorer, and CWF WCRP stakeholder inputs) are automatically classified as spawning or rearing regardless of stream characteristics.

Gradient

Per species spawning/rearing gradient thresholds were taken from the literature and, where unavailable in the literature, derived from known fish spawning locations.

Gradient of each stream segment is calculated as rise over run. Rise is taken from the Z value (elevation) of the endpoints of the stream segments. Run is the length of the steam segments.
Stream segments are BC Freshwater Atlas stream network features, further subdivided by other stream-referenced features used in the model (when processing the access model, streams are split at natural barriers, anthropogenic crossings, and at locations of FISS observations of species listed here - currently BT,CH,CM,CO,CT,DV,GR,PK,RB,SK,ST,WCT).

Note that stream lengths and resulting gradient will change if a new natural barrier, anthropogenic crossing, or observation is added to the database - breaking an existing segment into smaller segments. These changes to gradient can result in small inconsistencies to modelled spawning/rearing outputs for a given area over time.

Discharge / channel width

Spawning and rearing activity depends on sufficent flow to the stream. bcfishpass can be configured to use either mean annual discharge (m3/s) or channel width (m) (as a discharge proxy), depending on data availability and/or user preference. Per species spawning and rearing discharge/channel width thresholds are taken from the literature and, where unavailable in the literature, derived from known fish spawning locations.

Discharge is modelled within the Fraser, Columbia and Peace basins:

• PCIC source

• upsampling of source to FWA streams

Channel width is modelled for all of BC:

• Poisson Consulting model based on upstream area / precipitation

• data collection/preparation

NOTES

1. Discharge and channel width models are based on historic climate data

2. Contributing area (FWA watersheds) and precipitiation (ClimateBC) datasets used to model discharge / channel width are both cut off at the BC border:

   • all results from the above models are only valid for streams with 100% of their contributing area with BC

   • streams with contributing area outside of BC (and thus with invalid spawning/rearing models) ARE NOT CURRENTLY NOTED in model outputs/file distributions

Feature type and network connectivity

Before a segment can be modelled as spawning or rearing, segments with suitable gradient and discharge/channel width are further filtered by feature type and network connectivity. These criteria vary by species and life stage:

Species	Life stage	Additional feature type and connectivity criteria
Bull Trout	spawning	within streams/rivers
Bull Trout	rearing	within streams/rivers AND ( on spawning segment OR downstream of spawning segment OR on a tributary downstream of a spawning and beginning within 10m of the tributary OR <10km upstream of any spawning with no stream segment of slope >=5% between the spawning and potential rearing )
Chinook	spawning	within streams/rivers
Chinook	rearing	within streams/rivers AND ( on spawning segment OR downstream of spawning segment OR on a tributary downstream of spawning and beginning within 10m of the tributary OR <10km upstream of spawning with no stream segment of slope exceeding 5% between the spawning and potential rearing )
Chum	spawning	within streams/rivers
Chum	rearing	No rearing modelled (this species does not generally rear in fresh water)
Coho	spawning	within streams/rivers
Coho	rearing	(within streams/rivers OR wetland) AND ( on spawning segment OR downstream of spawning segment OR on a tributary downstream of spawning and beginning within 10m of the tributary OR <10km upstream of spawning with no stream segment of slope exceeding 5% between the spawning and potential rearing ) Note - Coho rearing in wetlands is not initially restricted by gradient and discharge/channel width
Pink	spawning	within streams/rivers
Pink	rearing	No rearing modelled (this species does not generally rear in fresh water)
Sockeye	spawning	within streams/rivers AND ( <3km downstream of rearing lake, with no stream segment of slope >=5% between the rearing lake and the potential spawning stream OR upstream of the rearing lake and composed of segment(s) adjacent to the rearing lake (within 2m) )
Sockeye	rearing	lakes of >= 2km2
Steelhead	spawning	within streams/rivers
Steelhead	rearing	within streams/rivers AND ( on spawning segment OR downstream of spawning segment OR on a tributary downstream of spawning and beginning within 10m of the tributary OR <10km upstream of spawning with no stream segment of slope exceeding 5% between the spawning and potential rearing )
Westslope Cutthroat Trout	spawning	within streams/rivers
Westslope Cutthroat Trout	rearing	within streams/rivers AND ( on spawning segment OR downstream of spawning segment OR on a tributary downstream of spawning and beginning within 10m of the tributary OR <10km upstream of spawning with no stream segment of slope exceeding 5% between the spawning and potential rearing )