Appendix 5: Rules for Defining Zones of Influence
We define Zones of Influence (ZOIs) for the spawning life stage for each salmon CU. A spawning ZOI represents the area of land that drains directly into the spawning habitat of a specific salmon CU.
To spatially define ZOIs, we use the Province of British Columbia’s 1:20,000 Freshwater Atlas (FWA) Assessment Watersheds dataset (hereafter, 1:20K FWA assessment watersheds), which is a geospatial dataset freely available online via DataBC. The rules for defining ZOIs were initially developed by the Skeena Technical Advisory Committee (Porter et al. 2013, 2014) with specific nuances that vary by species and life stage.
Spatial processing for all ZOIs has been conducted using ArcGIS Desktop 10.6 using Python scripts, which allow automatic querying of the FWA hierarchical coding systems to identify areas upslope of a given spawning area. For lake-type sockeye CU, this process identifies all of those streams that are directly upslope of spawning lakes and captures them. ZOIs for all species across all regions are manually reviewed, verified, and corrected as needed.
Lake-type Sockeye CU Zones of Influence
Spawning ZOI: For each CU, we identify the lake outlet and define an upstream ZOI by delineating the areas of all 1:20K FWA assessment watersheds that are upstream of the lake outlet. This upstream area captures the area of land which influences spawning sites for lake-type sockeye CUs.
River-type Sockeye CU Zones of Influence
Spawning ZOI: The extent of all 1:20K FWA assessment watersheds that directly intersect with known spawning locations for river-type sockeye.
Chum CU Zones of Influence
Spawning ZOI: The FWA assessment watersheds that intersect directly with known chum spawning locations delineate the spawning ZOI for each chum CU.
Chinook CU Zones of Influence
Methods for delineating Chinook CU spawning zones of influence vary by region in accordance with the CU delineation approach used by DFO. In the Skeena, Nass, Central Coast, and Haida Gwaii Regions, Chinook CUs are defined using a more restrictive geographic representation. In the Fraser, Vancouver Island and Mainland Inlets, and Columbia regions, Chinook CUs are more broadly defined geographically.
Spawning ZOI (Skeena, Nass, Central Coast, and Haida Gwaii Regions ): All the FWA assessment watersheds that intersect directly with Chinook CU locations, regardless of whether or not spawning locations were identified for Chinook within an assessment watershed.
Spawning ZOI (Fraser, VIMI, and Columbia Regions): Defined by the full extent of the 1:20K FWA assessment watersheds that directly intersect with identified spawning locations for each Chinook CU. In the Columbia region, assessment watersheds that contained spawning locations upstream of the CU boundary were included as part of the CU’s spawning ZOI.
Coho CU Zones of Influence
Spawning ZOI: Defined by the full extent of the 1:20K FWA assessment watersheds that directly intersect with identified spawning locations for each coho CU.
Pink CU Zones of Influence
Spawning ZOI: Defined by the full extent of the 1:20K FWA assessment watersheds that directly intersect with identified spawning locations for each pink salmon CU.
Steelhead CU Zones of Influence
Spawning ZOI: Defined for each steelhead CU by the full extent of the 1:20K FWA assessment watersheds within CU boundaries that directly intersect with identified spawning locations of steelhead or rivers with the presence of spawning steelhead populations identified or inferred from research by Parkinson et al. (2005).