Fisheries and Oceans Canada and Yukon Placer Secretariat
The Yukon Habitat Suitability Model predicts the suitability of habitat for Chinook salmon in reaches and watersheds within the Yukon Territory. The model uses a spatial hydrologic dataset of the Yukon Territory and scores reaches and watersheds for salmon habitat suitability based on key environmental indicators. The goal of the model is to inform the Yukon Placer Secretariat initiative to revise the effluent standards for placer mining in the Territory. Since its delivery in the fall of 2006, the model is being used actively to produce maps of predicted Chinook salmon habitat for public consultation sessions with First Nation and mining organizations as a tool for communicating where and how new placer mining standards should be established.
The model covers 16 watersheds within the Yukon Territory that drain into the mainstem of the Yukon River (Figure 1). Unprocessed spatial data for watercourses, elevation, water quality, salmon spawning areas and mining development were obtained and corrected to produce an integrated, topologically connected, dataset. In this form, the data in the model can be used for network analysis to estimate fish passage and water quality effects related to the dispersion of mine effluent.
The final dataset contains approximately 840,000 reach segments and 80,000 water bodies. Correction of the data involved three staff for approximately four months of geo-processing, and used a variety of GIS software tools. These data are stored in separate Access personal geodatabases; one for each watershed.
The model itself is coded in Visual Basic for Applications (VBA) using the ESRI ArcObjects spatial object model in ArcView 9.2. A custom user interface (Figure 2) coded in VBA allows users to change model inputs, run the model and configure the outputs, including production quality maps with scale bars and legends etc.
Habitat calculations are divided into two sub-models (Figure 3). The reach sub-model predicts the habitat quality for Chinook salmon for individual reaches. Each reach is represented in the GIS using a single line feature with several attributes that drive the model. The three main attributes are gradient, proximity to spawning areas and water quality. Running the reach sub-model looks up these attributes for each reach and assigns scores; these scores are summed to determine the overall reach habitat suitability from Low to High. Special modifiers (white boxes in Figure 3) capture a priori knowledge that overrides the basic scoring system and determines the score for special conditions (such as reaches in very steep gradients or long distances from spawning areas).
The watershed sub-model determines the overall designation of each watershed in terms of its sensitivity to impacts from placer mining. This sub-model uses four criteria: three physical and one biological. The physical criteria capture the degree to which the reaches that are valuable to Chinook salmon habitat are impacted by present or historical placer mining activities. The biological criteria capture the local expert knowledge of the overall fish distribution within the watershed. Like the reach criteria, those for the watershed model are classified into bins and assigned scores. The scores are then summed to produce a final watershed value from 3 to 18. Watersheds with a score of 10 or lower are designated as Type B, while those with a score of 11 to 18 are scored as Type A. These two designations are then used to assign different placer mining effluent standards to the two types of watersheds. Each standard provides for different maximum effluent loadings for each type of reach identified by the reach model.
During 2007, the Yukon Placer Secretariat and the Whitehorse office of Fisheries and Oceans Canada explored possibilities for improving the model and extending it to further watersheds and fish species within the Territory.