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Testing a Distributional Monitoring Approach in the Little Nahanni River watershed, NWT
Aquatic environments in northern Canada face increasing pressure from multiple stressors including climate change and expanding development. Arctic Grayling (Thymallus arcticus) are a widely distributed, but sensitive northern species that play an important role in stream ecosystem functioning. An improved understanding of Arctic Grayling distribution and habitat requirements is needed in order to assess their vulnerability to impacts, establish thresholds for development activities, and evaluate species trends over time. However, resource managers require rapid, cost-effective, and defensible methods to accurately monitor the status of stream salmonids and to protect key habitats in remote areas.
In the summer of 2014, distributional monitoring techniques based on species occurrence were tested in the Little Nahanni River watershed, Northwest Territories. Fish occurrence and a suite of habitat variables were collected at randomly selected sample sites within suitable habitat patches. Arctic Grayling were detected in 33% of the patches and 14% of sites surveyed. Sites with Arctic Grayling had average water temperatures of >10oC, average elevation <1100m and an average slope of ≤0.02. In contrast Arctic Grayling were absent from sites with average water temperatures of <6oC, elevations of >1250m and slopes of ≥0.06. Using the information collected from this distributional monitoring approach we were successful in revealing habitat thresholds that appear to drive Arctic Grayling occurrence and distribution in the watershed. Water temperature was a the most significant variable in predicting Arctic Grayling occurrence, showing an increase in the probability of occurrence at water temperatures >8oC. Further testing is required to refine the environmental and biological criteria used to define and identify suitable habitat patches and to improve detection efficiency using this monitoring approach.