Occupancy of brook trout and brown trout in streams of the mixedwood plains ecozone.
Abstract
Understanding which streams might support brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta) is valuable to conservation and resource management activities such as assessing habitat; predicting species occurrence; and informing inventory, conservation, and restoration efforts. Species distribution models offer a cost effective way to estimate where fish are without doing an exhaustive inventory across the landscape. Using presence and absence data, we developed models to predict the summertime occupancy of brook and brown trout in the Mixedwood Plains Ecozone in southern Ontario. Our results match those of previous studies and show that the important explanatory variables are mostly topographical and geological (e.g., overburden thickness, elevation), which cannot be changed through management actions. Brook and brown trout prefer streams with high base flows and cold water. Restoration efforts can focus on maintaining/improving cold base flows by reducing water withdrawals, preventing the development of recharge areas, and applying proven green infrastructure and stream restoration methods (e.g., reforestation). Trees keep water shaded and cool, extending the availability of cold water downstream, and provide habitat, stabilize stream banks, and encourage infiltration. Together, these restoration efforts can help to increase brook trout habitat and buffer populations from the effects of climate change. The competitive success of brook and brown trout varies based on the environmental context (e.g., flow and thermal regimes, water quality, climate, productivity, and network position). Understanding the environmental context and barriers that segregate species is important in assessing species interactions on the riverscape. Reduced aquatic connectivity can lead to increased risk of extinction due to environmental, demographic, and genetic stochasticity. However, increasing connectivity can invite harmful non-native species. Our model predictions about habitat suitability and overlap between brook and brown trout can be used to guide decisions about barrier removal and help balance trade-offs between population isolation and restoring connectivity. Barriers are likely needed in certain locations in stream networks, however, many are likely redundant and could be removed to enhance ecosystem resilience.