Prioritizing conservation actions by assessing lake-specific vulnerability to loss of coldwater fish habitat
Cisco (also called tulibee) are a coldwater fish that is commonly considered a prey fish in inland Minnesota lakes (in the Great Lakes, a commercial fishery exists for cisco). Decades of declines in Minnesota have led to a coordinated effort to preserve cold, oxygen rich lake habitats by limiting land use conversion in forested watersheds. This work is a leading example of climate adaptation in North America—and maybe the world—with millions of dollars of public funds used to protect forested watersheds of cisco lakes.
But not all lakes need the same protections, and accounting for the effects of climate change requires a more nuanced approach. We applied the safe operating space concept (shown at right) to oxythermal habitats as functions of watershed disturbances and increasing temperatures. In the figure to the right, a lake’s total resilience (ability to change temperature or watershed disturbance without crossing the suitable habitat threshold) was used to classify lakes into management categories for maintenance of suitable habitat.
To apply the safe operating space concept, we classify where lakes fall with respect to the quality of their oxythermal habitat (Tiers 1-3, 1 being most suitable, 3 being least suitable) using a landscape wide predictive model of cisco occurrence based on lake bottom shape (geometry ratio), mean summer air temps, and watershed development.
We can predict TDO3 (and habitat Tier) as a function of air temperature, watershed land use, and lake morphometry. We can use these predictions to assess how likely a lake is to lose habitat given projected changes in temperature, or under different scenarios of watershed land use. This enables identification of lakes that are targets for protection or restoration
We then use future climate models to estimate the July air temperature change expected at these lakes, and compare that to the temperature change required to shift the lake to a lower habitat tier. This contrast between predicted change and estimated resilience provides us with a metric by which we can assign management categories or prioritizations from the sustainable operating space concept.
