Modeling the Effects of Climate Change on the Thermal Habitat of Cusk

Cusk (Brosme brosme) is a deepwater fish species associated with high complexity seafloor habitat.  Population abundance of cusk in both US and Canada has declined over the last 40 years as a result of fishing activities and there is growing concern about the status of this species, although it is not formally assessed or managed.  In addition to pressures from fishing, climate change may affect cusk especially because the southern limit of its range in the Northwest Atlantic is in the Gulf of Maine.  We modeled the habitat of this species using US and Canadian trawl survey data using a Generalized Additive Model (GAM).  Although many factors were considered, temperature and bathymetric complexity (based on a topographic roughness index) were the most important variables in the prediction of cusk occurrence.  We used statistical downscaling of 11 global climate models to predict temperature change in two future time periods (2020-2060 and 2060-2100) for three climate change scenarios (B1, A1B, and A2).  We then used the ensemble climate model projections to project suitable cusk habitat in these two time periods under the three different scenarios.  Results suggest fragmentation of habitat and reduced connectivity between Canadian and US populations that may diminish the resilience of cusk populations.  This fragmentation occurs because of a spatial mismatch between areas with high complexity seafloor habitat and areas with suitable temperature.