Estimating North Atlantic right whale prey based on Calanus finmarchicus thresholds

The planktonic copepod Calanus finmarchicus is a fundamental prey resource for the critically endangered North Atlantic right whale (Eubalaena glacialis). Rather than modeling C. finmarchicus abundance broadly, this study models the environmental conditions associated with prey densities that exceed nominal right whale feeding thresholds (“τ-patches”), since whales forage based on whether prey aggregations exceed an energetic threshold rather than on abundance alone. Using a random forest model with bathymetry, temperature, salinity, day of year, chlorophyll, and current covariates, model performance was highest at a threshold of 10,000 copepods m⁻². High-density aggregations showed different environmental associations than previous abundance-based models, including a warmer favorable temperature range and higher spatial variability. The resulting prey field is designed to link directly with existing right whale density models used in US governmental decision support tools.