Modeling habitat use by bowhead whales in response to past and future Arctic climate change

Background/Question/Methods

The effects of climate change are projected to be disproportionately pronounced in polar regions, where changes in the concentration and extent of sea ice will affect the spatio-temporal dynamics of the marine planktonic ecosystem. The endangered bowhead whale (Balaena mysticetus) is one of the largest animals in the Arctic, yet they feed on some of the smallest arctic animals, zooplankton. Changes in the abundance and distribution of zooplankton due to changes in sea ice would have direct effects on bowhead whales.

The objective of our research is to improve understanding of how the arctic planktonic ecosystem and sea ice affects the regional distribution of bowhead whales in the Beaufort and Chukchi seas, and to develop hindcasts and long-term forecasts of bowhead whale distribution under different arctic climate change scenarios.

Our approach combines a multi-decadal bowhead whale survey dataset with modeled environmental data from the pan-Arctic Biology/Ice/Ocean Modeling and Assimilation System (BIOMAS) – a fully coupled 3D model with an 11-component lower-trophic model that includes three zooplankton groups (microzooplankton, copepods, and predatory zooplankton).

Results/Conclusions

We used 23 years of aerial survey data and BIOMAS model output to train monthly bowhead whale species distribution models for the Beaufort Sea. Mean model performance as measured by AUC was 0.82. The most influential co-variate was bathymetry (30%). Zooplankton prey groups were the most influential modeled environmental co-variates: predatory zooplankton (15%), microzooplankton (13%) and copepods (12%). Sea ice, diatoms and silicates had little influence on modeled distributions. Understanding the link between secondary productivity and loss of sea ice is a necessary step to assessing the impact of increased human activities in the Arctic, such as seismic exploration, offshore drilling and commercial vessel traffic.

In the next phase of our work BIOMAS will be used to project the future responses of Beaufort and Chukchi seas' marine production cycles and food web dynamics in correlation with the continued decline in sea ice cover under the IPCC global climate model. BIOMAS predictions will then be used to drive species distribution models for bowhead whales. This type of scenario study will help us understand the potential changes in bowhead whale habitat and help evaluate strategies for minimizing human-whale interactions as sea ice extent and whale populations change in the coming decades.