Data from: Hierarchical Bayesian model reveals the distributional shifts of Arctic marine mammals

Aim: Our aim involved developing a method to analyze spatiotemporal
distributions of Arctic marine mammals (AMMs) using heterogeneous open
source data, such as scientific papers and open repositories. Another aim
was to quantitatively estimate the effects of environmental covariates on
AMMs’ distributions and to analyze whether their distributions have
shifted along with environmental changes. Location: Arctic shelf area. The
Kara Sea. Methods: Our literature search focused on survey data regarding
polar bears (Ursus maritimus), Atlantic walruses (Odobenus rosmarus
rosmarus) and ringed seals (Phoca hispida). We mapped the data on a grid
and built a hierarchical Poisson point process model to analyze species’
densities. The heterogeneous data lacked information on survey intensity
and we could model only the relative density of each species. We explained
relative densities with environmental covariates and random effects
reflecting excess spatiotemporal variation and the unknown, varying
sampling effort. The relative density of polar bears was explained also by
the relative density of seals. Results: The most important covariates
explaining AMMs’ relative densities were ice concentration and distance to
the coast, and regarding polar bears, also the relative density of seals.
The results suggest that due to the decrease in the average ice
concentration, the relative densities of polar bears and walruses slightly
decreased or stayed constant during the 17-yearlong study period, whereas
seals shifted their distribution from the Eastern to the Western Kara Sea.
Main conclusions: Point process modelling is a robust methodology to
estimate distributions from heterogeneous observations, providing
spatially explicit information about ecosystems and thus serves advances
for conservation efforts in the Arctic. In a simple trophic system, a
distribution model of a top predator benefits from utilizing prey species’
distributions compared to a solely environmental model. The decreasing ice
cover seems to have led to changes in AMMs’ distributions in the marginal
Arctic region.