Antarctic minke whales find ice gaps along the ice edge in foraging grounds of the Indo-Pacific sector (60° E and 140° E) of the Southern Ocean

Abstract

Antarctic minke whales Balaenoptera bonaerensis are rorquals that migrate to Antarctic waters to forage during the austral summer. Because the species frequents the edges of ice packs in summer, the potential impact of long-term physical environmental changes poses serious conservation concerns. Condition along the ice edge vary regionally, sometimes forming small ice free areas (ice gaps), and little is known about whale movement patterns associated with these small-scale variations in the physical environment. In this study, six minke whales were tracked for an average of 31 days (range 4–77 days) from January to March of 2016 and 2017 between 60° E and 140° E above and off the continental shelf. The tracking data of five animals were fitted to a Bayesian hierarchical switching state-space model assembled from ARGOS data filters to estimate behavioral states. Results show that Antarctic minke whales are likely to search for ice gaps areas and remain there for extended periods until the surrounding ice melts, rather than stay at krill rich shelf breaks or areas with high chlorophyll-a concentration. When no ice gaps were nearby, the whales were likely to move eastward along highly concentrated ice packs to find a gap. Our study found a strong association between minke whale movements and ice dynamics during the summer foraging season in this region.