High historical movement rates of Antarctic blue whales on Southern Ocean feeding grounds estimated from Discovery mark data

Little is known about Antarctic blue whale ( Balaenoptera musculus intermedia ) movement and migration. In many baleen whales, distinct populations arose due to inherited fidelity to migration routes between breeding and feeding areas. To assess whether population structure is present in the form of feeding area fidelity in Antarctic blue whales, we analyzed historical Discovery mark-recovery data with a multistate model to estimate historical interyear movement rates among the 3 ocean basins in the Southern Ocean (Atlantic, Indian, and Pacific) during 1926-1963. We found high probabilities of interyear movement in almost all directions: for blue whales in the Atlantic basin of the Southern Ocean, we estimated that each year 15% (95% interval: 0.66-46%) moved to the Indian and 29% (4-49%) to the Pacific basins; from the Indian basin, 13% (3-33%) moved to the Atlantic and 32% (14-48%) to the Pacific basins; and from the Pacific basin, 28% (13-46%) moved to the Indian and 8% (0.9-24%) to the Atlantic basins. These high estimated movement rates provide little evidence for population structure arising from basin-specific feeding ground fidelity by Antarctic blue whales.