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Movement rates of Antarctic blue whales from Discovery marks
Zoe R. Rand, Trevor A. Branch, Jennifer A. Jackson
Antarctic blue whales (Balaenoptera musculus intermedia) were hunted nearly to the brink of extinction during 20th century whaling. Effective management of this recovering population requires a better understanding of population structure to test the long-standing assumption that they are a single circumpolar population. We investigated this assumption by analyzing historical Discovery mark data with Bayesian mark-recovery models to estimate inter-season movement rates among the three ocean basins in the Southern Ocean (Atlantic, Indian, and Pacific), finding high probabilities of inter-season movement in almost all directions (median 0.08 to 0.28 yr-1). An estimated 59% of blue whales in the Atlantic Ocean remained there while 16% (95% interval: 1-33 %) moved to the Indian Ocean and 27% (11-34%) to the Pacific; 58% in the Indian Ocean remained there, 16% (5-31%) moved to the Atlantic and 26% (13-34%) moved to the Pacific; and 65% remained in the Pacific Ocean while 28% (18-34%) moved to the Indian Ocean, and 8% (1-19%) to the Atlantic Ocean. These high rates of movement suggest that there is little evidence for population structure arising from geographic separation between Antarctic blue whales in the Southern Ocean.