Hybridization of Southern Hemisphere blue whale subspecies and a sympatric area off Antarctica: impacts of whaling or climate change?

Understanding the degree of genetic exchange between subspecies and populations is vital for the appropriate management of endangered species. Blue whales (Balaenoptera musculus) have two recognized Southern Hemisphere subspecies that show differences in geographic distribution, morphology, vocalizations and genetics. During the austral summer feeding season the pygmy blue whale (B. m. brevicauda) is found in temperate waters and the Antarctic blue whale (B. m. intermedia) in polar waters. Here we used genetic analyses to report on several cases of hybridization between the two recognized blue whale Southern Hemisphere subspecies in a previously unconfirmed feeding season sympatric area off Antarctica. The pygmy blue whales utilizing waters off Antarctica may migrate then breed during the austral winter with the Antarctic subspecies. Alternatively, the subspecies may interbreed off Antarctica outside the expected austral winter breeding season. The genetically estimated recent migration...