Presence of Southeast Pacific blue whales (Balaenopteramusculus) off South Georgia in theSouth Atlantic Ocean

Resumen: The Southeast Pacific (SEP) or Chilean blue whale popula-tion is largely distributed between Northern Chilean Patago-nia and the Eastern Tropical Pacific. Off South Georgia (SG),the majority of blue whales caught were Antarctic bluewhales, but recent genetic and acoustic records indicate thepossible presence of SEP individuals. To assess the presenceof SEP blue whales off SG, we carried out new analyses ofacoustic data previously reported as containing pygmy bluewhale song and analyzed the length frequencies from 20thcentury catch data. The month of acoustic data reported tocontain the presumed pygmy blue whale song was exam-ined (August 2006), and 13 days were found to have songswhich visually and quantitatively matched SEP2 songs fromNorthern Chilean Patagonia. The fundamental frequency ofSEP2 song off SG, however, was not in line with the predicted frequency shift trend of the SEP2 songs in theSEP. A mixture analysis of lengths in historic whalingcatches indicated that 3.3% of the catches from SG couldbe SEP blue whales, although this declined to 0.6%, 95% CI[0.0, 2.6] when fit to nonrounded lengths. Our results sug-gest that any SEP blue whales off SG are likely rarevagrants, at the edge of an endangered population.