Abstract

Eastern South Pacific humpback whales (Megaptera novaeangliae) migrate to three distinct mid- to high-latitude feeding areas. While movements between local breeding sites have been reported, interchange among the feeding areas has not been documented and thus has assumed not to exist. Identifying photographs of 187 humpback whales in the Magellan Strait were compared with 2,553 whales from the Antarctic Peninsula feeding area, resulting in two matches. Additionally, 37 skin samples collected at the Magellan Strait were analyzed for carbon and nitrogen stable isotopes, resulting in evidence that two other individuals traveled to the Antarctic Peninsula. Our findings provide the first known evidence of interchange between two of these feeding areas in the eastern South Pacific. The data suggest a very limited interchange, but demonstrate that some whales may permanently leave the Magellan Strait, or perform short, round-trip movement between these areas. This previously undocumented interchanges do not necessarily change existing management recommendations that the Magellan Strait is a demographically independent feeding area, but does suggest that future abundance estimate models should assume low immigration rates. Further research to better understand the extent and frequency of interchange in the austral region of South America is needed, as this will further clarify the population structure of these whales leading to more accurate scientific knowledge supporting the conservation and management of the species.