In the Southern Hemisphere, humpback whales migrate between feeding grounds around Antarctica to breeding grounds in tropical waters, but an understanding of these stocks—divided into “Breeding Stocks A-G” for management purposes—has long been hazy because of a lack of data. But recently, researchers analyzed an unsuspecting feature of humpback whales to better understand their migration patterns: scars on their flukes.
In a new study recently published in the Journal of Mammalogy, researchers combined photographic evidence of tail flukes and dorsal fin images to gather more information about movement patterns of Breeding Stock B, which moves along Africa’s West Coast around western South Africa to Namibia and Gabon. By analyzing the scars and wounds on their tail flukes and dorsal fins—specifically from orcas and cookiecutter sharks—the scientists were able to pinpoint humpback whales’ recent migratory routes in comparison to the dispersion of orcas and cookiecutters. This study provided the first “complete comparison” of photo identification of whales between Namibia, Gabon, and western South Africa.
Researchers found that whales off Namibia had the highest amount of fresh scarring from cookiecutter sharks—which are typically found in warmer waters—than compared to whales off Gabon and West South Africa, according to the study. Because fresh cookiecutter shark wounds indicate that humpback whales had recently been in warmer waters, this revealed differentiations among migration routes. Orca whales have a worldwide distribution and their bites were more widespread among the humpback whales.
In addition, researchers found that humpback whales used central Namibia as a mid-point among their migration routes. The fact that there were low calf numbers, few competitive groups, and no singing—as humpback whales produce the longest-lasting calls of any animals—added to the evidence that Namibia does not serve as breeding grounds, according to the study.
Humpback whales are listed as endangered under the Endangered Species Act (with two populations are currently under review for delisting), though as “least concern” on the International Union for Conservation of Nature’s Red List of Threatened Species. Humpback whales previously experienced large declines from commercial exploitation, but are said to be rebounding in much of their range, according to the National Marine Fisheries Service. Current threats to these gentle giants include incidental capture in fishing gear, vessel collisions, whale watching disturbance, and more.