After 15 years of research in the waters of the South Atlantic and Indian Oceans, an international team of scientists has unveiled the largest genetic study of humpback whale populations ever conducted in the Southern Hemisphere. The team includes researchers from the Wildlife Conservation Society, the American Museum of Natural History, and other organizations. Their study appears in PLOS One, an interactive open-access journal for scientific and medical research.
By analyzing DNA samples from more than 1,500 whales, researchers can now peer into the population dynamics and relatedness of Southern Hemisphere humpback whales as never before. Though humpbacks in the Northern Hemisphere are widely studied, until now, scientists have understood much less about the interactions between populations in the Southern Hemisphere. Their findings will help guide management decisions in the sometimes politically charged realm of whale conservation.
The scientists collected skin samples from 1,527 whales at 14 sites. These whale populations are known as Breeding Stocks A (Southwest Atlantic Ocean), B (Southeast Atlantic Ocean), C (Southwest Indian Ocean), and X (Northern Indian Ocean), based on information amassed and designated by the International Whaling Commission. To obtain the samples, the researchers used biopsy darts fired from crossbows, which do not harm the whales and bounce off their bodies as they surface to breathe. Samples also came from skin that the animals slough off in the water.
Once collected, the samples were brought to the lab at the AMNH Sackler Institute for Comparative Genomics and examined through a technique called polymerase chain reaction. This method “amplifies” specific regions of DNA that can help demonstrate gene flow between populations. The research team focused on mitochondrial DNA, which is passed through maternal lines of a population, in order to measure interchange between groups.
The findings so far have revealed which whale populations interbreed and interact. For example, one or two whales swim from one side of the African continent to the other (Atlantic to Indian Oceans) every year to mate with whales outside of their group. By contrast, humpbacks on opposite sides of the Atlantic—including one population along the coast of Brazil and the other along Southern Africa—have only slightly similar genes, which indicate they have fewer interactions. However, the similar songs of the two populations do hint at interchange between the two groups, most likely in the whales’ feeding grounds in Antarctic waters.
Scientists also confirmed that the small population in the northern Indian Ocean off the Arabian Peninsula is the most distinct in terms of genetics and migratory behavior. Unlike the other humpback populations, it is non-migratory and only distantly related to the nearest group of humpbacks. As an insular group numbering fewer than 200 whales, this population is unique and therefore a conservation priority.
The study also gives scientists some insight into the mysterious and mercurial nature of ocean ecosystems, with currents, water depth, and other unseen factors serving as shifting conduits and barriers between marine populations.
The research offers a powerful conservation tool for marine biologists. “Molecular technology gives us a window into the lives of whales that can help us understand the ecological forces shaping their movements and distribution,” said Howard Rosenbaum, director of the WCS-Ocean Giants Program and lead author of the study. “We can also use our findings to inform management decisions for a species that is only now beginning to recover from centuries of commercial whaling.”
The Eppley Foundation For Research, Flora Family Foundation, and Lenfest Ocean Program provided generous support for this study. Scientific contributors to the study include: Columbia University; University of Pretoria; Environment Society of Oman; Instituto Baleia Jubarta and PURCS (Brazil); University of Cape Town; Marine and Coastal Management (South Africa); Faculdade de Biociências; Agence Nationale des Parcs Nationaux (Gabon); Association Megaptera (France); Université de La Rochelle (France).
Read the press release: 'Whale-sized' Genetic Study, Largest Ever for Southern Hemisphere Humpbacks