Killer Whale Genetics: Redefining Stock Structure in a Marine Top Predator

July 11, 2013 — Found in every ocean around the world, killer whales are a force to be reckoned with globally. Their remarkable social bonds and sophisticated hunting techniques make them top predators in their salty domain. For many years, it was assumed that these clever, highly mobile whales bred with each other freely in the seemingly homogeneous ocean. As our understanding of the oceans' complexity has grown, and dedicated researchers have peered ever deeper into the world of killer whales, it has become clear that the truth is far more nuanced.

As the agency responsible for conserving and managing killer whales in U.S. waters, the National Oceanic and Atmospheric Administration (NOAA) faces a major challenge -- it must identify orca subpopulations, understand their needs, and develop effective and sometimes unique ways to manage them. Figuring out the patterns of similarity and relatedness coded in the whales' DNA also gives managers important insights into how these subpopulations arose, what factors shaped them, and what drove divergence in the species complex. This work has implications beyond identifying the boundaries of whale stocks. It is fundamental for evaluating the status of killer whale populations.

Recent studies have shown that distinct groups of killer whales gather in the same place seasonally. Previously, scientists didn't know whether this was attributable to feeding or mating patterns. Now, genetic evidence and observations of individual whales have shown that these whales exhibit low levels of "gene flow" -- breeding among subpopulations. A new paper by NOAA scientists available via Open Access in the Journal of Hereditysheds light on these principles at work among killer whales in Alaska and the northern North Pacific Ocean.

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