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The white spots on this whale’s head are barnacles that live only on that whale species. 

Tony Wu/Minden Pictures

Hitchhiking barnacles could reveal migration routes of ancient whales

SAN FRANCISCO, CALIFORNIA—Want to know where a migrating whale has been? Just check out the barnacles on its head. As these hitchhikers grow, they pick up signatures of the surrounding ocean, providing a record of the whale’s travels, even ancient ones, researchers reported here last week at the annual meeting of the Society of Integrative and Comparative Biology.

“Not only could [the approach] be used to look for how ancient migration patterns may have changed, it could also potentially be used to tell us something about the oceans that ancient migrators were visiting,” says David Cade, an integrative biology graduate student at Stanford University in Palo Alto, California, who was not involved with the work.

Worldwide travelers, whales swim thousands of kilometers between feeding and breeding grounds. Understanding where they go, both now and in the past, is critical to conserving these leviathans. Extensive monitoring and tagging have revealed much about whale migration, but “we have little direct evidence as to their prehistoric migration habits,” says Larry Taylor, a graduate student at the University of California (UC), Berkeley.

About 40 years ago, researchers demonstrated that barnacles—sedentary, armored invertebrates—attached to gray whales recorded the path those whales take annually. That’s because the barnacles take up oxygen atoms from water, and those atoms vary in weight, according to how many neutrons they contain. Warmer water supplies a higher proportion of heavier oxygen atoms, for example.

Taylor wondered whether fossil barnacles would track the migrations of ancient whale species in the same way. Taylor focused on coronulid barnacles, which live only on humpbacks. First he confirmed that humpback whale barnacles are as informative as gray whale barnacles. He analyzed the oxygen ratios in the plates of barnacles found on a beached humpback whale. They reflected that whale’s known journey through the Pacific Ocean, he reports.

Encouraged by that finding, Taylor has since collected and analyzed small amounts of fossil coronulid barnacles from across the North and South American west coasts. Even though the barnacles are no longer attached to whales, he knows that because of the tight association between one of these barnacle species and humpbacks, these barnacles passed their lives on ancient humpbacks. 

At first blush, the barnacle data indicate the ancient humpback traveled roughly the same long distances in the Pacific Ocean as its modern counterparts, Taylor reported at the meeting. Thus, “Migration has long been a critical aspect of their ecology,” he adds.

Other researchers are intrigued by Taylor’s approach, but, “The research is in an early stage,” says Frank Fish, an integrative biologist at West Chester University in Pennsylvania who was not involved with the work. And though Daniel Costa, an ecologist at UC Santa Cruz, calls the study novel, he worries that there needs to be more oceanographic information, about ancient oceans, to predict migration routes well.

Nonetheless, in the coming months Taylor hopes to pin down exactly where whales were moving over the past 5 million years. “This work can help us better understand how migratory behavior has been affected by various climate states,” he says. He thinks that knowledge will help conservation biologists better predict how these whales may respond to current changes in climate.

*Correction, 11 January, 11:35 a.m.: The photo caption and this story have been updated.