Study shows gray whales adapted diet in times of change

Persia Salehi/Staff

A recent study by UC Berkeley and Smithsonian Institution paleontologists on past gray whale diets suggests that researchers should look to how animals survived past events, such as the Ice Age, in order to anticipate how they will deal with such extreme environmental conditions in the future.

The study, published Wednesday in the journal PloS ONE, found that by adapting and finding food elsewhere, gray whales survived over 20 cycles of intense temperature changes during the Pleistocene Ice Ages, which had caused their main food source to disappear.

Prior to and during the Ice Age, when glacial cycles were not occurring, the most visited food source for gray whales was in the Bering Plateau, between Alaska and Russia, where they still frequently feed today, according to David Lindberg, a UC Berkeley professor of integrative biology and a co-author of the study.

When the Bering Plateau dried out due to the glacial cycles, gray whales most likely survived by having a diversified diet, similar to one group of gray whales today that feeds on herring and krill found in water columns off the coast of Vancouver Island, said Nick Pyenson, a curator at the Smithsonian and a co-author of the study.

“To be genetically and ecologically distinct, gray whales feed on these water columns,” Pyenson said. “We see this as important to be ecologically flexible during tough times in where they are not forced to feed on the sea floor.”

According to the study, the Bering Sea is also one of the most productive marine ecosystems in the world and provides a primary food source seasonally to many species of crustaceans, bony fish and whales.

Pyenson said that there are about 22,000 eastern gray whales existing along the Pacific coast today, even though the population peaked at about 70,000 gray whales about 120,000 years ago.

This observed decrease in the gray whale population can be attributed to human whaling and human-mediated habitat deterioration, according to the study.
Lindberg added that what is even more interesting is that there are only a few hundred western Pacific gray whales found between the coast of China and the Sea of Okhotsk, though there is a huge feeding potential in that area.

Pyenson said he would attribute this anomaly to a long legacy of exposure to whaling, which likely decimated the western gray whale population.

Though the population has declined over time, gray whales are still considered to be one of the best examples of conservation practices, which restored their population from a few thousand after hunting to the 22,000 gray whales today, according to the study.

International whaling laws such as the U.S. Marine Mammal Protection Act of 1972 have allowed the eastern gray whale population to recover from near collapse, the study states.

“Many organisms including whales have adapted to those changes, where many of them have survived similar kinds of bad times — the problem now is to distinguish who are going to be the winners and the losers,” Pyenson said.