Global warming has caused changing climate conditions in the Arctic and gray whales in the Pacific, were once three to five times as plentiful as they are now were long thought to have fully recovered from whaling.
Today's population of more than 22,000 gray whales has successfully been brought back from the threat of extinction, and is now the most abundant whale population on the North American west coast, but it is far below the original number - estimated by genetic methods at 96,000 animals - that once roved the Pacific waters.
The study further found that the lowered numbers of gray whales no longer played their normal role in ocean ecology, and that the genetic variation among the whale population was too great.
"Our survey uncovers too much variation for a population of 22,000. The overabundance of genetic variation suggests a much larger population in past centuries," said Steve Palumbi, the Harold A. Miller Professor in Marine Sciences at Stanford's Hopkins Marine Station.
"The study uses computer-based genetic simulations to show that the level of genetic variation is instead more likely to be from a past population of 76,000 to 118,000 animals (with an average of 96,000)," Prof. Palumbi said.
Lead author, S. Elizabeth Alter said, a vastly reduced population of gray whales had likely exerted large changes in Pacific Ocean ecosystems.
Unique among whales, the gray bulldozes the oceans, digging troughs through the sea floor for food. In the process, they resuspend ocean sediments bring food to the surface.
"A population of 96,000 gray whales would have resuspended 12 times more sediment each year than the biggest river in the Arctic, the Yukon, and would have played a critical role in the ecology of the Bering Sea," said Alter.
"Other species may have felt the loss of whales as well. The feeding plumes of gray whales are foraging grounds for Arctic seabirds. Ninety six thousand gray whales would have helped feed over a million seabirds a year," added Prof. Palumbi.
The study appears in the Proceedings of the National Academy of Sciences (PNAS).