Out in the deep waters of Monterey Bay, gray whales will be swimming home later this month after a brief winter vacation in Baja California.
Whale watchers and marine scientists say these whales have been delaying their southern sojourns and point to climate change as the culprit.
Rising sea temperatures have disrupted the animals' home habitat in the waters between Alaska and Russia, said Wayne Perryman, a researcher at the Southwest Fisheries Science Center in La Jolla. Because of these changes, the whales are spending more time in the north before they start their yearly swim south.
The scientists at the center have observed the whales for more than 20 years as they pass through Monterey Bay. Compared to two decades ago, Perryman said, the animals are reaching the bay a week later.
"This isn't trivial," Perryman said. "It's a significant change."
Richard Ternullo, a boat captain for Monterey Bay Whale Watch in Monterey, said the whales' yearly arrival in the bay fluctuates, but he has noticed on average it has drifted about 10 days later into the year.
"Last year, they were considerably late," Ternullo said. "But this year they seem to be on time."
Every year, gray whales undertake a 12,000-mile round-trip swim from the frigid Bering Sea to the warm waters off Baja California. Scientists don't fully understand what motivates this epic migration -- the longest for any mammal -- but believe the animals may leave their homes to avoid predators such as killer whales, which feed on gray whale calves.