The California gray whale is one of the most commonly seen whales in Monterey Bay. A calf is about 17 feet (5.2 m) long at birth and 20 feet (6.1 m) long by the time it passes Monterey, heading north with its mother in the spring. Female gray whales are usually larger than males.

Conservation

Like all species of great whales, the gray whale was in danger of extinction until it became protected by law in the 1970s. This allowed the population to recover, and it was removed from the Endangered Species list in 1994. In the late 1990s, the population was as high as 26,000, but today hovers around 22,000.

Impacts of climate change, such as reduced sea ice cover, may already be affecting gray whales. Research shows that gray whales now feed farther north, and stay there longer than they have before.

A thin-ice diet

The Arctic has lost 70 percent of its sea ice in recent decades. The ice that remains is thinner than ever before, and that affects the gray whales’ food supply.

During the winter, a thick blanket of sea ice covers the surface of the Arctic, leaving the waters below in darkness. When the ice retreats, sunlight hits the sea, and tiny plants called phytoplankton burst into life. These algal blooms provide food for zooplankton, including the minuscule crustaceans and worms gray whales eat.

But climate change is causing phytoplankton to bloom earlier in the season. As Arctic ice continues to thin, the growing season might start so much earlier that the blooms grow and collapse entirely under the ice.

A new route to explore

On the positive side, melting sea ice may allow gray whales to recolonize the Atlantic Ocean, where they haven’t lived for centuries. Commercial whaling wiped out the Atlantic gray whale population in the 1800s, and sea ice has blocked the whales’ passage from the Pacific — until now. Two recent sightings off the coasts of Israel and Namibia suggest gray whales may have crossed back into the Atlantic.

“It was on everyone’s mind that this must be related to accelerated loss of ice in the Arctic,” says S. Elizabeth Alter, an evolutionary biologist at the City University of New York, York College. “Was this just a freak event, or the beginning of gray whales recolonizing the Atlantic?”

In the past, gray whales moved between the Atlantic and Pacific whenever the ice cover retreated to allow passage, according to DNA analysis by Alter and her team. Their study also found that gray whale habitat can expand as sea ice melts.

Gray whales aren’t the only animals expanding into a less icy Arctic. People are, too, as more of the sea stays open for industrial uses like shipping, oil exploration and commercial fishing. International cooperation is essential to responsibly manage these newly accessible Arctic waters.

What's next for gray whales?

Gray whales have dealt with big changes in their history: past climate change, hunting, ocean pollution, ocean noise and shipping traffic. Alter worries today’s challenges could push the gray whale population to a breaking point.

“My biggest concern for whales is that we continue to add on all these stressors, one by one. It’s time for us to take a hard look at those cumulative impacts and think about how we can reduce each of them.”

Information Provided by Monterey Bay Aquarium