Gray whales are known for their globetrotting, migrating huge distances between their feeding grounds in summer and their calving grounds in winter. But scientists were recently surprised to discover that some gray whales from a critically endangered population in Asia cross the Pacific every year to winter off the coast of North America. This unexpected discovery has important implications for managing these endangered whales. It also highlights the fact that, even after years of study, much about these great creatures remains unknown.
Dave Weller, a marine mammal biologist at NOAA’s Southwest Fisheries Science Center, has spent years studying gray whales off Sakhalin Island in Russia’s remote Far East. These whales are critically endangered—there are only about 150 of them left—and protecting their migratory routes and calving grounds is key to their recovery. But because there are so few of them, they are seldom seen once they disperse, and so their movements are mostly unknown.
"Where do they go and how do they get there? What are the habitats they rely on when giving birth and taking care of their young?" asks Weller. "These are the mysteries that motivate me as a scientist."
During the 20th century, gray whales were hunted nearly to extinction. Today, there are only two surviving populations. The Eastern North Pacific population spends the summer getting fat on krill in the rich waters of the Arctic, then migrates along the west coast of North America to Baja California, Mexico, for the winter calving season. This population has recovered steadily since the hunting of gray whales was banned in 1946, and now numbers about 19,000.
The whales that Weller studies off Sakhalin Island comprise the Western North Pacific population. This population never recovered, and models show that they could die out within 40 years if they are not adequately protected from hazards on their summer feeding grounds, along their migratory routes, and at their calving grounds.
There have been rare sightings of Western North Pacific whales off the coasts of Japan and China, so some apparently head south along the Asian coast in winter. But in 2010, researchers from Oregon State University and the Russian Academy of Sciences tagged a male gray whale with a satellite transmitter near Sakhalin Island and then watched, surprised, as he made his way to the coast of Oregon. The next year, a tagged female made the same journey.
Once thought to be extinct, an endangered western North Pacific gray whale breaches off Sakhalin Island, Russia.
A gray whale displays its fluke as it prepares to dive under water.
Were these two whales just a couple of rolling stones, or do gray whales commonly cross the Pacific? Tagging whales is difficult, and researchers are seldom able to tag more than one or a few, so other methods are needed to answer this question. Since gray whales are individually recognizable by their pigmentation patterns, photographic matching can help.
In a painstaking effort that can only be described as heroic, Weller and his colleagues sequentially compared each of 181 photos of whales near Sakhalin Island with more than a thousand photos of whales off the coast of North America. They found ten matches. Because most of the whales that winter on the North American coast do not appear in the photo catalog, the number of matches turned up in this study is probably only a fraction of the number of gray whales that cross the Pacific.
This study,which was published last month in the journal Endangered Species Research, raises a number of questions. Are the Eastern and Western populations interbreeding, and if so how much? Are the whales that cross the Pacific native Sakhalin Islanders and just tourists in North America, or is it the other way around?
The answers to these questions will shape future conservation plans, and NOAA biologist Aimee Lang is using genetic studies to get some answers. Lang, who is also based out of NOAA’s Southwest Fisheries Science Center, is analyzing tissue samples from gray whales on both sides of the North Pacific to better understand the population structure of the Sakhalin whales and their degree of genetic mixing with the Eastern Pacific group.
Weller, meanwhile, has turned his attention to the Sakhalin whales that winter off China and Japan, areas with intense coastal development that may be inhospitable to this inshore species. How many go down there, and what conditions do they find? “That’s a critical piece of information that we don’t know anything about,” says Weller, “and it could be the key to whether that population recovers or not.”
Much about the lives of these animals remains a mystery, and multiple tools are required to unravel it—photographic matching, genetic analysis, and satellite telemetry among them. And only long-term monitoring can build the photographic catalogs and genetic databases that give these tools their power. By continuing this research, and by applying newly discovered information to conservation plans, scientists hope to make possible a world where there are two healthy, thriving populations of gray whales rather than just one.
*Please note: the above article was reposted from the NOAA Fisheries Service homepage.