These and other findings on blue whales will be presented on Thursday, Feb. 14, by Oregon State University marine mammal expert Bruce Mate at a meeting of the American Geophysical Union's Ocean Sciences division in Honolulu.
Since 1993, Mate and his colleagues have tagged one hundred blue whales off the California coast and tracked their movements by satellite. They found that blue whales travel rapidly from one feeding area to another, and continue to feed throughout the entire year. Other whales, including grays and humpbacks, stop feeding during their late fall migration and while at their winter breeding grounds -areas that, in comparison to their summer feeding areas, are “biological deserts,” Mate said.
“These blue whales move fast,” said Mate, who directs the Marine Mammal Program at Oregon State University. “They are like a streak. They can't afford to waste a lot of time in low-density food zones, so they really move from one high productivity area to another.”
During the strong El Nino of 1998, about half of the blue whales Mate saw were visibly emaciated. Their rapid movement in search of food and their normally huge fat reserves are adaptations that help them survive such events, Mate pointed out.
The feeding habits of these California blue whales in fact dictate much of their behavior, Mate said. Like other whale species, they begin migrating southward in the fall, but individual whales stop when they encounter good feeding zones and may stay there for weeks at a time, whereas many other whales species migrate en masse and do not make such stops. Even the blue whales’ winter destination and likely calving area - a region off Central America called the Costa Rica Dome - is a fertile upwelling site rich with krill.
By contrast, most gray whales head to the warm waters of lagoons along the Pacific coast of Baja California for calving, while humpbacks head to Hawaii. The warm waters in these areas help conserve body heat of newborn calves, but neither location has much in the way of food for the adults.
Much of these data about blue whales is new, Mate said. Despite being the planet’s largest animals, little was known about the migration and winter habits of blue whales until scientists developed new technologies to study them.
Many of these new tools - including the tags - were developed at Oregon State University.
“In the old days, we would tag a whale and have to follow it by boat to stay within five miles, because that’s how far the signal traveled,” Mate said. “If it got out of range, that was it. And we could only track one animal at a time.
“Now we receive data on 15–20 blue whales simultaneously, as well as several other species," he added. "The technology is getting better all the time. It isn't unusual now to track whales via satellite for 4–5 months, and we tracked one blue whale for 307 days before the batteries were exhausted. That provides a lot of data.”
Of the hundred whales Mate has tracked, 45 have provided significant long-term data. Those 45 whales traveled a composite 230,000 kilometers and dove some 2.5 million times. “One animal migrated more than 10,000 miles,” he said. The data that comes out of studies like these is significant, Mate says, because it tells scientists and resource managers where whales spend much of their time, where critical feeding and reproductive areas are located, and how much time they spend at the surface - all of which are important in estimating the population size.
“Many of the productive areas for the California blue whales are just 30 miles or so offshore from San Francisco and Santa Barbara, where there is a lot of ship traffic,” Mate said. “But shipping doesn't seem to have much of an effect.”
Last year, Mate tagged a mother blue whale in the Sea of Cortéz and waited for her and her calf to return to California. They never did, staying off the coast of central Baja California. “That goes to show you, there are a lot of mysteries remaining,” Mate said. “It was thought that all of the whales in the Sea of Cortéz were ‘California whales.’ The fact that a mother and her calf stayed down there is interesting; if those movements are typical, it may suggest that we've been underestimating calf production and perhaps the entire population.”
This spring, Mate is planning to tag more blue whales in the Sea of Cortéz. Scientists estimate that there are about 2,100 blue whales off the coast of California each summer, which is about 25 percent of the world’s population and the largest concentration on the planet. These whales will grow as large as 85 feet and 80 tons, while blue whales in the southern hemisphere may reach 100 feet and 120 tons.
An estimated 7,000–8,000 true blue whales are thought to live throughout the world. Mate's research is funded by the Marine Mammal Endowment at Oregon State University and by the Office of Naval Research.
Note to Reporters: Bruce Mate will be out of the office during the week of Feb. 11–15, but he will check his e-mail during that time: (bruce.mate@hmsc.orst.edu). He will return voice mail messages at 541-953-0156.
By Mark Floyd, 541-737-0788
SOURCE: Bruce Mate, 541-867-0236