The Gray Whales May Be Starving
An increase in the number of gray whale deaths could be the result of a diminishing food supply, according to an Oregon Sea Grant researcher.
At least 65 whales are reported to have washed up on Mexico's Baja Peninsula, where the animals migrate each winter to bear their young. And that's not all. Additional whale corpses have been discovered along California shores in March and April during the migration of the whales north to their feeding grounds in the Bering Sea.
The apparent higher-than-normal mortality rate has generated widespread speculation. Some researchers point to pollution or changes in seawater caused by a huge salt-evaporation plant in Guerro Negro. Others suspect that the animals were killed by cyanide in fluorescent dye used by drug smugglers to mark the sea during airdrops of illegal narcotics.
But Oregon Sea Grant whale researcher Bruce Mate said the answer might lie in changes to the undersea ecosystem in the whales' summer feeding grounds off Alaska.
Mate, who is based at Oregon State University's Hatfield Marine Science Center, says one possibility for the gray whale mortalities might be that they are not getting enough to eat. The animals spend the summer months in the Bering Sea, between Alaska and Siberia, where they fatten up mostly on bottom-dwelling creatures called amphipods. The whales then fast during their entire migration south without any additional snacking until they reach Alaska again the following summer.
"So, gray whales might go without food anywhere from three to five months," Mate said, "and those that didn't fill up the tank, so to speak, in the Bering Sea may be returning on empty."
Researchers have noted huge changes in the Bering Sea at all levels of the food chain, and some have theorized that those changes are part of an even larger disruption of ocean temperature and biomass patterns.
Mate says those changes might be affecting the amount of food the gray whales can find during the summer -- and they need a lot of food. Not only do they need to fatten up to get through the months when they don't eat, they also need fuel for a 12,000-mile migration from Alaska to the Baja Peninsula -- the longest migration of any marine mammal.
Mate reviewed information on the gray whale fatalities during a recent meeting of the Mexican Society for Marine Mammalogy. Figures indicate that the number of fatalities is the highest recorded in the 24 years that people have kept track of gray whale migrations. The numbers may partly reflect the fact that, this year, people are keeping better track of the whales, said Mate.
Most worthy of attention this year, is the number of adult whales found dead, Mate said. According to his study, more than half of the 65 dead gray whales counted in Mexico were adults and quite a few of the rest were at least one year old. That's a marked contrast to most years when observable gray whale corpses are typically very young a few weeks or a few months old.
"Typically, most of the animals you'd expect to see die during the reproductive season would be newborn calves," Mate said. "Only about 50 percent of calves live to one year of age. But this year, more than half of the dead animals are adults and quite a significant number of the rest are yearlings. This is part of the population we're not used to identifying with such high mortality rates."
Mate also notes that this year's fatalities were spread out over a long stretch of coastline during a four-month period, indicating to him that the deaths were not the result of a localized problem such as pollution or drug-runners' dye.
But he admits it's hard to tell just what is going on, particularly on the hot, isolated shores of Baja.
"Most whales are too far gone by the time they come to shore. It's been virtually impossible to get good diagnostic information on the cause of death for these animals because the area is so remote," Mate said. "By the time a team can identify a mortality and get to it, the warmth of the sun has caused bloating and deterioration in the physiology of the carcass, so good diagnostics really can't be done." Mate said sometimes researchers are still able to collect blubber specimens, "but even that literally melts away in the heat."
Even those whales that wash up in the more temperate shores of California can pose a challenge for researchers because they have often been at sea for several days.
Mate hopes to expand his study next summer if he can muster the required funding. He plans to tag the whales during their northbound migration and to examine their activity in the Bering Sea.
"If [the whales] stay in one spot, it will indicate that they have found significant quantities of food," Mate explains. "Or if they move around a great deal it will suggest that they haven't found what they are looking for either in quantity or quality." Mate also intends to sample the actual food supply.
Anyone interested in adopting a gray whale to aid Mate's study can write to the Hatfield Range Science Center, Newport, Ore. 97365.