Monterey Bay Whale Watch - March 2001 Feature


Gray Whales on Northern Migration
By Nancy Black

Click on small pictures below to see full-size photos (size 33K each).
The northern migration of the Gray Whale has just begun. After spending the winter months off the west coast of Baja California in the protected lagoons where the Gray Whales mate and bear calves, some are now on their way back to their Alaskan feeding grounds.

Click for larger Gray Whale photo The first whales headed north are usually female whales that have become pregnant in recent months. They will arrive in the Arctic Ocean early to start bulking up on amphipods, their primary prey, in order to support their calves that will be born next winter in the lagoons. Numbers of migrating Gray Whales will be increasing through March and early April as the remainder of males, females, and juveniles head north. After the majority of adults and juveniles pass, the mothers with their calves will travel north along the Monterey coastline through April and May.

This has been an unusual migration year for the Gray Whales. As of March 3, we are seeing whales going both south and north, with numbers of northbound whales increasing each day. Normally all the southbound whales would have passed by mid February. No one has an exact explanation for this occurrence, but guesses are that warmer fall temperatures delayed ice formation, allowing the whales to feed longer in Alaska. Each year as the ice begins to cover some of the whales' feeding areas in the Arctic Ocean they start their trek south. Since the whales normally fast during the migration and in the Mexican lagoons, a thick blubber layer is needed in order to survive long months without food.

The conditions in the Bering Sea have been changing, and in the last few years the combination of less food with increased numbers of Gray Whales may require some whales to spend more time feeding. If pregnant females don't bulk up on amphipods they may not be able to support their calves through lactation. This phenomenon has occurred the last 2 years, supported by the low numbers of mother/calf pairs counted by the National Marine Fisheries Service on the northern migration. We don't yet know what will occur this season with the calves.

Population estimates through the National Marine Fisheries Service indicate there are over 26,000 Gray Whales migrating from Alaska to Mexico and back again each year. The number of whales is high and the Gray Whale is the only whale, once endangered, to recover and has been delisted as an endangered species. Numbers of whales may have reached carrying capacity for the feeding grounds and may level off. Gray Whales are also expanding their feeding range and some whales feed south of Alaska down as far as northern California.

Killer Whales are the only natural predator of the Gray Whale, and our research this spring will focus on the predation behavior of Killer Whales on Gray Whale calves that migrate north with their mothers. Killer Whales tend to target the calves, especially when they cross the Monterey Submarine Canyon. We will continue our research with the National Geographic Society to document this incredible natural event.

Click for larger Gray Whale photoIn summary, the Gray Whales will be increasing in numbers as peak numbers migrate north past Monterey during March and early April. During April, we expect to see the first Humpback Whales arrive in Monterey Bay to feed during the summer and fall. The Humpback Whales are still endangered but are on the increase as their population off California has doubled over the last 10 years.


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Photos by Nancy Black.

Last updated March 4, 2001