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.
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.
In
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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