As winter approaches, we look forward to the annual migration of the Gray
Whale. These whales are now a success story, having recovered from near
extinction. They are the first marine mammal ever to be removed from the
endangered species list.
As of early December, most of the Gray Whales have left their summer
feeding grounds and are now making their way down the west coast to their
breeding and calving areas off Baja California. Off Monterey, we have
already spotted a few early migrators. Their numbers will increase through
December and January on the southbound migration. Then during mid-February, with some whales still headed south, the first northbounders will be passing by. Their numbers will increase through March. Since
the population of Gray Whales is now more than 26,000, we expect to see Grays
passing our coast each day from mid-December through April and into May.
Although the Gray Whale has recovered, they are still being monitored.
For many years the National Marine Mammal Lab (part of NOAA) has monitored
the Gray Whales by operating a count station just a few miles south of
Monterey. The whales migrate within a few miles of shore near Monterey so
they can easily be counted, and then an accurate population estimate can be
derived. In addition, another crew from the National Marine Fisheries Service
counts the number of mother/calf pairs as they migrate north in spring. This
is an excellent indicator of how the population is fairing.
Some interesting findings have occurred over last few years. Last year
was the lowest mother/calf pair count since the surveys were begun over five
years ago. Wayne Perryman, a scientist with NMFS, has attributed the low
number of calves over the last two years to poor feeding seasons for the Gray
Whales during summer in the Bering Sea. Longer periods of ice covering the
whales' feeding areas, due to colder ocean temperatures associated with La
Nina (the cold water period after an El Nino), have prevented females from
feeding throughout the season and building up enough reserves to successfully support
their calves, resulting in a lower reproductive rate. Other things may be a
factor, such as an overall decline in the productivity of the Bering Sea,
which could affect the amphipods the Gray Whales feed on.
Normally these little animals that bury in the mud are extremely abundant,
but the changing ecology of the Bering Sea with lower production may result
in less food for the whales.
In addition, the population may have reached carrying capacity, and there
may not be enough feeding areas to support such a large number of whales,
which would naturally result in lowering the population. There is some indication that this is taking place; over the last two years, a number of Gray Whales
have washed up along the beaches on the northern migration, possibly a result
of not feeding well enough the previous summer. The Gray Whales feed during
the summer and for the most part spend the migration period and wintering
period fasting while living off the blubber layer they gained from summer.
Something we are following closely is the predator/prey relationship
between the increasing Gray Whale population and their predator, the Killer
Whale. We have been studying the Killer Whales in Monterey Bay for close to
15 years, and now focus our research most intensively during the spring when
the Gray Whales migrate north with their calves. At this time, Killer Whales
are often hunting for them in Monterey Bay. We will continue to work with the
National Geographic Society for a third year on this research, which will also
result in a feature film. We have found a correlation between the number of calves for a season and the number of Killer Whale attacks on Gray Whales. Last year, the lowest calf year, we saw no
predation events. This predator/prey relation is an amazing event of nature
that has been occurring for thousands of years. Just over the last ten years,
we've begun to learn more about how the Killer Whales work as a coordinated
group to overcome these larger whales and teach the Killer Whale calves to hunt.
During 1997, the BBC Natural History Unit in England accompanied us
during our research and for the first time filmed this incredible event. This will be part of a television series entitled the Blue Planet (similar to Trials of Life), scheduled for broadcast in the U.K. in January 2001 and in the U.S. in fall 2001.
Our Gray Whale trips will begin December 15 and continue daily until April 30 (except for Christmas and Easter). Although
we can celebrate the recovery of the Gray Whale, as we are rewarded while
watching the many pods migrate past our coast, we must continue to protect
their habitats and monitor their population in years to come. We hope our
endangered population of Humpback and Blue Whales, which feed in Monterey Bay
during the summer and fall, will enjoy a similar recovery.
|
|