Humpback Whales, Dolphins, Sea Lions, and Sea Birds in Multi-Species Feeding Aggregations in Monterey Bay
By Nancy Black
Since early May we have observed an incredible feeding phenomenon. Groups of
5 to 10 Humpback Whales have been feeding with hundreds of Long Beaked Common
Dolphins and on some days with Pacific White-Sided Dolphins, along with up to
100 California Sea Lions, and thousands of Sooty Shearwaters. This activity has
occurred on a regular basis over the last few weeks and may continue into the
summer. The reason for this concentrated multi-species feeding activity seems
to be the tremendous number of sardines and anchovies in Monterey
Bay. In addition to these aggregations there are many other Humpbacks in the
Bay feeding individually or in small groups.
Every year we see feeding Humpback Whales and dolphins on a regular basis,
but this year has been extraordinary. The dolphins appear to herd the fish up
toward the surface and the whales often lunge feed through the balled up
fish. In this way, the whales are benefiting from the dolphins' ability to herd
fish. At times, we have seen as many as three Humpback Whales simultaneously
lunging out of the water with their mouths wide open and throat pleats
extended. Such cooperative feeding events by whales are usually rare here, but
Humpback Whales are known to feed by a variety of methods and this behavior is
probably the result of huge fish concentrations. In Alaska during cooperative
feeding lunges, the whales usually produce sounds that coordinate the
individual whales to lunge simultaneously. Our local biologists will be using a
hydrophone (underwater microphone) in an attempt to record such sounds. We
also have been photo-identifying individual whales by the underside of their
tail flukes to document how many different whales are involved in this
activity.
In addition to the whales and dolphins, the sea lions are right in the middle
of this feeding frenzy and usually dive together in small groups to feed on
the fish. We have been able to locate this activity due to the
large number of shearwaters flocking over the feeding area.
These seabirds also benefit by diving down to catch the surface fish
as the dolphins drive the fish toward the surface. We have estimated up to
10,000 shearwaters in
some of these flocks. By using binoculars we can locate these flocks from
several miles away. Most of this action has been happening near the edge of
the Monterey Submarine Canyon, an area that seems to concentrate prey.
Although the feeding activity shifts to different areas, it has been happening
within the inner Bay on a fairly regular basis.
The other amazing feature about these multi-species feeding aggregations is
that they are very concentrated with all the animals tightly bunched together in
one area. The amount of fish available for 10 whales, 500+ dolphins, 100+ sea
lions and 5,000+ seabirds must be enormous. The warmer water conditions
related to El Nino could be a factor as sardines are associated with higher
water temperatures. Sea temperatures in the Bay are still 2-4 degrees above
normal. Most passengers who have witnessed this activity have never seen
anything like it, something that is comparable to large aggregations of
animals in Africa.