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Humpback Whales use a number of feeding strategies to harvest the
rich waters of South East Alaska, but by far the most impressive is the
cooperative feeding behaviour for herrings, known as bubble netting. It
is remarkable in terms both of the sheer spectacle and of its
indication of the intelligence and skill that enables the whales to
fish for herrings using bubbles, the sea’s surface and incredible
sound.
To find the whales can take hours, even days, of
patient searching. The blow is typically what you first see. In the
right light you can spot the plumes of breath from miles out and
quickly get an idea of the size of the group. On still mornings the
sound of the blow can carry far across the water. It’s usually the
characteristic noise of a strong exhalation, but occasionally
individuals stand out, some with rasping breaths, others sounding like
foghorns.
Recording whales is all about patience, prediction,
and good boat etiquette. Predicting where they’ll come up is partly
luck, partly judgement. The direction that the pod is moving can be
worked out by the following the direction of the last fluke down, but
guessing how long they’ll stay down is where the luck comes in. As
you’re tracking at a distance, it’s vital to keep the boat’s speed low
and constant. Revving engines or constantly changing speeds creates
sonic mayhem underwater, so a calm, careful approach is the only
method.
The whales dive as a team. One by one, backs arch and they slip beneath the surface. Tails out of the water indicate that they’ve dived for a while, so we let the boat gently move forward and then cut the engine to listen. It’s the suspense of waiting for the whales that makes watching bubble netting so exciting. From beneath the water comes the muffled moan of a single humpback – the net is being laid. The underwater sound is so loud you can hear it when you are standing on the boat. The moan gets louder and louder, and all eyes are now scanning the sea, looking for the first bubbles to break the surface.....
Next week you can hear the stunning sounds captured by the hydrophones and read the second half of Joe Stevens' diary of bubble netting Humpback Whales.
Next report:
Joe Stevens' audio of Humpback Whales bubble netting
Last 2 reports on Humpbacks:
How Humpbacks migrate
Tagging satellite transmitters to Humpbacks