Peter Tyack: The intriguing sound of marine mammals

32,092 views ・ 2010-06-16

TED


Please double-click on the English subtitles below to play the video.

00:15
Thank you so much. I'm going to try to take you
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on a journey of the underwater acoustic world
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of whales and dolphins.
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Since we are such a visual species,
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it's hard for us to really understand this,
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so I'll use a mixture of figures and sounds
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and hope this can communicate it.
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But let's also think, as a visual species,
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what it's like when we go snorkeling or diving
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and try to look underwater.
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We really can't see very far.
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Our vision, which works so well in air,
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all of a sudden is very restricted and claustrophobic.
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And what marine mammals have evolved
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over the last tens of millions of years
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is ways to depend on sound
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to both explore their world
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and also to stay in touch with one another.
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Dolphins and toothed whales use echolocation.
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They can produce loud clicks
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and listen for echoes from the sea floor in order to orient.
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They can listen for echoes from prey
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in order to decide where food is
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and to decide which one they want to eat.
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01:10
All marine mammals use sound for communication to stay in touch.
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01:12
So the large baleen whales
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will produce long, beautiful songs,
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which are used in reproductive advertisement
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for male and females, both to find one another
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and to select a mate.
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And mother and young and closely bonded animals
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use calls to stay in touch with one another,
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so sound is really critical for their lives.
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The first thing that got me interested in the sounds
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of these underwater animals,
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whose world was so foreign to me,
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was evidence from captive dolphins
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that captive dolphins could imitate human sounds.
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And I mentioned I'll use
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some visual representations of sounds.
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Here's the first example.
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This is a plot of frequency against time --
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sort of like musical notation,
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where the higher notes are up higher and the lower notes are lower,
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and time goes this way.
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This is a picture of a trainer's whistle,
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a whistle a trainer will blow to tell a dolphin
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it's done the right thing and can come get a fish.
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It sounds sort of like "tweeeeeet." Like that.
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This is a calf in captivity
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making an imitation
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of that trainer's whistle.
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02:11
If you hummed this tune to your dog or cat
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and it hummed it back to you,
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you ought to be pretty surprised.
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02:17
Very few nonhuman mammals
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can imitate sounds.
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It's really important for our music and our language.
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So it's a puzzle: The few other mammal groups that do this,
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why do they do it?
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A lot of my career has been devoted
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to trying to understand
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how these animals use their learning,
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use the ability to change what you say
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based on what you hear
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in their own communication systems.
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So let's start with calls of a nonhuman primate.
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Many mammals have to produce contact calls
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when, say, a mother and calf are apart.
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This is an example of a call produced by squirrel monkeys
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when they're isolated from another one.
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And you can see, there's not much
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variability in these calls.
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By contrast, the signature whistle
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which dolphins use to stay in touch,
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each individual here has a radically different call.
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They can use this ability to learn calls
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in order to develop more complicated and more distinctive calls
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to identify individuals.
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How about the setting in which animals need to use this call?
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Well let's look at mothers and calves.
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In normal life for mother and calf dolphin,
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they'll often drift apart or swim apart if Mom is chasing a fish,
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and when they separate
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they have to get back together again.
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What this figure shows is the percentage of the separations
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in which dolphins whistle,
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against the maximum distance.
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So when dolphins are separating by less than 20 meters,
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less than half the time they need to use whistles.
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Most of the time they can just find each other
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just by swimming around.
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But all of the time when they separate by more than 100 meters,
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they need to use these individually distinctive whistles
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to come back together again.
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Most of these distinctive signature whistles
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are quite stereotyped and stable
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through the life of a dolphin.
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But there are some exceptions.
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When a male dolphin leaves Mom,
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it will often join up with another male
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and form an alliance, which may last for decades.
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As these two animals form a social bond,
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their distinctive whistles actually converge
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and become very similar.
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This plot shows two members of a pair.
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As you can see at the top here,
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they share an up-sweep, like "woop, woop, woop."
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They both have that kind of up-sweep.
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Whereas these members of a pair go "wo-ot, wo-ot, wo-ot."
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And what's happened is
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they've used this learning process
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to develop a new sign that identifies this new social group.
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It's a very interesting way that they can
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form a new identifier
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for the new social group that they've had.
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Let's now take a step back
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and see what this message can tell us
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about protecting dolphins
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from human disturbance.
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Anybody looking at this picture
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will know this dolphin is surrounded,
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and clearly his behavior is being disrupted.
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This is a bad situation.
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But it turns out that when just a single boat
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is approaching a group of dolphins
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at a couple hundred meters away,
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the dolphins will start whistling,
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they'll change what they're doing, they'll have a more cohesive group,
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wait for the boat to go by,
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and then they'll get back to normal business.
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Well, in a place like Sarasota, Florida,
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the average interval between times
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that a boat is passing within a hundred meters of a dolphin group
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is six minutes.
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So even in the situation that doesn't look as bad as this,
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it's still affecting the amount of time these animals have
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to do their normal work.
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And if we look at a very pristine environment like western Australia,
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Lars Bider has done work
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comparing dolphin behavior and distribution
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before there were dolphin-watching boats.
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When there was one boat, not much of an impact.
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And two boats: When the second boat was added,
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what happened was that some of the dolphins
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left the area completely.
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Of the ones that stayed, their reproductive rate declined.
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So it could have a negative impact on the whole population.
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When we think of marine-protected areas for animals like dolphins,
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this means that we have to be
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quite conscious about activities that we thought were benign.
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We may need to regulate the intensity
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of recreational boating and actual whale watching
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in order to prevent these kinds of problems.
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I'd also like to point out that sound
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doesn't obey boundaries.
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So you can draw a line to try to protect an area,
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but chemical pollution and noise pollution
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will continue to move through the area.
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And I'd like to switch now from this local,
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familiar, coastal environment
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to a much broader world of the baleen whales and the open ocean.
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This is a kind of map we've all been looking at.
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The world is mostly blue.
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But I'd also like to point out that the oceans
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are much more connected than we think.
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Notice how few barriers there are to movement
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across all of the oceans compared to land.
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To me, the most mind-bending example
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of the interconnectedness of the ocean
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comes from an acoustic experiment
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where oceanographers
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took a ship to the southern Indian Ocean,
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deployed an underwater loudspeaker
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and played back a sound.
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That same sound
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traveled to the west, and could be heard in Bermuda,
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and traveled to the east, and could be heard in Monterey --
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the same sound.
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So we live in a world of satellite communication,
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are used to global communication,
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but it's still amazing to me.
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The ocean has properties
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that allow low-frequency sound
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to basically move globally.
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The acoustic transit time for each of these paths is about three hours.
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It's nearly halfway around the globe.
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In the early '70s,
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Roger Payne and an ocean acoustician
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published a theoretical paper
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pointing out that it was possible
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that sound could transmit over these large areas,
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but very few biologists believed it.
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It actually turns out, though,
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even though we've only known of long-range propagation for a few decades,
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the whales clearly have evolved,
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over tens of millions of years,
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a way to exploit this amazing property of the ocean.
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So blue whales and fin whales
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produce very low-frequency sounds
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that can travel over very long ranges.
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The top plot here shows
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a complicated series of calls
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that are repeated by males.
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They form songs, and they appear to play a role in reproduction,
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sort of like that of song birds.
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Down below here, we see calls made by both males and females
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that also carry over very long ranges.
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The biologists continued to be skeptical
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of the long-range communication issue
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well past the '70s,
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until the end of the Cold War.
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What happened was, during the Cold War,
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the U.S. Navy had a system that was secret at the time,
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that they used to track Russian submarines.
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It had deep underwater microphones, or hydrophones,
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cabled to shore,
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all wired back to a central place that could listen
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to sounds over the whole North Atlantic.
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And after the Berlin Wall fell, the Navy made these systems available
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to whale bio-acousticians
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to see what they could hear.
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This is a plot from Christopher Clark
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who tracked one individual blue whale
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as it passed by Bermuda,
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went down to the latitude of Miami and came back again.
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It was tracked for 43 days,
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swimming 1,700 kilometers,
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or more than 1,000 miles.
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This shows us both that the calls
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are detectable over hundreds of miles
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and that whales routinely swim hundreds of miles.
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They're ocean-based and scale animals
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who are communicating over much longer ranges
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than we had anticipated.
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Unlike fins and blues, which
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disperse into the temperate and tropical oceans,
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the humpbacked whales congregate
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in local traditional breeding grounds,
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so they can make a sound that's a little higher in frequency,
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broader-band and more complicated.
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So you're listening to the complicated song
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produced by humpbacks here.
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Humpbacks, when they develop
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the ability to sing this song,
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they're listening to other whales
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and modifying what they sing based on what they're hearing,
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just like song birds or the dolphin whistles I described.
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This means that humpback song
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is a form of animal culture,
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just like music for humans would be.
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I think one of the most interesting examples of this
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comes from Australia.
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Biologists on the east coast of Australia
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were recording the songs of humpbacks in that area.
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And this orange line here marks the typical songs
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of east coast humpbacks.
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In '95 they all sang the normal song.
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But in '96 they heard a few weird songs,
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and it turned out that these strange songs
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were typical of west coast whales.
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The west coast calls became more and more popular,
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until by 1998,
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none of the whales sang the east coast song; it was completely gone.
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They just sang the cool new west coast song.
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It's as if some new hit style
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had completely wiped out
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the old-fashioned style before,
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and with no golden oldies stations.
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Nobody sang the old ones.
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I'd like to briefly just show what the ocean does to these calls.
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Now you are listening to a recording made by Chris Clark,
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0.2 miles away from a humpback.
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You can hear the full frequency range. It's quite loud.
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You sound very nearby.
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The next recording you're going to hear
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was made of the same humpback song
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50 miles away.
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That's shown down here.
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You only hear the low frequencies.
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You hear the reverberation
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as the sound travels over long-range in the ocean
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and is not quite as loud.
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Now after I play back these humpback calls,
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I'll play blue whale calls, but they have to be sped up
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because they're so low in frequency
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that you wouldn't be able to hear it otherwise.
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Here's a blue whale call at 50 miles,
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which was distant for the humpback.
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It's loud, clear -- you can hear it very clearly.
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Here's the same call recorded from a hydrophone
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500 miles away.
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There's a lot of noise, which is mostly other whales.
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But you can still hear that faint call.
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Let's now switch and think about
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a potential for human impacts.
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The most dominant sound that humans put into the ocean
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comes from shipping.
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This is the sound of a ship,
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and I'm having to talk a little louder to talk over it.
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Imagine that whale listening from 500 miles.
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There's a potential problem that maybe
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this kind of shipping noise would prevent whales
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from being able to hear each other.
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Now this is something that's been known for quite a while.
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This is a figure from a textbook on underwater sound.
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And on the y-axis
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is the loudness of average ambient noise in the deep ocean
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by frequency.
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In the low frequencies, this line indicates
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sound that comes from seismic activity of the earth.
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Up high, these variable lines
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indicate increasing noise in this frequency range
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from higher wind and wave.
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But right in the middle here where there's a sweet spot,
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the noise is dominated by human ships.
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Now think about it. This is an amazing thing:
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That in this frequency range where whales communicate,
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the main source globally, on our planet, for the noise
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comes from human ships,
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thousands of human ships, distant, far away,
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just all aggregating.
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The next slide will show what the impact this may have
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on the range at which whales can communicate.
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So here we have the loudness of a call at the whale.
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And as we get farther away,
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the sound gets fainter and fainter.
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Now in the pre-industrial ocean, as we were mentioning,
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this whale call could be easily detected.
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It's louder than noise
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at a range of a thousand kilometers.
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Let's now take that additional increase in noise
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that we saw comes from shipping.
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All of a sudden, the effective range of communication
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goes from a thousand kilometers to 10 kilometers.
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Now if this signal is used for males and females
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to find each other for mating and they're dispersed,
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imagine the impact this could have
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on the recovery of endangered populations.
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Whales also have contact calls
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like I described for the dolphins.
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I'll play the sound of a contact call used
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by right whales to stay in touch.
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And this is the kind of call that is used by,
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say, right whale mothers and calves
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as they separate to come back again.
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Now imagine -- let's put the ship noise in the picture.
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What's a mother to do
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if the ship comes by and her calf isn't there?
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I'll describe a couple strategies.
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One strategy is if your call's down here,
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and the noise is in this band,
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you could shift the frequency of your call out of the noise band
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and communicate better.
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Susan Parks of Penn State has actually studied this.
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She's looked in the Atlantic. Here's data from the South Atlantic.
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Here's a typical South Atlantic contact call from the '70s.
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Look what happened by 2000 to the average call.
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Same thing in the North Atlantic,
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in the '50s versus 2000.
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Over the last 50 years,
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as we've put more noise into the oceans,
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these whales have had to shift.
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It's as if the whole population had to shift
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from being basses to singing as a tenor.
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It's an amazing shift, induced by humans
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over this large scale,
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in both time and space.
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And we now know that whales can compensate for noise
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by calling louder, like I did when that ship was playing,
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by waiting for silence
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and by shifting their call out of the noise band.
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Now there's probably costs to calling louder
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or shifting the frequency away from where you want to be,
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and there's probably lost opportunities.
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If we also have to wait for silence,
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they may miss a critical opportunity to communicate.
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So we have to be very concerned
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about when the noise in habitats
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degrades the habitat enough
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that the animals either have to pay too much to be able to communicate,
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or are not able to perform critical functions.
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It's a really important problem.
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And I'm happy to say that there are several
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very promising developments in this area,
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looking at the impact of shipping on whales.
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In terms of the shipping noise,
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the International Maritime Organization of the United Nations
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has formed a group whose job is to establish
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guidelines for quieting ships,
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to tell the industry how you could quiet ships.
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And they've already found
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that by being more intelligent about better propeller design,
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you can reduce that noise by 90 percent.
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If you actually insulate and isolate
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the machinery of the ship from the hull,
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you can reduce that noise by 99 percent.
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So at this point, it's primarily an issue of cost and standards.
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If this group can establish standards,
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and if the shipbuilding industry adopts them for building new ships,
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we can now see a gradual decline
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in this potential problem.
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But there's also another problem from ships that I'm illustrating here,
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and that's the problem of collision.
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This is a whale that just squeaked by
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a rapidly moving container ship and avoided collision.
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But collision is a serious problem.
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Endangered whales are killed every year by ship collision,
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and it's very important to try to reduce this.
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I'll discuss two very promising approaches.
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The first case comes from the Bay of Fundy.
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These black lines mark shipping lanes
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in and out of the Bay of Fundy.
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The colorized area
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shows the risk of collision for endangered right whales
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because of the ships moving in this lane.
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It turns out that this lane here
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goes right through a major feeding area of right whales in the summer time,
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and it makes an area of a significant risk of collision.
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Well, biologists
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who couldn't take no for an answer
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went to the International Maritime Organization
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and petitioned them to say,
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"Can't you move that lane? Those are just lines on the ground.
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Can't you move them over to a place
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where there's less of a risk?"
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And the International Maritime Organization responded very strongly,
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"These are the new lanes."
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The shipping lanes have been moved.
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And as you can see, the risk of collision is much lower.
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So it's very promising, actually.
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We can be very creative about thinking
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of different ways to reduce these risks.
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Another action which was just taken independently
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by a shipping company itself
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was initiated because of concerns the shipping company had
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about greenhouse gas emissions with global warming.
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The Maersk Line looked at their competition
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and saw that everybody who is in shipping thinks time is money.
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They rush as fast as they can to get to their port.
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But then they often wait there.
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What Maersk did is they worked ways to slow down.
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They could slow down by about 50 percent.
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This reduced their fuel consumption by about 30 percent,
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which saved them money,
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and at the same time, it had a significant benefit for whales.
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It you slow down, you reduce the amount of noise you make
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and you reduce the risk of collision.
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So to conclude, I'd just like to point out,
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you know, the whales live in
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an amazing acoustic environment.
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They've evolved over tens of millions of years
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to take advantage of this.
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And we need to be very attentive and vigilant
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to thinking about where things that we do
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may unintentionally prevent them
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from being able to achieve their important activities.
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At the same time, we need to be really creative
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in thinking of solutions to be able to help reduce these problems.
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I hope these examples have shown
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some of the different directions we can take
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in addition to protected areas
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to be able to keep the ocean safe for whales to be able to continue to communicate.
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Thank you very much.
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(Applause)
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About this website

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