6 March 1999
On Board the Department of Conservation Vessel TOHORA
South Bay, Kaikoura, New Zealand

Listening to the Whales - Part Two

As we neared our destination, we were presented with a sight that I have to admit made my heart race a good deal faster than normal. There, about 300 meters ahead of us, was a large, solitary sperm whale swimming slowly along at the surface, exhaling huge blasts of spray. We watched him for nearly ten minutes when both Keith and Bernard, both of whom have seen many more whales that I have, said that the whale was ready to dive. Sure enough, after the next blow the whale arched his back, raised his flukes high above the surface and dove head first into the depths of Kaikoura Canyon where for the next forty five minutes he would search the darkness for food - including the giant squid.

Since this was obviously a good place to listen to the whales as they dove, Bernard decided that we should set out the hydrophone array and start recording. The actual details of how this is done and how the data are interpreted and will be used in our search for the giant squid will be described by Bernard in another journal.

Once we selected our site, Keith shut off the engine and Bernard started to open the large plastic storage boxes that held all of the line, floats, hydrophones, computers and all sorts of other bits and pieces that we were going to use. The first thing that Bernard did was to set the digital wristwatch that was strapped to the line just above the lowest hydrophone, which by the way looks like a large, amber colored gumdrop. Bernard told me that after considering all sorts of complicated and expensive means to calibrate the timing of the hydrophone array, they decided that a cheap digital wristwatch with an alarm was the best solution. Bernard carefully lowered the hydrophone over the side and slowly lowered it down to 40 meters depth. When that depth was reached, Bernard clipped a small white buoy to the line and continued to let more line out until it streamed about 100 meters downstream of our boat.

Bernard checked that the first hydrophone was working (which it was) and then we turned our attention to deploying the second hydrophone array. This one was supported by a much heavier line than the first and had four hydrophones on it (10, 20, 40 and 80 meters depth) as opposed to just one on the first array. And then, as if this wasn't enough to handle, Bernard attached a very heavy weight which in its prior life was a railway hammer to an extra 40 meters of line which he then tied to the very bottom. Because of the strong currents in the Canyon, Bernard found that he needed to add this extra line and weight t make sure that the hydrophones were as close to vertical as possible.

For this deployment, Bernard used only two hydrophone lines. At other times, a third hydrophone is hung from the bow of the boat at a depth of 40 meters. With the hydrophones in the water, Bernard took out his notebook and recorded a few key facts about the day, our location (which we continuously monitor using a small, hand held Global Positioning System unit) and the location of the whale we were listening to. The resident whales in Kaikoura have all been given names by the Whale Watch Kaikoura folks. In this particular case, the whale that we were listening to was named "Droopy Flukes". In talking with Bernard, I learned that the whales stay at the surface for precisely 10 minutes and then dive. And then at exactly 20 seconds into the dive, not 15 and not 25, the whales start emitting the sonar pings that we were here to record. Rather than record them on a traditional tape recorder, Bernard uses a computer that records each of the hydrophone's signals (5 in this case, or 6 when the third hydrophone array is used) at a data rate of 10 megabytes per minute. With a typical dive lasting 45 minutes, the data volume becomes quite significant. After a few hours of recording, you can begin to imagine the volume of data that has to be analyzed.

Bernard connected a small speaker to the computer so that we could actually listen to the sound of the whales. After several hours of listening to the whales of Kaikoura Canyon, the best description that I can give of what it sounded like (136 kb .wav) was to imagine a portable radio filled with background static through which you are listening to the sound of a steam-driven pile driver hammering things once per second. Although the patterns of the sounds would change periodically (as will be described in a later journal by Bernard), the regular pattern over such a long period of time really amazed me.

Continues...next journal

 


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